Chunting Wu

Diode-pumped Q-switched Tm:LuAG ring laser operation at room temperature

Abstract2-μm lasers with high pulse energy and long pulse width of hundreds of nanoseconds are needed urgently in the accurate wind velocity lidar systems. This paper presented the acoustic-optical Q-switched Tm:LuAG laser performance in a pulsed-laser-diode end-pumping figure-eight ring resonator structure. Pulse energy and pulse width are investigated with the increasing of the incident pump energy at different repetition rate operation. Maximum energy of 3.3 mJ with the pulse width of 199 ns and 1.8 mJ with pulse width of 293 ns are obtained at the repetition rate of 20 and 50 Hz, respectively. Under Q-switched operation, the peak output wavelength is 2.022 μm at all time, and the beam quality factors are lower than 2 times diffraction-limited measured by a knife-edge traveling method.

Analysis of thermal effects in a pulsed laser diode end pumped single-ended composite Tm:YAG laser

By studying the theory of heat conduction, we established the transient heat conduction equation for a pulsed laser diode (LD) end pumped thulium doped laser. Combined with the actual working environment of a pulsed LD end pumped single-ended composite Tm:YAG rod, the expressions of transient temperature distribution and the time-varying thermal focal length were obtained by the integral transform method and the method of separation of variables. Under 240 mJ pump energy and repetition rates of 80, 90, and 100 Hz, thermal effects in the pulsed LD end pumped single-ended composite Tm:YAG rod were simulated, and the thermal lens focal length of the single-ended composite Tm:YAG rod was measured in experiments. The theoretical analysis was verified by the comparison between the theoretical results and the experimental results.

High-repetition-rate narrow pulse width mid-infrared optical parametric oscillator based on PPMgLN crystal

This paper reports a narrow pulse width optical parametric oscillator (OPO) based on periodically poled MgO:LiNbO3 (PPMgLN). When the maximum pumping power of the 1064?nm laser was 26.07?W, the acousto-optical (AO) Q-switch repetition rate was 70?kHz and the PPMgLN crystal grating period was 29 ?m; a 3840?nm mid-infrared light output power of 4.86?W was obtained at 150 ?C, corresponding to a pulse width of 9.56 ns. The optical?optical conversion efficiency was about 18.6%. In addition, by changing the temperature between 25 ?C to 200 ?C, a tunable mid-infrared wavelength of 3765?3974?nm output laser was achieved.

High-repetition-rate tunable mid-infrared optical parametric oscillator based on MgO: periodically poled lithium niobate

Abstract. A mid-infrared optical parametric oscillator (OPO) with an idler wavelength of 3.85 μm at a repetition rate of 200 kHz is presented, and a high-repetition-rate electro-optic (EO) Q-switched Nd∶GdVO4 laser with a double-crystal RbTiOPO4 EO modulator is used as the pump source. The OPO is designed as an extracavity singly resonant optical parametric oscillator. The threshold value of the OPO system is only 1.3 W at 1.06 μm. When the MgO: periodically poled lithium niobate (MgO: PPLN) crystal is operated at 90°C and the pump power is 10.5 W with a repetition of 200 kHz, a maximum average output power of 1.82 W at idler wavelength of 3.85 μm and pulse width of 14.3 ns are obtained. The slope efficiency of the 3.85-μm laser with respect to the pump laser is 21.3%. The M2 factors of the 3.85-μm laser are 1.84 and 1.76 in the parallel and perpendicular directions, respectively. The mid-infrared tunability of 3.7 to 3.9 μm can be achieved by adjusting the temperature of MgO∶PPLN crystal from 210 to 35°C.

Thermal effect in pulsed laser diode dual-end pumped Tm:YAG laser

Based on the actual working environment of pulse LD dual-end pumped Tm:YAG crystal, time-dependent temperature field analytical expression and the time-varying thermal focal length are deduced by the integral transform method. Additionally, the effects of pump power, repetition frequency and duty ratio on axial transient temperature distribution and time-varying thermal focal length of pulse LD dual-end pumped Tm:YAG rod are simulated and analyzed. The results show that the temperature distribution reaches steady state respectively by 11, 14, 15 pulses under pump power of 30W, 35W and 40W, respectively, while the frequency is 100Hz and the duty ratio is 50%. Under the condition mentioned above, the temperature of the crystal rod on both ends of the center arrives 34.7°C, 37.5°C, 40.3°C, which is 1.8°C, 2.1°C, 2.4°C higher than the center of rod. And the thermal focal length is in the range of 31.5-41.5cm, 26.5-34.6cm, 22.9-29.7cm, respectively. When pump energy is 100mJ, frequency at 110Hz, 120 Hz, 130Hz and duty ratio at 55%, 60%, 65%, respectively, the temperature distribution reaches steady state respectively by 13, 15, 16 pulses, and the temperature of the rod on both ends of the center respectively arrives 30.0°C, 30.9°C, 31.8°C, which is 1.3°C, 1.4°C, 1.5°C higher than the center of rod, and thermal focal length is in the range 46.4-58.8cm, 42.7-51.6cm, 39.5-45.9cm, respectively. Namely, as the increase of the pulses number, the distribution of the temperature and the thermal focal length in crystal rod appear jagged and eventually get to the periodic distributions. With the increase of the pump power, repetition frequency and duty ratio, the temperature difference between the crystal rod on both ends of the center and the center of rod is increasing, while time-varying thermal focal length gradually becomes shorter and the fluctuation range is smaller until it reaches steady state. The results provide theoretical basis for heating compensation and cavity design of pulsed thulium doped lasers.

Study on the laser crystal thermal compensation of LD end-pumped Nd:YAG 1319 nm/1338 nm dual-wavelength laser

The thermal model of laser diode (LD) end-pumped Nd: YAG was established. We analyzed the thermal effect of the crystal during the generation of 1319 nm/1338 nm dual-wavelength laser. Together with the bonded and non-bonded Nd:YAG crystal characteristics, we proposed to consider the bonded crystals internal temperature distribution of the three axes abc for the first time. The results showed that, compared with the non-bonded crystals, the bonded crystals could effectively reduce the crystal temperature. It provided a theoretical basis to solve the problem related to the thermal effect of the laser crystal and improve the laser output performance. The Nd:YAG laser crystal thermal model in this article could be widely applicable to similar laser crystals. The results provide a method to analyze and evaluate bonding crystal thermal compensation effectiveness by establishing the Nd:YAG crystals temperature distribution.

The influence of transmittances to the output characteristics of intra-cavity pumped self-Raman three-wavelength operation continuous wave laser

In this paper, the theoretical model of an intra-cavity pumped self-Raman continuous wave laser used to generate three-wavelength lasers simultaneous operation is propounded. In the model, the plane wave approximation and space-independent assumption are employed and the analytical expressions of the output power of three-wavelength lasers are derived. The influence of transmittances to the output characteristics are investigated by numerical simulation. In addition, the scheme of three-wavelength lasers simultaneous operation is proposed based on a theoretical model.

Widely tunable mid-infrared optical parametric oscillator based on a multiple periods MgO:PPLN

In this paper, we presented a widely tunable Mid-IR OPO based on a single multiple periods MgO:PPLN crystal, acousto-optical (AO) Q-switched Nd:YVO4 laser pumped by 880 nm laser diode (LD) was used as the pumping source. The OPO was designed as an extracavity single resonant optical parametric oscillator. When the grating period of the MgO:PPLN crystal was 31.5 μm and working temperature of 100°C, and the pump power was 10.95 W with repetition rate of 50 kHz, the single wavelength of 1.72 μm and idler wavelength of 2.78 μm was obtained respectively, the maximum average output power of the parametric lasers was 3.02 W, the pulse width of 7.9 ns was achieved. The optic-optic conversion efficiency was 27.58% from the 1064 nm pump laser to the parametric lasers. By tuning the grating period (28.5~31.5 μm) and the working temperature (25~192.1°C) of the MgO:PPLN, the single laser can be tuned from 1.46 μm to 1.72 μm, the corresponding idler laser can be tuned from 2.40 μm to 4.17 μm.

Room temperature operation of 2.67 mJ pulse LD end pumped Q-switched Tm:YAG laser

Due to 2 μm band in the absorption of water and CO2, the diode pumped solid state lasers with wavelength around 2 μm have important applications in laser medicine and remote sensing, such as it can be used as a scalpe or a light source of Coherent Doppler Wind Lidar and Differential Absorption Lidar. In the recently years, scientists have done much work on the development of such lasers. There’re many reports on continuous Tm:YAG laser. However, the study on Q-switched Tm:YAG laser, which is more useful in applications, was very rare. As the light source of Coherent Doppler Wind Lidar, large energy and wide pulse width is desired. Current reports mostly adopted CW pumped source, but it would make a mount of heat. Pulse pumping method could reduce the heat accumulation and improve the heat stability of the laser. How to improve the single pulse energy was the focus of current study. In this paper, a single end bonding Tm:YAG crystal with Tm3+ doping concentration of 3.5at.% was used. Acousto-optic (AO) Q-switched (GOOCH and HOUSEGO QS041-10M-HI8) operation was adopted in our experiment. In the repetition frequency of 100Hz, a maximum single energy of 2.67 mJ (measured by Ophir 30A-BB) and the narrowest pulse width of 149 ns (measured by Vigo PCI-3TE-12 detector) were achieved at room temperature. The M2x was 1.31 and the M2y was 1.35 (measured by Spiricon Pyrocam-III). Tm:YAG laser was developed by using a pulse diode pumped L shape resonant cavity. The transmittance of the curve output mirror was 4% and the curvature radius of which was 300 mm. The output center wavelength of the laser was measured to be 2013.5 nm (measured by YOKOGAWA AQ6375).

Analysis on the thermal effect of dual-end pumped Tm:YLF crystal

The theoretical model of thermal-steady-state anisotropic Tm:YLF crystal was built based on the practical operation condition. Integral transformation was used to get the analytical expression of the distribution of temperature in Tm crystal and thermal focal length. Matlab was used to simulate the influence of pump power density, crystal length and doping density to the distribution of temperature and thermal focal length. The results showed that under the invariant pumping power density and crystal length, the temperature rise and nonuniformity of thermal distortion are intensified by the increase of doping density which leads to a worse thermal effect. Under the invariant pumping power and doping density, the temperature rise and nonuniformity of thermal distortion are weaken by the modest increase of crystal length which leads to a good thermal condition. When the product of crystal length and doping concentration is a constant value, the thermal focal length keeps basic consistent. Furthermore, the simulated results are that when the dual-pumped power is 60W and waist radius is 430μm, the thermal focal length of 12mm, 3at.% doped which perpendicular and parallel to c axis are 184mm and 261mm respectively, and the thermal focal length of 12mm, 3.5at.% doped which perpendicular and parallel to c axis are 171mm and 243mm respectively. The results in this paper provide theoretical basis for thermal compensation and cavity design of dual-pumped Tm:YLF laser, meanwhile, the model built can be used to analyze other anisotropic crystals.