Lasers
2019, 48(S1): 50-55.
doi: 10.3788/IRLA201948.S105001
By combining a large mode area(LMA) Yb-doped double cladding fiber(YDCF) amplifier with a solid state seed laser, an fiber amplifier, whose single pulse power was about 1 mJ and narrow linewidth was about 0.1 mJ, was reported. Different from the traditional one-stage fiber amplifer with solid state laser seed source, a two-stage large diameter fiber amplifer was used in the YDCF amplification system. The two-stage fiber amplifer was much simpler in the aspect of coupling the spatial seed light into the fiber. A variety of methods were used to suppress nonlinear effects during the amplification process. Obvious nonlinear effects such as SBS, SRS, were not observed in the output, with the SNR exceeding 30 dB. After YDCF amplification system, the output average power was amplified to 10.07 W. Compared to the power of seed, which was about 0.38 W, the output was increased by 14.23 dB. At the pulse repetition rate of 10 kHz, the pulse energy is about 1 mJ, with the pulse width of 50 ns. The beam quality M2 of the output laser is 3.72. The pulsed fiber amplifier with narrow linewidth and high pulse energy will be very useful in many practical applications, such as laser remote sensing, laser measurement and nonlinear frequency conversion and so on.
2019, 48(S1): 56-63.
doi: 10.3788/IRLA201948.S105002
Based on the three-level rate equation, a simulation model of the end-pumped K vapor laser threshold was established, and the threshold characteristics of diode pumped K vapor laser was analyzed. The influences of operation parameters on the threshold pumped power intensity were investigated, which was based on this model. The result shows that cell's temperature and length both govern the distribution of populations of K, thus combining to impact on the threshold pumped power intensity, and there exists optimal temperature and length. The threshold power intensity linearly increases with pump linewidth. The buffer gas pressure impacts on the threshold intensity by changing the cell's absorption efficiency of the pumped power. High window transmittance and less than 70% output coupling can make threshold keep in a lower level. The study for various parameters of components will provide reference for the design and optimization of the systems, and diode pumped potassium vapor laser output.
The accelerated aging test of 60 W(CW mode) 808 nm indium-packaged conductively cooled single bar high power semiconductor laser with constant current under three different temperatures was analyzed by Weibull and Log-normal distributions models, respectively. The characteristic lifetime and statistical average lifetime of the device under all the tempertures including room temperature were calculated in Weibull distribution analysis, and it is found that for early failure test, the shape parameter is less than 1, and the calculation error of mathematical average lifetime is larger, which is not as good as statistical average lifetime. In Log-normal distribution analysis, the medium lifetime and statistical average lifetime under all the tempertures are calculated. It is found that for early failure test, the logarithmic standard deviation is larger and creates larger error of statistical average lifetime. It means that Log-normal distribution mode is not suitable for lifetime estimation of early failure device. Finally failure analysis of accelerated lifetime devices is carried out.
2019, 48(4): 405001.
doi: 10.3788/IRLA201948.0405001
The control precision and stability of emitting wavelength of distributed feedback laser directly determines the measurement accuracy of detection system that uses infrared distributed feedback laser excitation light source as the core section. A temperature control system of distributed feedback laser was developed utilizing analog PID control. Simulated proportional-integral-differential temperature forward control module and real-time temperature backward acquisition module were adopted to control temperature. Emitting wavelength of 2 049 nm DFB laser was used in temperature control experiment. Results show that system temperature control stability is 0.05℃, and the stability time is less than 30 s. Meanwhile, spectrum test experiment was conducted using the developed temperature control system to control the proposed distributed feedback laser. The results show that the emitting wavelength of laser is linear with its working temperature while the laser drive current is fixed.
2019, 48(4): 405002.
doi: 10.3788/IRLA201948.0405002
In order to study the influence of pump bandwidth and wavelength-drift on the performance of solid-state lasers, theoretical analyses were performed on a quasi-three-level Tm:YAG laser, and the corresponding theoretical models, including both spectral and thermal models, were presented. In the Tm laser experiment, a compact and high-efficiency composite Tm laser operating at 2 013.2 nm was demonstrated, which was end-pumped by volume Bragg gratings(VBGs) locked laser diode(LD) with emission wavelength centered at 784.9 nm and bandwidth as narrow as 0.1 nm(full width at the half maximum, FWHM). A maximum output power of 7.96 W was obtained with a slope efficiency of 62.5% and optical conversion efficiency of 53.3%, respectively. The maximum laser wavelength drifted from 2 013.25 nm to 2 014.53 nm when increasing the absorbed pump power from 1.87 W to 14.93 W for the 3% output coupling. As for 5% output coupling, the drift was from 2 013.91 nm to 2 014.26 nm. It was found that a narrow LD bandwidth of 0.1 nm resulted in a more pronounced excitation efficiency and thus a higher laser efficiency, despite that the maximum temperature within the crystal was slightly higher. The present study could be extended to other solid-state lasers for the choice of pump source by comprehensively considering the pump bandwidth and wavelength-drift and the spectral profiles of gain medium, which would be helpful for an efficient laser system.
2019, 48(4): 405003.
doi: 10.3788/IRLA201948.0405003
A passively Q-switched human-eye safety micro-ranging laser with a double-end bonded composite structure was reported. The double-end bonded structure was formed by the heterogeneous material composite technology, including the gain medium Er3+/Yb3+:glass, F2 glass and passively Q-switched crystal Co2+:MgAl2O4. The output characteristics of the double-bonded composite structure and the non-composite structure were compared in the experiment. The former laser performance parameters are significantly better than the latter. The double-bonded composite structure achieved a human eye-safe laser output of pulse energy 330 J, beam quality 1.4, pulse width 5.5 ns with 10 Hz repetition frequency; the non-composite structure laser had a single pulse energy 245 J, pulse width 6.5 ns, and the beam quality 1.9. The thermal simulation of double-bonded composite structure gain media and monolithic Er3+/Yb3+:glass shows that the former has a 51.2% increase in thermal focal length relative to the latter, and the thermal effect of the double-bonded composite structure is significantly improved. The above shows that the double-bonded composite technology can reduce the temperature gradient inside the gain medium, make the thermal focal length longer, increase the volume of the mold, and improve the mode matching of the oscillating light and the pump light, so that the single pulse energy is increased.
2019, 48(4): 405004.
doi: 10.3788/IRLA201948.0405004
The operating wavelength of a semiconductor laser(LD) varies with temperature. Temperature control of a LD was a common method of extending the normal operating temperature range of an all-solid-state laser(DPSSL). However, commonly used methods have large volume, high energy consumption and low efficiency in the wide temperature range of -50℃ to 70℃. The wavelength drift coefficient of the GaAs quantum well laser is 0.25 nm/℃, and the multi-peak characteristic of the absorption spectrum of Nd:YAG crystal was analyzed. A GaAs quantum well laser with a working wavelength of 808 nm at high temperature was used as the pump source. The two absorption peaks of 795.7 nm and 808 nm of Nd:YAG crystal were used to reduce the temperature control power consumption by segment heating. The experimental results show that the output pulse characteristics of the DPSSL at the two absorption peaks are basically the same. At lower temperature, the heating power of the segmented temperature control is reduced by 4.7 W, which is close to half of the maximum heating power without segmentation.
2019, 48(4): 405005.
doi: 10.3788/IRLA201948.0405005
The high energy pulse width tuning 1 064 nm solid-state laser was developed by adopting MOPA laser source and combining the traveling wave amplification of xenon-lamp pumping. The pulse signal out of MOPA fiber laser was controlled by the method of electric modulation pulse width. Under the premise of ensuring high beam quality, a 1 064 nm laser source output with pulse width of 8.6-220.9 ns was achieved. Adopting double pass amplifier design, five-step travelling wave amplification was achieved by xenon lamp pumping Nd:YAG crystal. The technique of restraining self-oscillations and the reasons of narrowing pulse width in the process of traveling wave amplification were analyzed. When the inject energy of xenon-lamp was 60 J and the repetition rate was 10 Hz, a 1 064 nm laser output with pulse width of 4.2-173.3 ns was achieved. Single pulse energy was up to 158 mJ.
2019, 48(4): 405006.
doi: 10.3788/IRLA201948.0405006
A high power Tm:YAP laser device was reported. The laser gain medium was b-axis-cut YAP/Tm:YAP/YAP composite crystal rod. By using a LD module with a center wavelength of 795 nm for double-end pumping, when the temperature of the cooling water was set at 20℃, and the total pump power was 301.4 W, the linear polarized laser output of 1.94 m with a maximum of 109.5 W was obtained. The optical-to-optical conversion efficiency was up to 36.3% and the slope efficiency was about 45.8%, the measured beam quality of M2 factor was 3.8 at the highest output power condition.
