High-power Laser Diode Arrays Research Articles

Generation of tunable continuous-wave THz signals using high-power multiple wavelengths DFB diode laser array

We report a high-power multiple wavelengths distributed feedback (DFB) diode laser array chip for generating continuously tunable terahertz (THz) signals. Each laser within this laser array chip outputs a single-mode output power of up to 90 mW, with a maximum single-mode output power exceeding 120 mW, and the narrowest linewidth is 32.6 kHz. By employing optical heterodyne approach using a commercial uni-traveling-carrier photodiode (UTC-PD), we demonstrated a continuously room temperature tunable THz signal output spanning frequency range of 0.075 THz to 2.63 THz. Our high-power multiple-wavelengths DFB diode laser array chip has achieved a record continuously tunable range with high power and narrow linewidth, providing a high-power, low-cost, and compact photonic chip solution for room temperature continuously tunable terahertz sources.

Design and experiment of 10 kW-level laser with high-uniformity distribution and large-size output beam

A 11.5 kW laser irradiation source was established to study the pyrolysis and fire of combustibles. The high-power laser diode array (LDA) is first used in the laser irradiation source. By using the homogenized waveguide and large-aperture reshaper, we obtained the high-uniformity distribution and large-size beam simultaneously. The intensity uniformity and the beam size were 95 % and 102.3 mm respectively, correspondingly the power intensity was 1.4 MW/m2. To the best of our knowledge, this is the first time to realize the large-size high-uniformity and MW/m²-level laser irradiation source, which lays a solid foundation for the experiment of the pyrolysis and fire of combustibles induced by the light irradiation. In addition, by the innovative designs, it is effectively enhanced that the damage threshold and the thermal stability of homogenized waveguide under the high-power CW laser.

Tunable, High-Power, Narrow-Linewidth Diode Laser for Potassium Alkali Metal Vapor Laser Pumping

This work proposes a method of compressing spectral linewidth and tuning the central wavelength of multiple high-power diode laser arrays in an external cavity feedback structure based on one volume Bragg grating (VBG). Through the combination of beam collimation and spatial beam technologies, a diode laser source producing 102.1 W at an operating current of 40 A is achieved. This laser source has a central wavelength of 766 nm and a narrow spectral linewidth of 0.164 nm. Moreover, a tuning central wavelength ranging from 776–766.231 nm is realized by precisely controlling the temperature of the VBG, and the locked central wavelength as a function of temperature shifts at the rate of approximately 0.0076 nm/°C. The results further prove that the smile under 1 μm can restrain the self-excitation effect of the emitting laser, which can influence the efficiency of the potassium alkali metal vapor laser pumping.

Color quality consideration when switching from FL to LED

Color quality consideration when switching from FL to LED

Thermoelastic stresses in high-power CW diode laser arrays assembled on CuW and AlN submounts

Comparative results are presented of 3D-calculation for thermoelastic stress (TES) profiles in diode laser arrays (LDAs) assembled on CuW and AlN submounts (temperature compensators) and operating at a continuous-wave (CW) thermal power load of up to 220 W. For the first time, the simulation has revealed substantial differences in the maximal TES values for the arrays assembled on CuW and AlN submounts, as well as pronounced features of TES distribution in LDA assemblies, in particular, near the rear (highly reflecting) mirror of the laser diode cavity in similar geometries of temperature compensators. Results of the numerical simulation qualitatively agree with thorough measurements of spectral distributions over the LDA emitting aperture. The obtained results are interesting for mastering the production technologies of high-power devices aimed at improving their output parameters and service life.

Optimization of a microchannel heat sink using entropy minimization and genetic aggregation algorithm

A copper heat sink with rectangular U-shaped microchannels for cooling high power laser diode arrays was numerically optimised. The control volume method based commercial software was applied for solving heat transfer and fluid flow in the considered device. The optimisation procedure included over 130 various geometrical configurations with five independent geometric parameters. The Entropy Generation Minimization criterion was applied to find the optimal geometric structure. Some relations between geometrical parameters of the microchannel heat sink were analysed through statistical studies and two most important ones, i.e., the relative height (α) and width (β) of a single microchannel, were selected. Using the genetic aggregation, the entropy generation characteristics were determined as a function of α and β as well as mass flow rate of cooling medium (Ġ). The most optimal from the second law of thermodynamics point of view configuration was the one with αopt = 0.86, βopt = 0.347 and Ġ = 0.00183 kg/s. Comparing with the initial geometry, over 35% reduction of irreversibility losses for the optimal heat sink had been achieved, i.e., heat sink thermodynamic efficiency increases from 90.05% to 91.8%, while maximum temperature of cooled semiconductor element was reduced from 333.3 K to 324.2 K.

A Review On Transient Thermal Management of Electronic Devices

Abstract Much effort in the area of electronics thermal management has focused on developing cooling solutions that cater to steady-state operation. However, electronic devices are increasingly being used in applications involving time-varying workloads. These include microprocessors (particularly those used in portable devices), power electronic devices such as IGBTs, and high-power semiconductor laser diode arrays. Transient thermal management solutions become essential to ensure the performance and reliability of such devices. In this review, emerging transient thermal management requirements are identified, and cooling solutions reported in the literature for such applications are presented with a focus on time scales of thermal response. Transient cooling techniques employing actively controlled two-phase microchannel heat sinks, phase change materials (PCM), heat pipes/vapor chambers, combined PCM-heat pipes/vapor chambers, and flash boiling systems are examined in detail. They are compared in terms of their thermal response times to ascertain their suitability for the thermal management of pulsed workloads associated with microprocessor chips, IGBTs, and high-power laser diode arrays. Thermal design guidelines for the selection of appropriate package level thermal resistance and capacitance combinations are also recommended.

Testing Characterization and Simulating Optimization of High-power Laser Diode Array Chips

Testing Characterization and Simulating Optimization of High-power Laser Diode Array Chips

Photodetachment of negative ion beams for the ion-neutral merged-beam experiments at RICE

SynopsisGeneration of neutral atomic beam is under development for the ion-neutral merged-beam experiment at the RIKEN Cryogenic Electrostatic ion storage ring (RICE). The beam is produced by a photodetachment of a negative ion beam using a high power laser diode array with a wavelength of 808 nm. In order to increase the detachment efficiency, we have developed an optical cavity built with a planar mirror. In this presentation we will present the current status of the neutral atom beam source.

By-Emitter Analysis of 450-nm Emitting High-Power Diode Laser Bars

We present an analysis of optical and thermal properties of GaN-based blue-emitting high-power diode laser arrays (bars). Parameters such as emission power and temperature are monitored for each single emitter of arrays consisting of 23 emitters. The obtained data are compared with modeling of the electro-optic properties. In contrast to the well-known infrared bars, the thermal properties in the blue-emitting bars control the individual emitter properties to a very high degree and lead to considerable variations in emitter power, in extreme cases up to 50%. Such extreme cases occur, for example, when emitters fail and thus act as a heat source for their surroundings. Nevertheless these bars reach record output powers and are on the way to becoming major sources of photonic power in the blue spectral range.

Experimental study on cooling of high-power laser diode arrays using hybrid microchannel and slot jet array heat sink

In this study, a hybrid microchannel and slot jet array heat sink is designed and fabricated to achieve a better thermal performance of the high-power laser diode arrays. A standard commercial laser bar with wavelength of 808 nm is packaged on the heat sink and experiments are performed to assess the cooling performance of the hybrid heat sink. In the experiments, the forward voltage method is used to measure the chip temperature and the structure function method is applied to obtain the thermal resistance of the heat sink. Using the deionized water as coolant, the heat sink deals with a heat flux of up to 506 W/cm2 and the thermal resistance of the heat sink is only 0.23 K/W when the flow rate is 0.8 L/min (The average jet velocity is 13.3 m/s). The optical power can be up to 135.5 W corresponding to the wall plug efficiency of 64.2%. Compared with the published solutions related to cooling similar laser chips, the thermal resistance reduces by over 15%, indicating that this hybrid heat sink is an interesting solution to improve the cooling of the high-power laser diode arrays.

Vascularized liquid metal cooling for thermal management of kW high power laser diode array

In this paper, the vascularized liquid metal cooling was introduced into the thermal management of high power laser diode array (HPLDA) to realize an excellent heat removal performance. A vascularized liquid metal heat sink, with channel number of 70 and characteristic dimension of 1.8 mm, was firstly designed. And experimental tests and numerical analysis were then conducted. The experimental results indicated that liquid metal cooling can achieve 2000 W heat dissipation of HPLDA, with maximum temperature of heat sink top surface lower than 54 °C. The numerical results showed that vascularized liquid metal cooling offers better cooling performance compared to vascularized water cooling when flow rate was bigger than 2.4 l/min. It was also found that the heat capacity resistance was a significant thermal resistance for vascularized liquid metal cooling, while it was rather small for vascularized water cooling. Finally, the optimization distribution of heat source was numerically conducted to reduce the maximum temperature and maximum temperature difference, and 40 mm * 72 mm HPLDA distribution was selected as the best choice. Overall, the advanced vascularized liquid metal convection cooling offers a novel and effective heat dissipation method for the thermal management of HPLDA.

Numerical study on cooling of high-power laser diode arrays using slot jet array impingement

Thermal design shows significant effects on energy conversion efficiency, lifespan and beam quality of high-power laser diode arrays (HPLDAs). In this study, a slot jet array heat sink (SJAHS) is designed to improve the cooling performance of HPLDAs, and numerical simulations were conducted to optimize the flow and heat transfer in the heat sink. Flow passages inside the heat sink ensured that the coolant is allocated to every jet uniformly. The jet geometry is optimized to enhance the heat transfer. When the working fluid is assumed as water at 293 K inlet temperature and at a flowrate of 800 mL/min, the heat sink is capable of removing 150 W heat over an area of 15 mm2 with a maximum temperature increase of 52.75 K from the coolant inlet to emitters. It means that the emitter-to-coolant thermal resistance is 0.35 K/W without considering the interface thermal resistance. The corresponding pressure drop is 361 kPa. Compared with the existing microchannel heat sink, the numerical results implied that this new heat sink possesses a better cooling performance.

Three-dimensional thermal model of high-power semiconductor lasers.

In this paper, 3-D, steady-state, analytical thermal models of high-power single-emitter semiconductor lasers (SEs) and laser diode arrays (LDAs) are derived, considering the heat conduction in multi-layered laser structures. Heat flow in the laser chips for an epi-down bonded SE and LDA is described using this model, and it is observed that the laser chips contribute to 8% and 6% of total heat dissipation for the SE and LDA, respectively. The submount size requirement for this model is discussed by revealing the heat flow in the submount. Through finite element simulations, the solution accuracy for the lasers with non-ideal submounts is confirmed. Finally, the performance of our proposed analytical models is verified by finite element simulations and experimental measurements based on the wavelength shift method.

Second harmonic generation of ultraviolet laser based on high power laser diode array

A 780 nm continuous-wave, which is output by extra-cavity semiconductor laser with a bulk bragg grating, is used as the fundamental input light source of the Second Harmonic Generation (SHG) system. Line width of the fundamental light is 0.13 nm. Based on the type I phase-matching and Lithium Triborate (LBO) crystal, 390 nm second harmonic is obtained. The emitted average output power is 30 W (SHG efficiency is 0.01%). We provide a new technical route for the achievement of high-power UV beams.

Temperature distribution and thermal resistance analysis of high-power laser diode arrays

The accurate temperature measurement of high-power laser diode arrays is a considerable challenge due to their large temperature gradient and package structure. In this study, experiments based on the forward voltage method were set up to measure the transient temperature behavior of chips after the removal of heating load. A hybrid experimental/numerical method was developed to calculate multiple unknown interface thermal resistances and improve the prediction of the temperature distribution of high-power laser diode arrays by analyzing the transient temperature behavior of chips. The largest deviation between numerical and experimental results is 1.3 K. Based on the numerical results, thermal resistances for different layers and temperature distribution inside the chip were obtained and evaluated. Some suggestions for improving the thermal design of high-power laser diode arrays were derived.

Research on 200 mJ semiconductor end-pumped MOPA Laser

Using the high-power laser diode array (LDA) end-pumped Nd:YAG laser bar method, combined with the design of the convex-concave unstable cavity, the average energy of the small beam divergence laser output was achieved about 83 mJ under 20 Hz operating conditions. Then taking the laser as the oscillation source, the same method of the LDA end-pumped Nd:YAG laser rod was used for energy amplification to form an LDA end-pumped master oscillator-power amplification (MOPA) laser, which finally obtained the pulsed laser output with a repetitive frequency of 20 Hz, an average energy of >200 mJ, a divergence angle < 2.1 mrad and an energy fluctuation < ±2.5%. The laser has a optical-to-optical conversion efficiency of about 14.6%, a volume of 175×91×49 mm3, a mass of < 1 kg, and a divergence angle of < 0.3 mrad after transmitted through an 8× transmission antenna.

Design of Pulse Power Supply for High-Power Semiconductor Laser Diode Arrays

This paper mainly introduces a design circuit and control method of pulse power supply for high-power semiconductor laser diode arrays. According to the high voltage and large current operating characteristics of semiconductor laser, the control strategy of multi-module cascade topology combined with multiple MOSFET connected in parallel is adopted. The topology of multi-module cascade is presented to meet the requirement of wide output voltage range. The multiple MOSFET connected in parallel in the grounding module is proposed to increase output current of the pulse power supply, and each MOSFET has exclusive closed-loop regulator. The pulse current is controlled by the gate driving voltage of the MOSFET which operates in the linear zone, which can ensure the pulse current to be smooth and stable without overshoot. Digital control and analog control are combined to make the control of the pulse power supply more flexible. An experimental platform with a pulse power of 132.3 kW is built. The parameters of pulse power supply are exhibited: pulse current 210 A, pulse voltage 630 V, pulse width 200μs, and repetition frequency 100 Hz.

Low Etendue Yellow-Green Solid-State Light Generation by Laser-Pumped LuAG:Ce Ceramic

A low Etendue (6.1 mm2) yellow-green solid-state light source with optical conversion efficiency up to 101.3 lumen/Watt is demonstrated by through high-power laser diode pumping of a static LuAG:Ce transparent ceramic plate. A 443-nm blue laser diode array with a full-width-half-maximum (FWHM) of <1.5 nm and a maximum output power of 15.2 W is used to attain a high spectral absorption efficiency. The output from the high-power laser diode array is collimated, shaped, despeckled, and focused to display a Gaussian-like profile with a 1.5-mm beam waist (1/e2 radius) to stimulate a 1.2-mm thick LuAG:Ce transparent ceramic plate with an emission FWHM spectra at 505–585 nm. No thermal quenching, pump absorption saturation, and obvious luminous flux decrease is found during test.

Thermomechanical Behavior of Conduction-Cooled High-Power Diode Laser Arrays

Thermomechanical behavior has an important effect on reliability and lifetime of high-power diode lasers (HPDLs). Finite-element analysis (FEA) model and analytical solution model of the conduction-cooled package (CS) HPDL are established to analyze the thermomechanical behavior including normal stress, shearing stress, and displacement in reflowing process and working process. Moreover, in order to simulate and analyze the thermomechanical behavior in total process, reflowing thermal stress and displacement are considered as the residual stress and the initial condition of working process. We find that shearing stress is the origin of other thermomechanical behavior due to coefficient thermal expansion (CTE) mismatch, while both CTE mismatch and temperature gradient cause the thermal stress and displacement in working process. Although thermal stresses and displacement induced in reflowing process are larger than working process, the working process has great impact on smile and causes much worse total smile. The influence of different working temperatures on smile is also studied in total process with analytical solution, FEA, and experiment. For analytical solution, the total smile value is inversely proportional to the working temperature, while for FEA the smile value is proportional to the working temperature and FEA result accords with experimental result.