Yongji Yu

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.

Q-switched Nd:YAG laser alternate symmetric side pumped by diode arrays

The laser diode side-pumped electro-optical Q-switced Nd:YAG laser of high single pulse output energy were studied. Two alternated semicircular LDA module was used to directly side pump the Nd:YAG crystal of a series of two-rod. Each module consists of 30 laser diode which peak power is 100W. KD*P crystals is used as the electro-optic Q switch. And the ABCD law of the Gaussian beam propagation is applied to calculate the area of the stability of the resonator cavity, and a more reasonable parameters of the resonant cavity is given. A 1064nm dynamics laser that maximum output energy of 140mJ and pulse width of 10ns is obtained at a repetition rate of 20Hz when the pump energy is 1200mJ.The optical-optical conversion efficiency is 11.7%.

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.

High repetition-rate and short pulse-width 1064nm laser in a composite crystal device

Compared with lamp pumped solid state laser, laser-diode pumped all-solid-state laser (DPSL) has the characteristic of high efficiency, long life and reliable under the condition of high repetition rate. Therefore, A high repetition rate DPSL has a broad application prospect in the laser detection, laser communication and optoelectronic countermeasure and other fields. Laser-diode (LD) pumped acousto-optic(AO) Q-switch all-solid-state has attractive features, such as compact structure, reliable operation, high repetition rate and short pulse width. Laser crystal is the core component of the laser. Usually composite crystal thermal lens focal length is three times more than traditional crystal, so it can avoid the serious heating effect of the operation material bumping by the traditional method. In this paper, we present a high repetition rate acousto-optic Q-switched Nd:YVO4 laser pumped by 880nm laser diode. By using the 0.25% doping concentration Nd:YVO4 single end composite crystal size of 3*3*(4+16) mm3 , with the 50 W LD pumped power, in order to calculate the laser crystal absorption efficiency of pump light, so that more accurate calculation of light conversion efficiency, first we measured 880 nm pump light absorption, crystal is calculated on the pump light absorption efficiency of 75%; When we put in the cavity mirror to form a flat resonant cavity, we obtained the 1064 nm continuous laser output power of 26 W and 27.1 W, with the output mirror transmittance of 20% and 48%, respectively. 50.7% and 48.7% optical to optical conversion efficiency has been achieved experimentally. When we put in AO Q-switch, with the repetition rate of 50 kHz, 100 kHz and 200 kHz, the 1064 nm laser output power is 21 W, 21.28 W and 20.58 W, and the peak power is 32.9 kW, 17.3 kW, 8.5 kW, respectively. Under the high repetition rate circumstance, the pulse width is limited to 12 ns.

Double-crystal RbTiOPO4 for simultaneous 200 kHz Q-switching and second-harmonic generation in a direct-pumped Nd:YVO4 laser

We report on electro-optic (EO) Q-switched intracavity second-harmonic generation (SHG) based on double-crystal RbTiOPO4 (RTP) in an 880 nm diode-end-pumped Nd:YVO4 laser for the first time. The double-crystal RTP performed simultaneously as a high repetition rate laser Q switch and a second-harmonic generator. At a repetition rate of 200 kHz, a maximum average output power of 2.51 W at 532 nm wavelength (, 1) and a shortest pulse width of 15.7 ns were achieved under an absorbed pump power of 21 W, corresponding to an optical–optical conversion efficiency of 11.9% and a slope efficiency of 12.8%, respectively.

LD dual-end-pumped CW Tm:YLF laser

We report on a LD dual-end-pumped 792nm continuous wave operation Tm:YLF laser. Firstly, the rate equation of LD end-pumped CW operation Tm:YLF laser were established, in which the energy transfer upconversion and without energy transfer upconversion under continuous-wave considerate were considered, as well the pump threshold and the slope efficiency of the laser system were analyzed. Simultaneously, the cavity stability condition and the pattern matching of the plano- concave resonator were analyzed according to ABCD Matrix theory. Comparing respectively the laser threshold and the slope efficiency and optical-optical conversion efficiency under circumstances which the output mirror transmittance of 15% and 23%. In addition, the M2 of the output laser were contrasted and analyzed in adjusting the resonator cavity length by using different radius of curvature of the output mirror in 150mm, 200mm and 300mm all in the above case. As the process of thermal lens focal length changing greater than 90mm, it exhibited that the two fundamental modes in the cavity resonator matched well in numerical simulation when the radius of curvature of the output mirror was 300mm, as well the two fundamental modes matched well when it more than 100mm in a certain pump power. We designed a single LD dual-end-pumped continuous wave operation Tm:YLF laser. Using Tm:YLF (3 at.%) crystal for gain medium, which the size was 3×3×14mm3. In experiments, the Tm:YLF laser crystal keeps 291K and the temperature control method is water cooling. The length of the resonator was 135mm when L shape plano-concave resonator was applied, and the radius of curvature output mirror was 300mm, as well as the temperature of the Tm:YLF laser crystal was 291K. The output laser we observed by this system and the central laser wavelength was 1944nm. The threshold power was 8.11W and the highest output power reaches to 4.01W when the totally input pump power was 17W, and the optical conversion efficiency was 23.6%. The far-field divergence angle was 3.8mrad after calculation. Respectively. The experimental results are coinciding with the theory.