Laser technology
2019, 48(1): 105001.
doi: 10.3788/IRLA201948.0105001
An electro-optic (EO) Q-switched Nd:YVO4 laser with high repetition rate, end-pumped by continuous-wave (CW) laser diode (LD) was reported. Using RbTiOPO4 (RTP) single crystal as an EO Q-switch, by matching mode of oscillation light and pump light, 1 064 nm laser output with high efficiency, high repetition and short pulse width was realized. On the one hand, low absorption coefficient of 914 nm wavelength was adopted to pump Nd:YVO4 crystal, so that the heat distribution inside the crystal was uniform, thereby achieving high quantum efficiency while reducing the thermal effect. On the other hand, the pump light spot radius was optimized to match mode of pump light and oscillation light. At the repetition rate of 200 kHz, the maximum average output power of 16 W, full width at half maximum of pulses of 9 ns, single pulse energy of 80 J and beam quality M21.2 are achieved at an absorption pump power of 31 W, corresponding to an optical conversion efficiency of 51.6%. To the best of our knowledge, this is the highest efficiency reported on the EO Q-switched laser by using RTP crystals.
2019, 48(1): 105002.
doi: 10.3788/IRLA201948.0105002
Aiming at the mechanism of catastrophic optical damage of semiconductor laser cavity surface, a single-chip semiconductor laser cavity surface vacuum cleavage passivation process was designed. The cleavage process in vacuum and direct evaporation of passivation film on the surface of semiconductor laser cavity was proposed. Using ZnSe material as the passivation film material for the vacuum cleavage process of single-die semiconductor laser, it was found that the vacuum cleavage passivation process and ZnSe material could be used as the passivation film to increase the output power of the device by 23%. The mechanism of semiconductor laser cavity surface damage was analyzed by electroluminescence (EL). It is further explained that the introduction of vacuum cleavage passivation technology in the preparation process of 915 nm semiconductor laser and the selection of ZnSe as the passivation film can effectively protect the cavity surface of the semiconductor laser and improve device reliability.
2019, 48(1): 105003.
doi: 10.3788/IRLA201948.0105003
In recent years, with the increasing demand for optoelectronic technology applications, more and more fields such as Plane Laser Induced Fluorescence, laser detection and laser processing have shown the demand for high-repetition-rate and high-energy pulsed lasers. However, due to the limitation of average power, it is difficult for the conventional continuous pulsed lasers to achieve pulsed laser output with high repetition rate and high energy. In this paper, an LD-pumped 1.06 m Nd:YAG burst-mode laser and its amplification system were studied and demonstrated. By employing long pump duration, burst-mode technique, and MOPA amplification scheme, the laser output with high repetition rate and high energy was obtained in the burst duration. After dual-stage amplification, the burst energy reached 170.4, 211.8, and 220.3 mJ at Q-switching repetition rate of 10, 50, and 100 kHz, containing 2, 12 and 25 pulses in one pump duration, respectively. The single pulse energy reached 85.2, 17.7, and 8.8 mJ, respectively.
2019, 48(1): 105004.
doi: 10.3788/IRLA201948.0105004
In order to make the laser with V-resonator have good output performance, it is necessary to find the influence rules of cavity parameters on the laser output performance in laser cavity design. Combining the graphic analysis method of V-type folded cavity and the equivalent cavity analysis method of multicomponent optical resonator, the stability of the equivalent coaxial spherical cavity and the output laser beam quality were theoretically solved and analyzed after equivalent approximation of the folded cavity. The internal relationship between the V-type folded cavity parameters and the laser output performance were found. By calculating the given conditions, some results were known. The ideal value range of total cavity length L is 70-80 mm with the optimal value 75 mm when the folding angle is equal to 0.15. The allowable variation range of curvature radius of end mirrors R1 and R2 is 60-80 mm. And the curvature radius of of folding mirror R3 has a minimum value of 45 mm. The laser spot radius and the far-field divergence angle of fundamental mode on the right (left) end mirror will become larger with the increase of g-parameters of left (right) subcavity. The above-mentioned equivalent cavity analysis method and the achieved results can provide an important reference theoretically for the cavity optimization design.
2018, 47(5): 505001.
doi: 10.3788/IRLA201847.0505001
A high-power high-efficiency narrow-bandwidth thulium-doped fiber laser (TDFL) with output wavelength 1 915 nm was studied in this work. The thulium-doped fiber laser was based on system of master oscillator power amplifier (MOPA). The laser diode with about 40 W output power and 793 nm wavelength was used to pump double cladding large-mode-area (LMA) thulium-doped fiber with 25 m core diameter, the narrow-bandwidth continuous wave(CW) seed laser with wavelength 1 915 nm and maximum power 12.1 W was obtained. When the 793 nm pump power was 142.9 W, after the 8 W seed laser going through the thulium-doped fiber amplifier, the output laser had average power of 90 W, central wavelength of 1 915.051 nm, and the 3 dB spectrum bandwidth was 94 pm, with slope efficiency of 60%, and optical-to-optical conversion efficiency of 63%. The stability of output laser of this system behaves well in the 40 min operation checking time.
2018, 47(5): 505002.
doi: 10.3788/IRLA201847.0505002
Aiming at the problem of wide pulse pedestal and lower pulse energy of passively mode-locked fiber laser based on Semiconductor Saturable Absorber Mirror(SESAM), a double SESAM passively mode-locked ultrashort pulse fiber laser based on linear cavity structure was designed. Firstly, through increasing the number of SESAM, the optical pulse would pass through the SESAM repeatedly in one oscillating period in the cavity, the absorption of the absorber was improved to the pulse front and back edge, the Q mode-locked effect due to larger pump power was suppressed, contributed to pulse compression and raised the single pulse energy, the effect of the SESAM lower modulation depth on the pulse width and single pulse energy was eliminated. Secondly, the introduction of positive dispersion in the system could reduce the nonlinear effect caused by the peak power, and further improving the pulse energy. Finally, compared with the single SESAM mode locking under the same modulation depth and saturation flux, the output pulse width of the double SESAM mode-locked fiber laser shorted 35.2%, from 693 fs to 449 fs, and the single pulse energy raised 45%, from 2.92 nJ to 5.31 nJ.
2018, 47(5): 505003.
doi: 10.3788/IRLA201847.0505003
A passively continuous-wave(CW) mode-locked Tm:YAP laser with a semiconductor saturable-absorber mirror was reported by using laser-diode as pump source. According to the ABCD matrix theory, the astigmatism and the stability in the cavity of the laser were theoretically analyzed. Stable continuous-wave mode-locked ps-pulses were achieved. The average output power of 0.73 W was obtained with the absorbed pump power of 7.96 W and the corresponding slope efficiency was 15.6%. The pulse duration was measured to be 1.7 ps with a repetition rate of 88.7 MHz at the central wavelength of 1 982.4 nm, and the corresponding slope efficiency was 15.6%. The results show that the Tm:YAP crystal has good thermal mechanical properties, which is very favorable for generating ultrashort pulses at around 2 m.
2018, 47(5): 505004.
doi: 10.3788/IRLA201847.0505004
In order to meet the requirements of infrared gas detection for high performance laser driving power supply, the PID control algorithm was adopted, a high stability DFB laser driving power supply was designed and manufactured. Its hardware mainly included signal generation module, voltage-controlling current source module, circuit protection module. The system had the function of output current protection. In the signal generation module, the sine wave was generated by DDS and then square waves was generated through a comparator. At the same time, DA conversion technique was adopted to realize the output of DC wave, triangular wave and sawtooth wave. Meanwhile, in respect of control scheme, the current high stability was effectively ensured by the use of PID control algorithm and veep negative feedback. With this driver, the driving test was performed on a DFB laser with a center wavelength at 1 563.09 nm. The results show that the driver has the function of the output waveform type, amplitude and frequency can be changed by digital control, the current amplitude ranges from 0 to 1 A and the frequency range is from 1 Hz to 1 MHz. The frequency resolution is 1 Hz. The linearity of the system is 99.93% and the long term output current stability reached 0.019 7%.
2018, 47(11): 1105001.
doi: 10.3788/IRLA201847.1105001
High power single frequency fiber lasers are extensively applied in coherent detection and power spectrum beam combination etc. The suppressing method of stimulated Brillouin scattering was analyzed. The influences of amplification level on stimulated Brillouin scattering were studied. A single frequency fiber laser with linewidth of 70 kHz was used as seed source. And through two stage amplified, the central wavelength of 1 064.1 nm, linewidth of 70 kHz and power of 180 W were achieved respectively. The optical-optical efficiency is 71.1%. And the beam quality is Mx2=1.2 and My2=1.21. The output power before and after changing amplifier characteristic was compared. And the reason that output power increased was analyzed. The stimulated Brillouin scattering gain coefficient was reduced by varying amplifier temperature distribution. Then stimulated Brillouin scattering threshold was promoted. Finally, this makes the output laser power increase greatly after varying amplifier temperature distribution. The output power of this laser is only limited by pump power. If the pump power is increased, the higher power of single frequency all fiber laser will be achieved.
2018, 47(11): 1105002.
doi: 10.3788/IRLA201847.1105002
With the rapidly increasing applications of high power laser diode(HPLD) in extreme environments, the reliability of bonding interface has become one of the critical bottlenecks affecting the HPLD's performance and lifetime. In this work, failure behavior and lifetime of a single-bar CS-packaged HPLD under -55-125℃ thermal-shock were analyzed by finite element method(FEM). Based on Anand constitutive model and Darveaux energy accumulation theory, the reliability of indium bonding layer on the edge and at the central position after the themal-shock was compared. It shows that the bonding interface on the edge has the highest stress (0.042 5 GPa) and lowest lifetime (3 006 cycles), in other words, the edge is the riskiest element of the bonding interface. In addition, the lifetimes of three kinds of bonding layers on the edge, including indium, 80Au20Sn and nanosilver paste, were simulated to be 3 006, 4 804 and 4 911 cycles, respectively. The results show nanosilver paste and 80Au20Sn have longer lifetimes and better reliability, which are better bonding materials in the packaging of high power laser diodes used in extreme enviroments.
2018, 47(11): 1105003.
doi: 10.3788/IRLA201847.1105003
The double wavelenghs short pulse laser was developed with the high mode volume and variable reflectivity mirror(VRM). The thermal lens and the thermal birefringence produced by diode-lasers pumped rod laser medium was compensated, which presented a short-pulse energy of 140 mJ and 1 064 nm laser output with a pulse width of 17.76 ns at a repetition rate of 500 Hz. The beam quality value was M21.6, and the energy instability(RMS) value of 20 minutes was less than 0.3%. The result of resonator was corresponded with Master Oscillator Power-Amplifier(MOPA) technology, but it was close and neat. The maximum laser energy of 96 mJ at 532 nm was demonstrated by extra-cavity second-harmonic generation(SHG) with type-Ⅱ angle phase-matched GTR-KTP crystal, the KTP crystals with resistance to grey trace effect was grown by hydrothermal method. The maximum efficiency of SHG was 68.6%, and the beam quality value was M22.1. The 1 064 nm and 532 nm laser were output at same axis with energy regulation.
2018, 47(11): 1105004.
doi: 10.3788/IRLA201847.1105004
Influences of the bias states of saturable absorbers on bistable InGaAsP multi-quantum-well(MQW) common cavity tandem section(CCTS) semiconductor lasers were investigated experimentally and theoretically. The experiment demonstrated that the bistability characteristic of P-I curves can be more significant with increasing reversed bias voltage in the saturable absorber(SA), and a negative differential resistance phenomenon was found in V-I curves. When the voltage was -3 V, the hysteresis width was broadened to 13.5 mA, with the on-off ratio up to 21:1. The theoretical analysis proves that higher passive voltage in SA and shorter carrier escape time can result in better bistability. The maximum on-off ratio as high as 107:1 promises that a common cavity two-section laser can be switching between the two-steady state.
2018, 47(11): 1105005.
doi: 10.3788/IRLA201847.1105005
The theoretical analysis and experimental study of the instability phenomenon of a Nd:YAG Q-switched short pulse laser was demonstrated. During the operation of the short pulse laser, there were many factors that can cause the instability phenomenon. During the experiment it was found that the interference pulse which can enter into the cavity though the output mirror can cause the instability of the short pulse laser. Based on the basis of thory, the influence of external interference light on the output light characteristics of short pulse Q-switched laser was simulated and verified by experiments.The characteristics of energy and pulse width were discussed respectively. The results show that the greater the energy of interference pulse is, the more serious the instability phenomenon is. When the interference pulse energy is 60 mJ, the loss of output energy of the short pulse laser can be more than 15%. The pulse width is 1.15 times of the original, the instability phenomenon is also more serious at the pump end of the short pulse Q-switched later. When the input energy is 60 mJ the pulse width is 10 ns, the loss of output energy of the short pulse Q-switched laser reaches 80% of the original.
2018, 47(11): 1105006.
doi: 10.3788/IRLA201847.1105006
Influence factors of compactness of DF laser with cooling gas ejector were analyzed. Ratio of Laser Power to Gas Source Volume(RPGV) was chosen as DF laser compactness evaluation index and was calculated at different conditions. According to the result, RPGV increases at first, and then decreases with increasing nozzle array mass flux. RPGV gets maximum value when nozzle array mass flux is about 3.3 gs-1cm-2. In the case of same laser effluent parameters, increasing ejector driving gas total pressure leads to a bigger RPGV, but its effect on RPGV gradually becomes weak. Compared with helium as ejector driving gas, adopting nitrogen and air as ejector driving gas leads to higher RPGV.
2018, 47(11): 1105007.
doi: 10.3788/IRLA201847.1105007
Crystalline Raman amplifier is an important way to obtain high beam quality, high spectral purity and high power Raman laser. The normalized transport equations of the external cavity Raman amplifier were derived by inducing four normalized composite parameters. A set of universal theoretical curves describing the operation of Raman amplifiers were obtained by numerical solving the transport equations, and the influence of the complex normalized variables on the performance of the Raman amplifiers was analyzed. The dependences of the magnification of the Raman pulse peak intensity, pulse shape of the output Raman laser, and the conversion efficiency from pumping laser to output Raman laser on the pumping pulse intensity, the relative width of the pumping pulse and Raman seed pulse, and the time overlap of the pumping pulse and Raman seed pulse were studied in detail. The optimum working condition of crystalline Raman amplifier was explored. The normalized theory was verified with actual experimental data. It is indicated that the theoretical results are consistent with the measured data. The normalized rate-equation model is proved to be precise and feasible.
2018, 47(11): 1105008.
doi: 10.3788/IRLA201847.1105008
A compact, intra-cavity widely tunable continuous-wave singly resonant optical parametric oscillator (SR-OPO) was reported based on a MgO-doped periodically poled lithium niobate (MgO:PPLN). A diode-pumped Nd:YVO4 laser at 1 064 nm was employed as the pump source of this SR-OPO with a compact linear cavity. The MgO:PPLN crystal used contained seven different periodically poled gratings from 28.5 to 31.5 m with a step of 0.5 m between the neighbor periods. The output wavelengthes at the different grating periods of MgO:PPLN crystal was measured, which was well matched with the theoretical value. The widely tunable SR-OPO output signal wavelength range from 1.43 to 1.67 m and idler wavelength range from 2.93 to 4.16 m were achieved. The output power as the function of grating periods and pump power was investigated. Under an incident pump power of 14.5 W, a maximum signal output power of 2.94 W at 1 595 mm and an idler output power of 1.45 W at 3 190 nm were obtained with the temperature controlled at 35℃ and the period set at 31 m. The diode to OPO total output conversion efficiency reached 28.5%.
2018, 47(11): 1105009.
doi: 10.3788/IRLA201847.1105009
Heat seeking weapons such as man-portable air defense system (MANPADs), various IR guiding missile are the main threaten for civil aircraft and military aircraft. As the appearance of IR imaging seeker, the effect of traditional IR interference equipment and infrared flares are limited. Otherwise, direct IR countermeasure (DIRCM) system has been effective means. In this paper, the international research on DIRCM and key techniques for laser of DIRCM was reviewed. Furthermore, calculating method for dazzling area of imaging detector was given. At the same time, the research trends of DIRCM and laser of DIRCM were forecasted in the future.
2018, 47(10): 1005001.
doi: 10.3788/IRLA201847.1005001
Lasers in the 3-5 m waveband have many important scientific and military applications such as remote sensing, environmental protection, medical treatment, communication and infrared countermeasures. Fe2+:ZnSe crystal has become one of the most promising materials to generate laser in this region due to its advantages in material and optical properties. The characteristics of a polycrystalline ZnSe sample, which diffusion-doped with Fe2+ ions at a concentration of 31019/cm3, were investigated. The diameter and the thickness of the sample were 10 mm and 1 mm, respectively. The output characteristics of the Fe2+:ZnSe laser, which was excited by a non-chain electric-discharge pulsed HF laser, were studied at room temperature. A mid-infrared laser with the maximum output energy of 78.8 mJ at a center wavelength of 4 295 nm was obtained. The efficiency respecting to the absorbed pump energy was 27.7% and the slope efficiency was as high as 28.8%. The Fe2+:ZnSe laser was pumped at a small angle (3) with respect to the optical axis of the laser cavity instead of orthogonal-pump. It solved the problems that a HF laser and a Fe2+:ZnSe laser are both in the mid-infrared band.
2018, 47(10): 1005002.
doi: 10.3788/IRLA201847.1005002
At present, 1.5 m LD pumped Er-glass passively Q-switched micro-laser is a popular research direction in military laser ranging. Achieving high repetition rate and single pulse energy are very important indicators. In this paper, a kHz erbium-ytterbium co-doped phosphate glass passively Q-switched microchip laser for laser ranging was reported. The laser was pumped by a single diode with a center wavelength of 940 nm and erbium-ytterbium co-doped phosphate glass (Er3+,Yb3+:glass) as the gain medium, CO2+:MgAl2O4 (CO:MALO) as the saturable absorber. By analyzing the influence of the pump spot radius on the mode-matching, the pump spot radius was optimized. The effects of the initial transmittance (T0) of saturable absorber and the reflectance R of output mirror on the output laser parameters were experimentally analyzed. In the final pre-pumping experiment, a Q-switched pulse was achieved, with repetition frequency of 1 kHz, wavelength of 1 535 nm, single pulse energy of 40 J, pulse width of 5.09 ns, peak power of 7.89 kW and beam quality of 1.4.
2018, 47(10): 1005003.
doi: 10.3788/IRLA201847.1005003
In order to solve the output wavelength and power stability of high power semiconductor laser, high power semiconductor laser constant current driver and temperature control system were designed. Deep negative feedback circuit was used to control the laser drive current, the analog Proportional-Integral (PI) circuit and constant current driver were adopted to control the working current of Thermoelectric Cooler (TEC), the laser working temperature can be kept accurately. The design can realize the linear adjustment of output current from 0-12.5 A, and has the function of current detection, over-current protection and Transistor-Transistor Logic (TTL) modulation. The control precision of the temperature control system can achieve 0.05℃. Temperature can be adjusted continuously and can be monitored in real time. Experiment results show that the design can guarantee the output current and temperature control stably, which satisfies the requirement of high power semiconductor laser.
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