2016 Vol. 45, No. 1
2016, 45(1): 101001.
doi: 10.3788/IRLA201645.0101001
Astronomical telescope is always one of the vital tools that help human kind to unveil hidden natural laws in the universe. However, spatial resolution of the large ground-based telescope was severely limited because the turbulence of atmosphere degenerates the perfect wavefront from stars into an aberrated one, which was the key science and technology difficult problem to achieve high resolution astronomical observation. So adaptive optics(AO) was being pursuit by many teams internationally to correct the wavefront aberration and make large ground-based telescope resolving power to near diffraction limitation. It indicates that the ground-based optical telescope was currently turning into the AO telescope age. Sodium laser guide star(LGS) generated by laser exciting sodium atoms in the mesospheric layer at an altitude of about 90 km, as a beacon of AO correction, was the cutting-edge technology for the AO telescope. The theory, methods and development status of the sodium LGS were described in this paper. Especially in our lab, micro-second sodium LGS laser system suitable for efficient excitation of the sodium layer was developed with spectral format matched to the mesospheric D2 line. The sodium LGS laser system was successful to apply in some domestic and overseas large telescopes.
2016, 45(1): 102001.
doi: 10.3788/IRLA201645.0102001
Through testing the detection process of infrared(IR) up-conversion step by step along with theoretical calculation, the IR response characteristics of the cascade IR up-converter(CIUP) and the whole up-conversion system were thoroughly studied. Test results show that CIUPs can achieve considerable IR responsivity under weak background luminescence. The responsivity of the CIUP rises very fast under the flat-band bias and the conversion process from IR light signal into CIUP's electrical signal displays excellent linearity. By applying the ABC model to the near-infrared radiation process of the CIUP, the fitted response current of the up-conversion system and the fitted current conversion efficiency agree well with the measured data, which gives a reasonable explanation for the non-linearity of the system's IR response.
2016, 45(1): 102002.
doi: 10.3788/IRLA201645.0102002
For laser measurement to space debris adopting large aperture telescope will help to increase the ability of detecting laser echoes. According to laser link equation adopting multi-relative-small aperture telescopes could achieve the ability of receiving the laser echoes from one large aperture telescopes and the disadvantages for the large telescope, such as fast tracking ability, system running maintance and so on could be offest and with the measuring ability and efficiency. Based on the 1.56 m aperture of astronomical telescope about 55 m far from the 60 cm telescope at Shanghai Astronomical Observatory Chinese Academy of Sciences, the method of laser measurement with two receiving telescopes have been investigated and the observing experiments of space debris for the first time in China are also performed to validate the feasibility of synchronously receiving laser echoes by multi-receiving telescopes. It is indicated from the measuring results that the receiving ability for 1.56 m telescope is approximate three or four times higher than that of 60 cm telescope and the equivalent receiving aperture of 1.65 m telescope can be derived, which will play an important role in high precision laser ranging to far-distance and small-size space debris in future.
2016, 45(1): 106001.
doi: 10.3788/IRLA201645.0106001
A new lidar low-level wind shear alerting algorithm based on ramps detection was presented in this paper. Glide path scanning and combination of double and simple ramp detection had been applied in this new algorithm. Firstly, the lidar radial velocity was projected onto the glide-path and headwind wind profile was restricted into. Secondly, single ramps and the changes of double ramps declivity were detected by the new algorithm. The results on provisions of international low-level wind shear threshold and the wind shear alerting discriminating judgment formula was compared to come to the conclusion. The performance of the proposed method was verified through the real data from Hong Kong Observatory. The results show that the proposed algorithm detects the wind shear which the single ramp fails to detect. The new proposed method is effective, it is significant to raise the alarm rate.
2016, 45(1): 106002.
doi: 10.3788/IRLA201645.0106002
The atmospheric scattering effect is important influence factor on received pulse waveform of satellite laser altimeter. According to the relationship expression between the received pulse signal (RPS) and atmospheric response function, the geometric track and scattering probability of laser beam were analyzed under the condition of ignoring multiple atmospheric scattering effects. Moreover, the analytic models on characteristic parameters of scattering laser pulse and RPS were deduced. In terms of geosicence laser altimeter system(GLAS) parameters, the impact of atmospheric medium distribution, laser pointing angle and slope angle on characteristic parameters of RPS were simulated by using method of numerical simulation. The results show that the maximums of energy, centroid and RMS pulse-width of RPS are separately more than 15%, 250 cm and 800 cm, when the ranges on height and particle radium of scattering medium are 0.2-6 km and 0-120 m. Meanwhile, with the increment of laser pointing angle and target slope angle, the energy of RPS remains basically unchanged, but the centroid and RMS pulse-width present incremental trend. The Gaussian fitting algorithm contributes to reduce the influence of atmospheric scattering effect on RPS. The final conclusion has instructive significance for the processing and analysis of RPS and assessment of laser range precession.
2016, 45(1): 106003.
doi: 10.3788/IRLA201645.0106003
Range gate is an usual anti-jamming technology for laser guidance. Extraction probability of laser jamming signal in range gate is very important to successful jamming. According to the connection and independence between jamming signal and guidance signal in range gate, it was put forward that the joint probability density function was compatible with laser signal extraction in range gate under jamming. The effect of jamming signal in range gate pull off was thought about. The quantitative relation between extraction probability of jamming signal and advance-synchronizing time was simulated in different width range gate by calculational software Matlab. The results show that there is an optimal advance-synchronizing time for a real-time range gate of which width is fixed. Extraction probability of jamming signal is 0.5, not 1.0, when advance-synchronizing time is zero. The jamming signal is easy to be extracted by range gate when the timing of jamming devices is good or the range gate is wide. Jamming signal extraction probability increases and the width of range gate is insignificant after the range gate is pulled off. The results of laser signal extraction in range gate during once guidance process and tracking target or false target during repetitious guidance process were simulated by Monte-Carlo. It is beneficial to the construction of assessment system of effectiveness about angle deception jamming.
2016, 45(1): 106004.
doi: 10.3788/IRLA201645.0106004
Optical rectification effect is one of the effective ways to generate terahertz(THz) wave, and the generation of high-power THz wave requires femtosecond laser with high intensity to excite optical rectification crystals. However, the crystal will be damaged if the intensity of femtosecond laser is too high, seriously affecting the output of high-power THz wave. Therefore, it is of great importance to study the damage thresholds of optical rectification crystals for both theoretically and practically. In this paper, the interaction mechanism between the femtosecond laser and the nonlinear optical rectification crystals was analyzed, and the prediction model of damage thresholds of optical rectification crystals under femtosecond laser was built up. Then on this basis, the variation of damage thresholds of LiNbO3,ZnTe and ZnSe crystals with the pulse duration of femtosecond laser was compared and analyzed. The results show that, the photoionization dominates in the whole process when the pulse duration of femtosecond laser is relatively short, while the avalanche ionization gradually plays an important role with the increase of pulse duration. Avalanche ionization rate and photoionization rate are related closely with the forbidden band width of the crystal. Consequently, the greater the forbidden band widths of optical rectification crystals, the higher the damage thresholds are. The damage thresholds of LiNbO3 are higher than those of ZnTe and ZnSe crystals, which is more suitable for the generation of high-power THz wave.
Raman detection is often disturbed by fluorescence background, while Shifted Excitation Raman Difference Spectroscopy(SERDS)is an effective method for fluorescent suppression on Raman spectroscopy. Based on this method, a Raman spectroscopy measurement system was designed using two closely space fixed-wavelength laser diodes stabilized with the Volume Bragg Gratings. The output wavelength of laser diodes was stabilized by manipulating their power and temperature. The light path and circuit of spectral data acquisition were designed with back-thinned area array CCD with high sensitivity. Besides, the three different reconstruction algorithms of the difference spectrum, namely simple integration algorithm, simple integration with data interpolation algorithm and multiple energy constraint iterative deconvolution algorithm could be realized through software of this system. The Raman spectra of sesame oil of some brand in the presence of a highly fluorescent were measured with this system and then the spectra reconstructed with three different algorithms to process the difference spectrum respectively were compared. Experimental results show that the system designed in this paper can effectively reject the effect of fluorescence to the Raman spectroscopy measurement.
2016, 45(1): 106006.
doi: 10.3788/IRLA201645.0106006
In order to understand the influence of picosecond laser irradiation on crystalline silicon, laser-induced changes of crystalline silicon by picosecond laser ablation with different average laser powers were studied. Then X-ray photoelectron spectroscopy and transmission electron microscope were used to analyze the influence of average laser power variation on final chemical composition and microstructure of the ablated silicon, respectively. It is concluded that, with the increase of average laser power, the relative content of Si in ablation product keeps falling, by contrast, the relative content of SiO2 gradually rises. At the same time, the increase of average laser power intensifies the amorphization degree of microstructure of ablated silicon. Finally, it is deduced that the increased laser fluence resulted from average laser power increasing is the main reason for all of above experimental results, and also to enlarge and deepen the thermal and mechanical damages in ablated silicon.
2016, 45(1): 106007.
doi: 10.3788/IRLA201645.0106007
For the characteristics of wavelength and output power,discharge initiated repetitively pulsed HF laser has become the hotspot in mid-infrared laser device technology research field. In this paper, numerical simulation of flow field in discharge region and structure design of inject pipeline with repetitively pulsed HF laser device was described. Under the investigation of discharge characteristics in SF6/C2H6 gas mixture and output characteristics of laser pulse, the flow field uniformity and repetitively pulsed laser energy stability were researched. It is shown that with the optimized design of inject pipeline, the flow field uniformity improved obviously. The minimum flow velocity for gas circulation is elevated to 6.5 m/s. The deposited energy per unit volume gas with stable volum discharge increased from 1.6 J/mlatm to 2.0 J/mlatm. The maximal running frequency of 100 Hz and the average power of 40 W are obtained. The system operating stability keeps well.
2016, 45(1): 105001.
doi: 10.3788/IRLA201645.0105001
248 nm KrF excimer lasers have important applications in many areas such as photoetching and scientific research. The excimer laser for writing Fiber Bragg Grating was developed. The mechanical structure was designed and improved, and the key technologies including uniform discharge and preionization were analyzed. The laser performance was optimized by studying the impact of the charging voltage, the gas mixture and the total gas pressure on output energy and efficiency. The beam profile homogeneity, beam divergence angle and energy stability were measured and calculated. The repetition rate of the excimer laser is 1-50 Hz, and the maximal output efficiency is about 2.0%, and the maximal single pulse output energy is up to 360 mJ. The instability of output energy is less than 1.8% with charge voltage above 24 kV. Writing Bragg Grating in optical fiber core with a static phase-mask by the above laser as light source, of which results were analyzed and discussed.
2016, 45(1): 105002.
doi: 10.3788/IRLA201645.0105002
An efficient acousto-optic Q-switched Nd:YVO4 self-Raman laser in-band pumped at 880 nm was demonstrated. Using two 10-mm-long Nd:YVO4 crystals as gain medium, 6.11 W of average output power at 1 176 nm Stokes wavelength was obtained under the incident pump power of 26.8 W and a high pulse repetition rate of 190 kHz, corresponding optical efficiency was 22.8%. The influence of Raman-gain-length on conversion efficiency was investigated in the experiment and the dips on Stokes output power was also discussed. Control experiment of the self-Raman laser under 808 nm traditional pumping shows that in-band pumping help improve the conversion efficiency and maximum output power greatly.
2016, 45(1): 105003.
doi: 10.3788/IRLA201645.0105003
In this paper a research about adjustable narrow-width pulsed laser diode driver was introduced which is based on the Lateral Double-diffused MOS(LDMOS). Through the analysis of the semiconductor laser driving circuit theory, circuit-level model of RF power transistor was established by using PSPICE simulation software to gain more optimized drive circuit with theoretical calculations. High-speed current-feedback operational amplifier effectively improved the slew rate and the narrow pulse signal frequency response characteristic. The experimental results show that the laser diode driver can generate 2 A current and the pulse width is adjustable from 20 ns to CW, the rise time and fall time are below 10 ns, the pulse repetition frequency is adjustable from 0 to 10 MHz, which demonstrates the feasibility of the design idea to further improve the output performance of semiconductor laser.
2016, 45(1): 105004.
doi: 10.3788/IRLA201645.0105004
High-power asymmetric pump combiner is the key passive optical device of the high-power continuous all-fiber laser. Multiple pump lights are efficiently coupled into the main fiber through the high-power asymmetric pump combiner, so that enough pump powers are provided for the high-power fiber laser. The current coupling theory of the double waveguide directional combiner can't be directly applied to the study of the high-power asymmetric pump combiner. In order to solve this problem, the incomplete coupling theory of the double waveguide directional combiner was used as the foundation and the asymmetry was used as the feature of the high-power pump combiner. The coupling coefficients equations and the power equations of the high-power asymmetric pump combiner were further derived and the simulation results were also obtained. The conclusions are as follows. The powers of the pump fiber and the main fiber change periodically. When the taper angle of the pump fiber is between 1 and 1.5, more than 97% coupling efficiency is obtained. The local variation of the coupling length has little effect on the coupling efficiency. The conclusions are instructive for the designs and productions of high-power fiber coupler.
In order to expand the low reflective properties of silicon solar cells in a perfect frequency range, a kind of optical microstructures composed of period arranged spherical silica particle was designed. The excellent anti-reflective property of optical micro/nano-structure was used to expand the ultra-low reflective property of silicon solar cells. First, the scattering property of a single spherical silica particle was studied using Mie scattering theory. Then, the reflective property of periodic two-dimensional optical micro-structures composed of multiple particles was analyzed by simulation software MEEP. The results of the simulation demonstrate that when the radius, spacing and periodic number of spherical particles are reasonably selected, the ultra-low reflection will occur in a perfect frequency range.
2016, 45(1): 123001.
doi: 10.3788/IRLA201645.0123001
Frame transfer CCDs play a very important role in hyperspectral remote sensing, while smear has become one of the greatest obstacles for frame transfer CCDs used in hyperspectral imaging and other applications with high frame rate. In order to reduce the smear effect, a clock propagation model consisting of the driver, transmission line and the internal structure of the CCD were established, which better predict the clock waveforms inside and outside of the CCD. The effect on the clock waveforms with typical values of the parameters was simulated, and the simulation and measured results shown great consistency. The driving electronics was optimized based on the simulation, resulting in a line transfer time of as short as 100 ns, which is equal to a smear factor of within 1% under a frame rate of 500 fps, showing the ability of frame transfer CCDs to operate at higher frame rates.
2016, 45(1): 118001.
doi: 10.3788/IRLA201645.0118001
The method based on energy deposition to analyze the influence of -ray radiation on fiber refractive index was proposed. The fiber dispersion variable which changes with the fiber V parameters and refractive index was analyzed and calculated. The radiation effects on fiber dispersion measurement experiments were accomplished, which demonstrates that the radiation impact on the presence of fiber dispersion. The fiber dispersion coefficient variation data with radiation dose were obtained. Experimental and theoretical results show that:(1) fiber dispersion coefficient increases with radiation dose, within the dose range of(0-500 Gy) fiber dispersion coefficient showed a gradual increase in the amount of saturated trends; (2) changes in the refractive index of the fiber lead to the additional material dispersion. The electron density increases caused by radiation is the major factor that results in changes in the refractive index; (3) the decrease of ultra-fast pulsed signal amplitude caused by radiation-induced loss is more significant than pulse broadening caused by radiation-induced dispersion. Both effects exist simultaneously. The pulsed signal distortion is the result of two joint action of especially for long distance optical fiber with nuclear radiation exposure.
2016, 45(1): 118002.
doi: 10.3788/IRLA201645.0118002
One set of infrared optical system which was based on a 360 continuous-scan focal plane array was realized. This optical system contained one afocal telescope, one compensation scan-mirror, and one re-imaging object lens. A cooled focal plane array sensor was utilized. The scan-mirror was used for azimuth compensation. It scaned at a special angular velocity according to the double angle relationship in the opposite direction, thus the system could solve the problem of image smear. Image space scanning was adopted by the system, thus the size of the scan-mirror can be reduced from about 40 mm210 mm under object space scanning to 14 mm22 mm now, and the weight of the scan-mirror could be reduced by more than 95%. Now the swing frequency could reach 100 Hz, which enabled the system to finish 360 azimuth-scan in one second. This system was succinct and compact. It contained eight pieces of lens and one piece of reflective mirror. The image quality was close to the diffractive limit. The laboratory test result shows that, when the scan-mirror is fixed, the image of the small circle hole is blurred, and has smear ghost phenomenon. After the scan-mirror compensation, the image of the circle hole is clear and without smear or distortion, and the image quality is similar to that of the starring system.
2016, 45(1): 118003.
doi: 10.3788/IRLA201645.0118003
To satisfy the requirements of space ultraviolet autonomous navigation sensor, a method based on usual glass combination was proposed to supersede costliness special glass such as CaF2. An ultraviolet star sensor was designed, whose waveband was 330-365 nm, F number was 1.6 and field of view was 88. The ghost suppression target was calculated by paraxial ray tracing. The paraxial first-order ghost was preliminarily analyzed and estimated by Code V, then the off axis multi-orders ghost and energy distribution was simulated by non-sequential ray tracing technology. The results show that this optical system has compact structures and high image quality. The dispersion spot radius is smaller than 10 m, and relative distortion is less than 0.05%. With a target dynamic range of 7 magnitudes, the ghost irradiance of the brightest star is 1/21 of the darkest star and meets the requirements of ultraviolet star sensor.
2016, 45(1): 118004.
doi: 10.3788/IRLA201645.0118004
In order to satisfy the demand for the big aperture diffraction space telescope, a primary lenses deployable structure for space membrane diffractive telescope was investigated. Firstly, after analysis of the characteristics of diffraction imaging about the big aperture membrane diffraction telescope, the main requirements for deployable structure were put forward. Then according to these design requirements for the deployable structure, a 3D solid model was designed. Finally, with the help of Adams, a simulation model was established and analyzed. The results show that the structure under the driving of the rotating drive components is in line with the design form of exercise and achieved smooth and reliable movement. This deployable structure may provide a new train of thought for the design of large aperture membrane diffraction telescope.
2016, 45(1): 118005.
doi: 10.3788/IRLA201645.0118005
Laser beam far-field superposition is an effective method for improving the far-field target surface energy. Changes of the parameters for unit beam will influence the far-field combined beam. In order to analyze the impact of pulsed laser parameter's control on the far-field energy distribution, the Fraunhofer diffraction integral formula was used and the analytic formula of far field intensity for four beams of ordinary pulsed Gauss beam synthesis was deduced and the specific relationship about laser center wavelength and pulse width change with the far-field stack power were proposed. Through the numerical simulation of MATLAB, the results show, when the center wavelength of beam decreases or pulse width decreases, the far field energy converges to the center axis and the far-field on axis intensity will increase. When the on axis intensity relative to the ideal center wavelength and pulse width in the far field intensity on axis changes rate is less than 5%, the center wavelength maximum rate of change should not exceed 7.89%, or pulse width maximum rate of change should not exceed 91%. Therefore, the center wavelength will have a greater impact on far-field intensity distribution compared with pulse width.
2016, 45(1): 118006.
doi: 10.3788/IRLA201645.0118006
Profit from the rapid development of embedded software and hardware, wearable imaging device has become a new trend and exerted a profound influence on traditional portable imaging equipments. Choosing Jorjin AP Module as the core, which integrates Texas Instruments Heterogeneous dual-core processor Synchronous Dynamic random access memory, SDRAM, NAND Flash and Power Management IC, utilizing low power consumption small size low-light camera and high resolution Organic Light Emitting Diode micro-display display, an embedded platform was designed to be applied to auxiliary target observation in low-light conditions. Platform creatively transformed video signal from parallel format into differential format, which not only improved the stability and transmission distance, but also reduced the number of physical interface's lines and made it more flexible to support more kinds of application scenarios. With the advantage of strong algorithm processing ability, low power consumption, light weight, wireless communication, video storage and battery powered, platform can be deeply used in improving users' target detection ability at night in industry, science, military and other fields.
2016, 45(1): 118007.
doi: 10.3788/IRLA201645.0118007
In order to reduce the surface scattering loss of optical thin film, the expression of interface roughness scattering field in the incident medium was given by electromagnetic field boundary conditions, without considering the effect of multiple scattering. The conditions of zero scattering and anti-scattering of single layer optical thin film were discussed. The theoretical results show that when the optical thickness of the film is an even time of /4, the refractive ratio of the single layer thin film must be bigger than the substrate refractive ratio so as to realize anti-scattering, and the air-film micro-roughness must be smaller than the film-substrate interface micro-roughness, when the optical thickness of the thin film is /4 an odd number of times, single layer optical thin film to realize anti-scattering must be single-layer thin film refractive index is less than the substrate refractive index, and the air-film micro-roughness must be satisfy certain conditions.
2016, 45(1): 118008.
doi: 10.3788/IRLA201645.0118008
Operating microscope is a necessary tool in microscope surgical operation, and the object lens is one important part of the operating microscope. The working distance and magnification in the operation should be adjusted to meet the needs of different users, thus a continuous zoom object lens was designed. The continuous zoom object lens is consisted of a set of double agglutinate positive lenses and negative lenses, which is zoomed by mechanical compensatation and moves axially. The operating area of the continuous zoom object lens is from 20 mm to 125 mm, the working distance is from 150 mm to 350 mm, and the focus is from 230 mm to 400 mm. The interval between the positive and negative lenses and the curve of zoom position was also put forward.
2016, 45(1): 104001.
doi: 10.3788/IRLA201645.0104001
A front-end circuit for uncooled diode infrared detector, composed of Gm-C-OP integrated amplifier, was designed. The small input voltage steered from diode detector was transferred into current by an operational transconductance amplifier(OTA), and then the current was converted to voltage by a capacitor transimpedance amplifier(CTIA). The OTA used a current feedback loop to achieve higher linearity and transconductance than the traditional one. By adopting differential input structure, Gm-C-OP integrated amplifier can eliminate the effect of ambient temperature and process on the output signal of detectors. The circuit was fabricated in a 0.35 m CMOS process under 5 V supply voltage. The Gm-C-OP integrated amplifier occupies an area of 0.012 6 mm2. The input differential voltage varied from 0 to 5 mV. Testing results show that the transconductance of OTA is in accordance with the simulation results. The Gm-C-OP integrated amplifier can convert the dynamic small input voltage into a proper voltage linearly and the linearity is 97%. The output range exceeds 2 V.
2016, 45(1): 104002.
doi: 10.3788/IRLA201645.0104002
Bundle adjustment is the key step in real-time mosaicking of remote-sensing imaging. It takes too much calculation time and decides the accuracy of the mosaicking system. Aiming at bundle adjustment algorithm in real-time mosaicking system of frame-sweep infrared imaging, a practical policy of bundle adjustment was proposed. The bundle adjustment between images of two adjacent sweep lines was used to register the lastest sweep line to the mosaicked image, which laid the foundation of real-time updating of mosaic image. The GPGPU platform was used to implement and accelerate, which improved the real-time performance of mosaicking system and also guaranteed the accuracy. By implementation of real-time bundle adjustment of frame-sweep images, the precision and real-time performance of the bundle adjustment algorithm were validated.
2016, 45(1): 104003.
doi: 10.3788/IRLA201645.0104003
Artificial infrared irradiation has an effective interference on correlation tracking by changing the infrared characteristics of target and background, where the location of infrared irradiation has an important impact on the interference performance. In order to improve the interference efficiency, the model of searching interference points by using infrared irradiation simulation was established. First, the infrared irradiation model in the true experimental environment was built in TracePro and the illuminance distribution of irradiation spot was fitted by Gaussian model. Then, the experiments with true irradiation condition and simulation irradiation condition were carried out. The comparison experiments show that the interference results of different irradiation locations under the two conditions are uniform in 98% and all interference points are found by irradiation simulation, illustrating the effectiveness of the proposed method in the paper.
2016, 45(1): 104004.
doi: 10.3788/IRLA201645.0104004
Aiming at the ship-target recognition of sea-sky background, an classification algorithm based on machine learning was proposed. In the method, the segmentation algorithm was firstly adopted to extract connected region in infrared image. Then, the corresponding position of the original image was marked and normalized. Afterwards, the high-dimensional feature vector of branded region by using the HOG algorithm was extracted. Finally, the high-dimensional feature vector that came form suspected target area was classified by the SVM classifier which was trained by sample library. Simulation experimental result indicates that the algorithm not only can effectively recognise the infrared ship-targets in complex sea-sky background of interference, but also have good performance.
2016, 45(1): 104005.
doi: 10.3788/IRLA201645.0104005
Photonic crystal defect formed by the introduction of the defect was amplified in the gain medium and formed laser. To further clarify the laser characteristics of the defect, the matrix of the photonic crystals was theoretically analyzed and the characteristics of the photonic band gaps was obtained: the width of the optical band gaps increased as the number of cycles does, and a certain value exceed a certain amount of cycles was reached; the higher the value which determined by the width of the optical band gaps constant, the higher refractive index ratio; superposing different centers of the photonic crystal wavelength can effectively expand the optical band gaps range. The experimental result from the band gaps analysis reveals one-dimensional photonic crystals in the KTP, which negatively affects the photonic band structure of the wavelength response curve; the refractive index of the KTP increases as temperature increases, and then the direction of the long wavelength defect mode changes. The results of this study contributes to the theoretical and practical development of small light sources.
WC/Co50 cladding coating was fabricated on 40Cr cutting tool surface by 6 kW transverse-flows multimode CO2 laser apparatus. The surface morphology, phase composition, microstructure, microhardness and wear behavior of the cladding coating were analyzed by optical microscope(OM), scanning electron microscope(SEM), energy disperse spectroscopy(EDS), X-ray Diffraction(XRD) hardness tester and friction wear testing machine. The results show that the original WC particles were dissolved greatly under the action of high-energy laser beam. The phase of coating is mainly composed of carbides WC, W2C,(Cr, Fe)7C3, W6C and Fe-Cr solid solution. The microstructure of WC/Co50 coating is complex, which consists of the primary dendrites, cellular eutectic, interdendritic eutectic and hard phase particles. The average hardness of the WC/Co50 coating is 1.93 times of the substrate, and the hardness of WC/Co50 cladding coating decreases with the increase of the surface depth. Under the same conditions, the wear weight loss of the composite coating is only 13.3% of the substrate.
2016, 45(1): 120002.
doi: 10.3788/IRLA201645.0120002
In order to meet the requirement of convex surface mask in concave surface lithography, convex surface laser direct writing system was set up to fabricate the mask. This apparatus supported up to 20 tilt angle. With the exposure correction algorithm in the process, the system accomplished writing rectangular grid pattern on a spherical substrate with 50 mm caliber and 51.64 mm radius. It was able to draw circular ring pattern on the surface by result of simultaneous motion of two tilting tables. The experiment shows that this setup has the capacity to fabricate the convex mesh lithographic mask and lay a solid base for convex surface lithography technology.
2016, 45(1): 120003.
doi: 10.3788/IRLA201645.0120003
The exposure time and signal gain can be used to adjust the light intensity for a conventional CCD camera,but both of them can not be configured best. It is also very difficult to maximize the effectiveness of their dimming, especially for the condition of the changed illumination intensity, the large dynamic range and the unclear picture.For the above-mentioned shortages, the histogram equalization certain improvements, the deployment of exposure time and signal gain were optimized through precise deployment of exposure time and optimization of signal gain coefficients. After the test, the screen effect has been significantly improved, the adjustment time is less than 40ms,and the system is stable and reliable.
2016, 45(1): 120004.
doi: 10.3788/IRLA201645.0120004
The flexural properties of Nomex honeycomb sandwich structure at different temperatures were studied with three-point bending method. Considering the honeycomb's orthotropy, L and W specimens were made, respectively taking the two main directions in the core plane as the longitudinal direction. Bending experiments were carried out to determine the bending stiffness and shear stiffness at 25 ℃, 50 ℃, 100 ℃, 150 ℃ and 180 ℃ respectively. The results show that both the bending stiffness and the shear stiffness in the two directions decreases as the temperature rises. When the temperature rises to 180 ℃, the two kinds of stiffness are less than 20% of that at room temperature. The temperature also has effect on the failure mode when the sandwich structure is under transverse mechanical load. A sunken skin is often seen when the temperature is below 50 ℃; when the temperature rises to 150 ℃ or higher, the skin may be separated from the honeycomb and be protruded outward. The research results may provide a reference for the application of Nomex honeycomb structure in laser irradiation or fluctuating temperature environments.
2016, 45(1): 120005.
doi: 10.3788/IRLA201645.0120005
Expandable graphite is the precursor to preparate exfoliated graphite(EG). Confectioning by compressed column will have an impact on the laser extinction performance of EG exfoliated from it. In order to optimize the performing parameter, a series of preformed graphite intercalation compound (GIC), as the precursor of EGs, were prepared under different performing pressure. And the expanding state, expanding volume (EV), micro-morphology and laser extinction of the EGs obtained from the performed GICs were studied. Experimental results show that compared with the diameter, length and porosity of the EG decrease, and the layers of preformed GIC open deficiently. With the increase of performing pressure, the EV of GIC decreases from 356 ml/g to 216 ml/g, and meanwhile, the laser mass extinction cross section(M) of EG obtained from GIC decreases from 0.18 m2/g to 0.04 m2/g. But both values of EV and M drop more slowly at 20-40 MPa, and therefore, it is considerable for a high loading density to choose the upper value of 20-40 MPa as the performing pressure on GIC in EG practical application.
2016, 45(1): 122001.
doi: 10.3788/IRLA201645.0122001
In fiber optic gyroscope using low-polarization and polarization-maintaining hybrid light path, some single mode fiber components and single mode fiber(SMF) are contained. When SMF bends, the transmitted core-guided mode light and whispering gallery(WG) mode light in SMF interfere with each other, and then affect the transmitted light. A model of the influence of SMF bending on FOG scale factor stability was developed and demonstrated. Simulation and experimental results indicate that the SMF bending can lead to the transmitted light mean wavelength drifting and oscillating under temperature ramping, furthermore leads to FOG scale factor instability. The mean wavelength oscillation amplitude depends on the bending radius.
2016, 45(1): 122002.
doi: 10.3788/IRLA201645.0122002
The influence of retro-reflect modulation reflected optical characteristics on the retro-reflect modulation structure parameters and receiving distance were studied by establishing off-focus structure equivalent model of retro-reflect modulation, and the theory of retro-reflect modulation model with geometrical optics method was analyzed. Some expressions related to the structure was given, numerical calculation and experiment were completed. Results show that the retro-reflect modulation structure parameters and receiving distance affect the variations of modulation system reflection power boviously and regularly. Moreover, reducing the lens focal length, increasing the lens aperture and increasing the receiving distance can increase the rate of change, and make contribution to improve the modulation effect. And under normal circumstances, the divergence of the reflected beams is much smaller when the mirror in the focal plane moves forward out of focus.
2016, 45(1): 122003.
doi: 10.3788/IRLA201645.0122003
In order to improve the disturbance isolation degree for space optical communication Pointing, Acquisition, and Tracking(PAT) system, a novel control method based on disturbance observer was proposed. Firstly, according to the structure analysis of PAT system, the simplified system model was gained and then the disturbance was observed from the position of the motor and the laser spot by disturbance observer. Finally, the equivalent amount of disturbance compensation was added to the integration points in front of the current loop. The simulation results of fine tracking system show that compared with the traditional PD controller, adding the disturbance observer can improve the disturbance isolation degree at almost all frequencies before the motor current saturates, and the optimal situation has reached 28.2 dB. Meanwhile, this method has strong robustness; the disturbance isolation degree still increases by at least 1 times than not using the disturbance observer when there are 15% changes for the system physical parameters. The proposed control method greatly improves the disturbance isolation degree for PAT system and is of certain reference value to the wide range and high dynamic precision photoelectric tracking system.
2016, 45(1): 122004.
doi: 10.3788/IRLA201645.0122004
A demodulation system based on 256 pixels linear array InGaAs detector for fiber Bragg grating sensors was researched and realized. Based on the linear array InGaAs detector, the peak positioning principle of the fiber Bragg grating reflection spectrum was put forward. This multiple FBG spectrum parallel processing could be realized. The demodulation quantity of single channel depended on the bandwidth of the FBG sensor and the center wavelength drift range. Based on the spectral data of 256 pixels, Gaussian curve model for central wavelength was adopted. By setting the threshold value, the number of reflection spectrum peak was obtained, separately for each spectrum peak fitting. The demodulation technique was proved to be highly accurate and highly stable by the experiment results. The stability of peak searching algorithm reached 0.5 pm. The demodulation method has no mechanical moving parts, which realizes the parallel processing and quick response of the fiber Bragg grating center wavelength. The wavelength demodulation range is 1 525-1 570 nm. It provides a high-speed demodulation scheme for fiber Bragg grating sensing.
2016, 45(1): 122005.
doi: 10.3788/IRLA201645.0122005
Coupling of scattering light in space into fiber has also been used widely in many fields. However, when the scattering objects is big, how to coupling of scattering light in space into fiber efficiently is seldom studied. Considering that coupling efficiency and the field of view are important parameters of a fiber optic based receiver, the coupling efficiency with different axial and racial offsetting or different input angles was analyzed, then the coupling efficiency and field of view of the fiber optic receiver was compared by theoretical analysis and emulation.
2016, 45(1): 122006.
doi: 10.3788/IRLA201645.0122006
In order to analyze the maximum Raman gain of forward-pumped and backward-pumped fibre Raman amplifier(FRA), by theoretical derivation method for solving the differential coupling equations, the formulas for the maximum Raman gain of forward-pumped and backward-pumped FRA were defined and obtained based on different signal amplification process with different pumping structure. Using these new formulas, the effects of input signal power, input pump power, Raman gain coefficient per area, fibre attenuation and the pump to signal frequency ratio on the maximum Raman gain of forward-pumped and backward-pumped FRA were investigated in detail in the condition that the parameters were all of their typical values. Some results are consistent with results of involved references. Besides, maximum Raman gains of two pumping ways under the same parameter were compared. Finally, maximum Raman gain and on-off gain which was frequently-used were compared. These results are creative and helpful to the experiment study of FRA.
2016, 45(1): 117001.
doi: 10.3788/IRLA201645.0117001
In order to realize the coordinate measurement of hidden parts in the large-scale space, a combined non-contact measurement system which combined attitude angle sensor, angle encoder, laser rangefinder and total station, was proposed. A mathematical model of the measurement system was established. The calibration target was designed and the measurement system was calibrated. For the measurement system, a calibration method based on the weighted least squares was proposed and the weight value was determined according to the spatial distribution of the control points. The precision of the combined system was verified by comparing the error of the same test point between the spatial coordinate measured directly by the total station and that of measured indirectly by the combined system. Experimental results show that the measurement system could expand the scale and achieve reliable precision during combined measurement and the measurement error of the weighted least squares method is smaller than that of the general least square method.
2016, 45(1): 117002.
doi: 10.3788/IRLA201645.0117002
In order to realize the non-contact measurement of the energy and the characteristics of jamming bomb, the research on energy measurement device based on infrared radiation type jamming bomb was carried out. Firstly, jamming energy and radiation characteristics of the band were summarized; then, the energy and characterization were characterized with infrared radiation energy level; and then, based on the above theory, energy measurement of infrared radiation was simulated and developed, including choosing and apply design of detectors, analogue signal processing and digital signal processing, detecting and calculating energy with relative detecting methods. At last, the specific realization methods and advantages of the infrared measuring device were introduced. The experiment result shows that the response time of the infrared radiation energy measurement device is less than 2.5 ms, and detection sensitivity is better than 2.5108 cmHz1/2W-1. Energy measurement system based on infrared radiation type successfully implements the accurate measurement of long wave infrared energy to the 1-21 m with higher sensitivity and lower response time.
2016, 45(1): 117003.
doi: 10.3788/IRLA201645.0117003
The noise figure is an very important factor which can limit the detection capability of the photoelectric detection circuit. To solve the problem, a photoelectric detection circuit was designed in the condition of the photodiode reverse bias, and then the circuit noise was analyzed indetail. When analyzing the noise, the structure of the photoelectric detection circuit was focused on. The whole circuit could be equivalent to three cascade module which were the photodiode module, the triode module and the operational amplifier module. Then, the noise source and the associated factors of each module were analyzed, and the output noise voltage of each module was calculated. Finally, the output noise voltage model of the whole circuit could be obtained. At last, the parameters of the whole circuit were determined according to the module, the circuit was built, the noise of circuit was measured, the accuracy of the output voltage model was verified. It realizes the design of photoelectric detection circuit.
2016, 45(1): 117004.
doi: 10.3788/IRLA201645.0117004
Due to the effect of atmospheric refraction, the space objects (e.g. stars, aircraft, and so on) observed from ground-based optoelectronic telescopes always have positions that different from their actual ones. The lower the elevation of the space objects, the more obvious the effect of atmospheric refraction becomes, and hence the larger position difference will be deduced. To position the space objects with high accuracy, it is necessary to correct the effect of atmospheric refraction. In order to improve the correction accuracy of atmospheric refraction effect during the observation of space objects with low elevations, the correction curves of atmospheric refraction effect were obtained by retrace-scanning fixed stars in the neighborhood of the orbit of space objects, based on the original model for correcting and computing the effect of atmospheric refraction. At last, through large amount of experimental demonstration and polynomial curve fitting, a new expression was proposed for the correction of atmospheric refraction effect with low elevation observation. The computation results from several experiments show that, during the observation of mission space objects with infrared long-wavelength system, the initial elevation reduced to 2 from 10, the capture time for the mission space objects with infrared long-wavelength brought forward more than 50 s, and the critical characteristic points(e. g. assembly separation) of the mission space objects could be observed. The experimental results indicates that, our proposed method can be used to reduce effectively correction error of atmospheric refraction effect with low elevation observation, to improve the capability and accuracy in the process of capturing and tracking the mission space objects with infrared long-wavelength systems, and has great worth in actual engineering and practical application area.
2016, 45(1): 117005.
doi: 10.3788/IRLA201645.0117005
In order to evaluate the roundness error of large-scale sleeve, a roundness error measurement system of large-scale sleeve was established and its applied algorithms such as laser collimation, image processing and etc were investigated. First, the method that the system obtained roundness error of large-scale sleeve was introduced. Then, based on the measuring process, a filtering algorithm of minimum circumscribed circle which analyzed the point position forms was presented. Finally, filtering efficiency was analyzed. Computing time and the precision were compared with the similar algorithm. Experimental results indicate that the computing time of the filtering algorithm is shorter by more than 30% and the precision of the CCD measurement rod is 0.7 mm. The roundness error measurement system of large-scale sleeve can satisfy the requirement of the project and evaluate roundness error effectively.
2016, 45(1): 117006.
doi: 10.3788/IRLA201645.0117006
When the reflection mirror component is assembled for topography measurement, the manufacturing tolerance of parts, including dimensional tolerance, contour tolerance could cause assembling stress, which induces to descend of surface figure accuracy. In order to resolve the problem, a method of applying flexure hinge in the design of reflection mirror component measurement tooling was proposed. To verify its reliability, using flexure hinge theory and finite element analysis software, considering the characteristic parameters and verifying method of the reflection mirror component, the reflection mirror topography measurement tooling was designed and manufactured. The reflection mirror component repetition topography measurement, the sensitivity tightening torque topography measurement test were taken respectively, which proved that the flexure tooling has well stability. Compared with the single reflection mirror, the surface figure of component changed 0.006 rms, which satisfied the requirement of tooling design. Using flexure hinge in reflection mirror component topography measurement is better in reducing assembling stress than rigidity tooling.
