Electro-optic Q-switched Laser Research Articles

Electro-optical Q-switched laser array with one lamp pumping six Nd:YAG rods for programmable laser reconstruction in space-power-time domains

We report a novel laser array with one lamp pumping six Nd:YAG rods for programmable laser reconstruction in space-power-time domains. A sextuple ellipse pump cavity is proposed, and this scheme permits one xenon flash lamp with advantageously cylindrical pumping characteristics to simultaneously efficiently pump multiple Nd:YAG lasers in a laser system. The experimental setup was designed, and further experiments were carried out. The laser array can stably operate at a pumping rate of 1 Hz-10 Hz. Each laser beam of the six laser outputs has a divergence angle of less than 1.7 mrad, an output pulse of greater than 208 mJ, and a pulse width of approximately 10 ns, corresponding to a pulse peak power of approximately 20 MW. The laser array has a total output energy of 1.53 J at an electrical input of 93.3 J, corresponding to an overall electro-optical conversion efficiency of 1.64 % and an electro-optical slope efficiency of 3.17 %. Finally, laser array output pulses coded modulation in the space-power-time domains are achieved by electro-optical Q-switching. Therefore, the laser array provides the capability for programmable laser reconstruction in the space-power-time domains in a laser system for multipurpose applications, such as energy-tailored material processing, coded pulse laser ranging for improved signal-to-noise ratio (SNR), active optical remote sensing and scientific research.

Compact and highly stable electro-optic Q-switched laser at 1064 nm based on a composite YAG/Nd:YAG crystal

We report a compact and highly stable 1064-nm electro-optic Q-switched laser operating at the repetition rate of 1 kHz. A composite Nd:YAG crystal was used as the gain media and the cavity length was 105 mm. Under the average pump power of 11 W, the output power achieved 2.404 W with the pulse width of 4.558 ns, corresponding to the maximum peak power of 0.527 MW and the optical-to-optical conversion efficiency of 21.85%. The slope efficiency reached 42.69%. The beam quality in the horizontal (Mx2) and vertical (My2) directions were 1.81 and 1.58, respectively. The pulse timing jitter was less than 1 ns, and the average power fluctuation measured within 30 min was 0.83% (RMS). It is believed that such a compact and highly stable pulsed laser with high repetition rate, high peak power, and good beam quality has great potential in the fields of lidar, etc.

Dual-wavelength single-longitudinal-mode sub-ns lasers with high pulse repetition frequency

A theoretical model suitable to the dual-wavelength electro-optical Q-switched laser was established. Based on the optimizations on the time-varying Q-switched loss, doped concentration of the gain medium, and transmission of the output coupler, 1 kHz 1064 nm and 532 nm single-longitudinal-mode pulse lasers both with sub-nanosecond pulse width (PW) were obtained. The measured PWs of the dual-wavelength lasers agreed well with the theoretical predictions. At a pump energy of 3.7 mJ, the PWs of the 1064 nm and 532 nm lasers were 0.97 ns and 0.61 ns, the single pulse energy of the two lasers were 0.55 mJ and 0.29 mJ. The beam quality factor, the energy fluctuation and the time jitter of the 1064 nm laser were 1.58, 0.000063% and 2.18 ps; and that of the 532 nm laser were 1.35, 0.000011% and 1.56 ps.

High-Efficiency LD Corner-Side-Pumped Nd∶YAG Electro-Optical Q-Switched Laser

High-Efficiency LD Corner-Side-Pumped Nd∶YAG Electro-Optical Q-Switched Laser

Research on optimum slowly-rising driver for electro-optic Q-switched laser

Electro-optic Q-switch drivers that based on pulse transformer method have been widely used in laser engineering because of the advantages of concise circuits, low supply voltage, low lost, etc., but the long rise time and short pulse duration of the high voltage (HV) pulses have a considerable effect on the Q-switched laser outputs. In this paper, we experimentally investigated the dependence of Q-switched laser outputs on the rise rate of slowly-rising HV pulses in a flash pumped Nd:YAG laser with variable cavity lengths. LiNbO3 Q-switches with various dimensions were used. Based on the experiment results, the optimum slowly-rising HV pulses for any EO Q-switched laser were derived, the only requirement is that voltage near dynamic quarter-wave voltage during the emission of laser pulses. Additionally, the optimum outputs were found to be consistent with the results obtained by using a rapid-switching driver with a rise time of 7 ns. The optimum range of applied voltage was determined to be 0.88–1.12 times dynamic quarter-wave voltage.

Langasite electro-optic Q-switched [formula omitted] laser with high repetition rates and reduced driven voltages

Mid-infrared electro-optic Q-switched lasers with high repetition rates have many vital applications. However, the required voltage of electro-optic Q-switching is proportional to the wavelength leading to the severe piezoelectric ring effect, which limits its developments especially with high repetition rates. Based on the rate equation, this work designs a Langasite (LGS) electro-optic Q-switched laser with high repetition rates at 2μm by balancing the gain and loss in the cavity. The driven voltage determines the rotation of the polarization corresponding the loss in the cavity, and the gain depends on the incident pump power and repetition rate. By theoretical calculation, the driven voltage used in the high repetition rates is reduced to be 3.9 kV, which is 45% lower than the quarter-wave voltage. We demonstrated the LGS electro-optic Q-switched 2μm laser with a repetition rate of 200 kHz and pulse width of 5.52 ns. To the best of our knowledge, this work presents the highest repetition rate in the electric–optic Q-switched laser at 2μm and should be helpful for the design of Q-switched lasers with high repetition rates.

LD pumped folded electro-optic Q-switched laser

LD pumped folded electro-optic Q-switched laser

Progress on electro-optic crystals for Q-switches

Electro-optic Q-switched laser systems with high peak power have been widely applied in medical, cosmetology, measurement, processing, military industry, and other fields, while the crystal for electro-optic Q-switch is the core optoelectronic material for outputting high peak power pulse laser. With the technological progress and the development of short pulse, high repeat frequency and high power laser system application, the performance of crystals for electro-optic Q-switch is constantly improved. The paper reviews the research progress on basic characteristics, crystal preparation technology and electro-optic Q-switch application technology of several important electro-optic crystals for Q-switches including lithium niobate (LN) crystal, deuterated potassium dihydrogen phosphate (DKDP) crystal, low temperature phase barium metaborate (BBO) crystal, rubidium oxygen titanium phosphate (RTP) crystal, langasite (LGS) crystal and potassium titanium oxide phosphate (KTP) crystal, and propose that the research on practical electro-optic crystals for Q-switches is urgent to make breakthroughs. For a long time to come, exploring the electro-optic crystal materials, with high electro-optic coefficient, high laser damage threshold, stable performance, high temperature applicability and low cost, will be still an important issue in the field of crystal materials research.

Intrinsic reduction the depolarization loss in electro-optical Q-switched laser using a rectangular KD*P crystal

We presented the first demonstration of a new structure KD*P crystal as electro-optic switch, in which the thermal depolarization loss was intrinsically reduced. The thermally induced birefringence and depolarization of both cylindrical and rectangular crystalline structure were simulated. The higher pulse energy or average power output was achieved in the diode pumped E-O Q-switched laser using a rectangular KD*P crystal. At the repetition rate of 100Hz, the maximum average output power was 27.2W at 145A pump current, corresponding to the pulse energy was 272mJ with pulse width of 65ns and the beam quality of M2=20.4. Comparing the highest average power or corresponding single pulse energy, the laser with the rectangular KD*P crystal was two times of the laser with the traditional cylindrical KD*P crystal.

Efficient high repetition rate electro-optic Q-switched laser with an optically active langasite crystal.

With an optically active langasite (LGS) crystal as the electro-optic Q-switch, we demonstrate an efficient Q-switched laser with a repetition rate of 200 kHz. Based on the theoretical analysis of the interaction between optical activity and electro-optic property, the optical activity of the crystal has no influence on the birefringence during Q-switching if the quarter wave plate used was rotated to align with the polarization direction. With a Nd:LuVO4 crystal possessing a large emission cross-section and a short fluorescence lifetime as the gain medium, a stable LGS Q-switched laser was designed with average output power of 4.39 W, corresponding to a slope efficiency of 29.4% and with a minimum pulse width of 5.1 ns. This work represents the highest repetition rate achieved so far in a LGS Q-switched laser and it can provide a practical Q-switched laser with a tunable high repetition rates for many applications, such as materials processing, laser ranging, medicine, military applications, biomacromolecule materials, remote sensing, etc.

Dual-polarization electro-optical Q-switched ceramic laser

A dual-polarization electro-optical Q-switched Nd:YAG ceramic laser was studied. By selecting the appropriate size of calcite crystals, the dual-polarization Q-switched pulse was achieved by characteristics of calcite crystal. Experimental results show that compared with the traditional single-polarization electro-optical Q-switched laser, insertion loss is reduced, dynamic to static ratio is greatly improved, thermally induced birefringence of electro-optical Q-switched Nd:YAG ceramic laser is effective compensated. The output power of 19W and the pulse width of 13ns are obtained at the repetition rate of 1kHz and pumped power of 144W. The dynamic to static ratio is 71%. The results formed the basis for the further development of the high power and high efficiency ceramic red laser.

A 200 kHz Q-Switched Adhesive-Free Bond Composite Nd:YVO4 Laser using a Double-Crystal RTP Electro-optic Modulator

A diode-end-pumped electro-optic (EO) Q-switched adhesive-free bond composite Nd:YVO4 laser operating at a repetition rate of 200 kHz is reported. A pair of RbTiOPO4 (RTP) crystals are used as a high repetition EO Q-switch. At the repetition rate of 200 kHz, the maximum average output power of 11.8 W at wavelength 1064 nm and full width at half maximum of pulses of 16.65 ns are achieved at an incident pump power of 27 W, corresponding to an optical conversion efficiency of 43.7% and a slope efficiency of 44.6%, respectively. To the best of our knowledge, this is the highest repetition rate reported on the EO Q-switched laser by using RTP crystals.

Cholesteric Liquid Crystal Mirrors for Pulsed Solid-State Lasers

Abstract Cholesteric liquid crystals have been investigated as mirrors in an optical resonator for pulsed solid-state lasers. The out coupling efficiency has been optimized by tuning the reflectivity of the Cholesteric mirror with temperature. Furthermore, the polarizing properties of the helical Bragg-reflection have been used in an electro-optical Q-switched laser instead of the conventionally used combination of dielectric mirror plus polarizer. Pulses of 10 ns duration with peak intensities up to 1 GW/cm2 have been obtained. It is further shown that light-induced changes in reflectivity lead to a passive cavity-dumping and improved transverse beam profile, which may be also of interest for other photonics applications.