Laser Diode Stack Research Articles

Nonsequential modeling of laser diode stacks using Zemax: simulation, optimization, and experimental validation

Modeling a real laser diode stack based on Zemax ray tracing software that operates in a nonsequential mode is reported. The implementation of the model is presented together with the geometric and optical parameters to be adjusted to calibrate the model and to match the simulated intensity irradiance profiles with the experimental profiles. The calibration of the model is based on a near-field and a far-field measurement. The validation of the model has been accomplished by comparing the simulated and experimental transverse irradiance profiles at different positions along the caustic formed by a lens. Spot sizes and waist location are predicted with a maximum error below 6%.

An optimization method for fly’s eye integrator

By analyzing how aberrations affect the performance of a fly’s eye integrator, an efficient method to optimize the performance is put forward. A fly’s eye integrator to be used to homogenize the beam of laser diode stack is designed as an example. The optimization method achieves optimized homogeneous illumination by minimizing the aberrations that degrade the homogeneity and transmission efficiency. By this means, it is possible to substitute two spherical lenses for the Fourier lens, which is usually used in a conventional fly’s eye integrator. This helps to reduce the cost without degrading its performance.

Beam-shaping method for uniform illumination by superposition of tilted Gaussian beams

Efficient beam shaping with uniform illumination is required in laser active imaging and detecting systems. In this paper, a beam-shaping method by superposition of tilted fundamental-mode Gaussian beams to produce nearly uniform illumination is proposed. The analytical formula for the average intensity of propagating multitilted Gaussian beams (MTGBs) is derived and used to study the uniformity of the beam profile with Fourier analysis. It is found that the MTGB maintains its flat-topped shape as it propagates and its uniformity is controlled by the parameters of fundamental-mode beams and superposition. Numerical examples are given. The method is used to reconfigure the beams of a high-power laser diode stack to form a MTGB shape for illumination of a 9×11.6-deg angular field. The simulation results from ASAP software show a shaping efficiency of 75%, and the rms deviation of the irradiance distribution from a flat-top shape is approximately 8%.

Conductively Cooled 1 kW—QCW Diode Laser Stacks Enabling Simple Fiber Coupling

A new mini-bar design densely packed with 13 emitters in a 1.6 mm aperture has been developed. These mini-bars deliver >200 W output. With a very low divergence of 95% power enclosed in 25° they are suitable for fast axis collimation (FAC) lenses with large working distance. The mini-bars are mounted on compact CuW carriers, which are further integrated into a custom stack assembly where they are conductively cooled from both sides. This completely AuSn soldered stack consists of only coefficient of thermal expansion matched materials and was 100 times temperature cycled from -40°C to 85°C, without any change in the PUI characteristic, the spectrum and the far field. The beam propagation factor M 2 of a 12-layer stack is ?130 in the vertical direction (after FAC) and ?210 in the lateral direction. Thus, the stack can be coupled to a 1.2 mm multi-mode fiber (M 2 = 260) with a coupling efficiency of 90% using only low-cost lenses.

28W average power hydrocarbon-free rubidium diode pumped alkali laser

We present experimental results for a high-power diode pumped hydrocarbon-free rubidium laser with a scalable architecture. The laser consists of a liquid cooled, copper waveguide which serves to both guide the pump light and to provide a thermally conductive surface near the gain volume to remove heat. A laser diode stack, with a linewidth narrowed to approximately 0.35 nm with volume bragg gratings, is used to pump the cell. We have achieved 24W average power output using 4 atmospheres of naturally occurring helium ((4)He) as the buffer gas and 28W using 2.8 atmospheres of (3)He.

激光二极管阵列端面抽运混合腔Nd:YVO4板条1064 nm和1342 nm激光特性研究

激光二极管阵列端面抽运混合腔Nd:YVO₄板条1064 nm和1342 nm激光特性研究

High-repetition-rate Nd:YVO4 slab laser with a 1-D top-hat output beam

A high-repetition-rate electro-optic Q-switched Nd:YVO4 slab laser is demonstrated in this paper. The Nd:YVO4 slab inside the compact resonator is end-pumped by a 2-bar laser diode stack. The output beam with one dimension (1-D) top-hat intensity distribution at both near field and far field is generated. Continuous wave (CW) output of 13 5 W is obtained under the total pump power of 50 W. At the repetition rate of 40 kHz, the energy per pulse is 0.32 mJ with its pulse width of 26.3 ns. At 20 kHz, we have achieved the maximum pulse energy of 0.56 mJ and 56 kW peak power with 10 ns pulse width.

用有源区无铝的宽波导和分立铜微通道封装技术实现高密度激光二极管列阵

A high packing density laser diode stack array is developed utilizing Al-free active region laser bars with a broad waveguide and discrete copper microchannel-cooled heatsinks. The microchannel cooling technology leads to a 10-bar laser diode stack array having the thermal resistance of 0.199 oC/W, and enables the device to be operated under continuous-wave (CW) condition at an output power of 1200 W. The thickness of the discrete copper heatsink is only 1.5 mm, which results in a high packing density and a small bar pitch of 1.8 mm.

Preparation and characterization of transparent Nd:YAG ceramics

AbstractTransparent Nd:YAG ceramics were produced by solid.state reaction of high.purity (4N) nanometric oxides powders, i.e., Al2O3, Y2O3 and Nd2O3. After sintering, mean grain sizes of 2% Nd:YAG samples were about 20 μm and their transparency were a bit worse than that of 0.9% Nd:YAG single crystal. Two types of active elements: rods and slabs were fabricated and characterized in several diode pumping schemes. In end pumping configuration as a pump source 20.W fiber coupled laser diode operating in low duty cycle regime (1 ms pump duration/20 Hz) was deployed. In the best case, 3.7 W of output power for 18 W of absorbed pump power, M2 < 1.4 were demonstrated for uncoated ceramics Nd:YAG rod of ϕ 4×3mm size in preliminary experiments. For the ceramics of two times lower Nd dopant level above 30% slope efficiency was achieved. In case of Nd:YAG ceramic slab side pumped by 600.W laser diode stack above 12 W was demonstrated with slope efficiency of 3.5%.

High-power diode-pumped Tm:YLF slab laser

A 2% Tm3+-doped LiYF4(Tm:YLF) slab is double-end-pumped by two laser diode stacks. The pumped volume has a rectangular cross section. The Tm:YLF laser produced 148 W of continuos-wave output at 1912 nm in a beam with M x 2 ≈199 and M y 2 ≈1.7 for 554 W of incident pump power. The slope efficiency with respect to the incident pump power was 32.6%, and the optical-to-optical efficiency was 26.7%.

Transient wavelength performance of 153 μm InP laser diodes for pumping of Er^3+-doped solid-state lasers

The transient wavelength performance of high-power InP laser diode stacks with internal Bragg gratings is studied experimentally. Because of the wavelength selective nature of the internal grating, which is decoupled from the actual gain profile dynamics of the laser diode, the wavelength drift with respect to temperature and current is greatly reduced and steady-state conditions are reached after a short settling time of less than 50 ms.

Laser diode array pumped continuous wave Rubidium vapor laser

We have demonstrated continuous wave operation of a laser diode array pumped Rb laser with an output power of 8 Watts. A slope efficiency of 60% and a total optical efficiency of 45% were obtained with a pump power of 18 Watts. This laser can be scaled to higher powers by using multiple laser diode arrays or stacks of arrays.

High peak power Nd:YAG laser pumped by 600-W diode laser stack

The Q-switched laser with triangle slab made of Nd:YAG crystal side pumped by 600-W quasi-cw diode laser stack has been designed. The multimode ( M 2≈2.6) output energy of about 42 mJ was demonstrated in free running mode for110-mJ pump energy. In Q-switch experiments, the KDDP Pockels cell was placed between the slab and rear mirror in plane-plane cavity with output coupler of 84% transmission. The energy of 8 mJ in 2.1-ns pulse duration was obtained for near TEM 00 output beam. For passive Q-switching by means of Cr:YAG crystal of 12.6% unsaturated transmission, the energy of 5.1 mJ in 2.5-ns pulse duration was obtained for output beam close to TEM 00 mode.

Eliminating dead spaces of the laser diode stack in the fast-axis direction using a plane-parallel plate array

Dead spaces are generated in the fast-axis direction of the laser diode stack (LDS) because of the construction of the LDS. A new method of using a plane-parallel plate array to eliminate dead spaces between the bars of the LDS is presented. The design method of the plane-parallel plate is also investigated, and the beam parameter product is used to evaluate the quality of the beams. As an example, the plane-parallel plate array for an LDS consisting of four bars is designed and simulated. The simulation results show that the dead spaces are eliminated, the spots size is compressed from 6.5 mm×10 mm to 3.5 mm×10mm, and the energy loss is about 2%.

Thin Nd:YAG slab laser pumped by lens duct coupled diode laser stacks

High power continuous wave operation of a diode face-pumped thin Nd:YAG slab laser is reported. A novel pumping geometry for a thin Nd:YAG slab using cylindrical lens duct coupled diode laser stacks is demonstrated. In a close-coupled resonator, a maximum laser output power of 260 W in multimode operation is obtained. This corresponds to a slope efficiency of 34% and an optical-to-optical efficiency of 27%, respectively. In high-brightness operation, a polarized laser output of 70 W has been obtained with a beam quality factor close to 4 in both directions. The polarization contrast ratio is >100.

Passively <inline-formula><math altimg="none" display="inline" overflow="scroll"><mi>Q</mi></math></inline-formula>-switched neodymium slab lasers at <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mn>1.3</mn><mtext>-</mtext><mi>μ</mi><mi mathvariant="normal">m</mi></mrow></math></inline-formula> wavelength side-pumped by a <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mn>600</mn><mtext>-</mtext><mi mathvariant="normal">W</mi></mrow></math></inline-formula> laser diode stack

Triangular slabs made of Nd:YAG or Nd:YAP crystals were tested as active media for diode-pumped lasers. The resonator arrangements for the Q-switched regime were prepared for emission corresponding to the Nd3+ ion transition 4F3/24I13/2 in each crystal (=1318 nm for Nd:YAG, and =1342 nm for Nd:YAP). Optical pumping was accomplished by a fast-axis collimated quasi-cw diode laser stack with peak power of 600 W delivering up to 150 mJ of pump energy. In free-running regime, the maximum reached energies were 24 and 27.5 mJ for Nd:YAG and Nd:YAP crystals, respectively. The corresponding slope efficiencies were 19.9% and 23.7% for Nd:YAG and Nd:YAP laser oscillators, respectively. The passive Q switching for 1.3-µm wavelength was accomplished by means of a saturable absorber made of V3+:YAG crystal, whose initial transmission was optimized for the shortest possible pulse length. The 6-ns-duration giant pulses were obtained with energies of 740 and 432 µJ for Nd:YAG and Nd:YAP, respectively. These results correspond to attained peak powers of 125 kW (Nd:YAG) and 77 kW (Nd:YAP) in the fundamental TEM00 mode, which allows this laser to be used as an efficient source for further nonlinear conversion or other applications.

Beam-shaping technique for improving the beam quality of a high-power laser-diode stack

We report a beam-shaping technique that reconfigures the beams to improve the beam quality and enhance the power density for a ten-array high-power laser-diode stack by using two optical rectangular cubes and two stripe-mirror plates. The reshaped beam has threefold improvement in beam quality, and its power density is effectively enhanced. On the basis of this technique, we focus the beam of the high-power laser-diode stack to effectively end pump a high-power fiber laser.

Efficient, high-brightness wavelength-beam-combined commercial off-the-shelf diode stacks achieved by use of a wavelength-chirped volume Bragg grating

We report a method of scaling the spatial brightness from commercial off-the-shelf diode laser stacks through wavelength beam combining, by use of a linearly wavelength-chirped volume Bragg grating (VBG). Using a three-bar commercial stack of broad-area lasers and a VBG, we demonstrate 89.5 W cw of beam-combined output with a beam-combining efficiency of 75%. The output beam has a propagation factor M2 approximately 26 on the slow axis and M2 approximately 21 on the fast axis. This corresponds to a brightness of approximately 20 MW/cm2 sr. To our knowledge, this is the highest brightness broad-area diode laser system. We achieve 81% coupling efficiency into a 100 microm, 0.22 N.A. fiber.

High power collimated diode laser stack

A high power collimated diode laser stack is carried out based on fast-axis collimation and stack packaging techniques. The module includes ten typical continuous wave (cw) bars and the total output power can be up to 368W at 48. 6A. Using a cylindrical lens as the collimation elements, we can make the fast-axis divergence and the slow-axis divergence are 0.926 4° and 8.206° respectively. The light emitting area is limited in a square area of 18.3 mm×11 mm. The module has the advantage of high power density and offers a wide potential applications in pumping and material processing.

Effective Suppression of Beam Divergence for High-Power Laser-Diode Stack Based on External-Cavity Technique

We demonstrate an off-axis external-cavity configuration designed to effectively suppress the beam divergence of a high-power laser-diode stack. The off-axis external cavity consists of a set of beam-transformation systems and a stripe mirror. Thirty-eight off-axis external-cavity laser diodes are individually formed for the high-power laser-diode stack. At a drive current of 40 A, the divergence angle of the slow axis is reduced from 7.6° without the external cavity to 1.6° with the external cavity. The external-cavity laser-diode stack achieves a cw power output of 45 W, or 72.4% of the cw power output of a free-running laser-diode stack.