Two-dimensional Laser Diode Arrays Research Articles

Generation of one-dimensional high-order Hermite-Gaussian laser beams with large mode volume

Hermite-Gaussian (HG) beams have many important applications in the optical frontier, and the limited output power of the high-purity HG beams is partly due to the small gain volume of the mode. The commonly used off-axis end-pumped scheme offers a narrow gain volume whose diameter is about a hundred microns. In this work, a new method of generating the HG beams based on a slab resonator that has a large mode volume is proposed and experimentally demonstrated. According to the optical resonator theory, the intra-cavity modes in thickness and width direction of the slab resonator are restricted by inserting two size-adjustable apertures, respectively. The one-dimensional HG beam generation is mainly guaranteed by the size of the aperture along the thickness direction of the slab, which matches the diameter of the fundamental mode. The different order one-dimensional HG beams are obtained by refined intra-cavity mode modulation. Since the higher-order modes are less sensitive to the misalignment of the cavity mirror than the lower-order modes, and the manipulation of the modes-loss at different orders is achieved by combining the tilt control of the coupled output mirror and the size control of intra-cavity apertures. By adjusting the optical gain and loss in the resonant cavity, the single mode wins the competition of laser modes. Therefore, high-purity one-dimensional HG beams with 0 to 9 orders (HG<sub>00</sub> to HG<sub>09</sub>) are generated. The pump module is comprised of a two-dimensional laser diode array which offers face-pumping to the large surface of the slab, therefore the width of the mode volume is extended to several millimeters. By further incorporating the 100mm-level long slab, the total gain volume is much larger than the counterpart in the off-axis pumping scheme. In this work, the output power of the highest order HG<sub>09</sub> mode increases up to 244 mW. Owing to the large gain volume and uniform gain distribution caused by the face-pumped slab, the purity of high order HG modes is quite good. The correlation coefficient <inline-formula><tex-math id="M3">\begin{document}$ \rho $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M3.png"/></alternatives></inline-formula> between the measured intensity distribution and the theoretical value is larger than 0.95. The beam quality factor <inline-formula><tex-math id="M4">\begin{document}$ {M}^{2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M4.png"/></alternatives></inline-formula> is also in good agreement with the theoretical one. Finally, a conversion from Hermite-Gaussian beams to the donut-shaped Laguerre-Gaussian beams is realized by using an astigmatic mode converter. Hopefully, power scaling of the HG beam output is also expected by employing cascaded slab amplifiers, and the approach in this paper provides a novel solution for generation of high power HG beams.

Simulation of a two-dimensional laser diode array directly cooled by coolant flow

We report an analysis of attained output powers of laser diode bars (LDBs) and power densities of two-dimensional laser diode arrays (LDAs). A new LDA design is proposed and its thermal regime is simulated. The cw output power of the proposed LDA consisting of standard cw LDBs (output power 100 W, efficiency 50%, cavity length 2 mm) can reach 5 kW cm−2. The parameters of a coolant flow in the microchannels of the LDA heat sink necessary to achieve such powers are calculated.

Modelling of the thermal parameters of high-power linear laser-diode arrays. Two-dimensional transient model

A two-dimensional transient thermal model of an injection laser is developed. This model makes it possible to analyse the temperature profiles in pulsed and cw stripe lasers with an arbitrary width of the stripe contact, and also in linear laser-diode arrays. This can be done for any durations and repetition rates of the pump pulses. The model can also be applied to two-dimensional laser-diode arrays operating quasicontinuously. An analysis is reported of the influence of various structural parameters of a diode array on the thermal regime of a single laser. The temperature distributions along the cavity axis are investigated for different variants of mounting a crystal on a heat sink. It is found that the temperature drop along the cavity length in cw and quasi-cw laser diodes may exceed 20%.

Ultimate output parameters of laser-diode bars and arrays

An analysis was made of the influence of the series resistance of the heterostructure, of the threshold current density, and of the external differential quantum efficiency on the maximum efficiency of laser linear arrays (bars). It was found that the maximum efficiency can reach 75%. A heat sink design is suggested for ensuring that the ultimate output power is limited only by catastrophic optical damage to the cavity mirrors. The estimated ultimate output power density obtainable from a two-dimensional laser-diode array is 10 kW cm-2.

Two-dimensional Er:YSGG microlaser array pumped with a monolithic two-dimensional laser diode array

We have demonstrated one- and two-dimensional Er:YSGG microlaser arrays at 2.8-microm output wavelength with power levels up to 900 mW cw. The one-dimensional microlaser arrays are based on conventional edge-emitting laser diodes, and the two-dimensional microlaser arrays are based on surface-emitting monolithic two-dimensional laser diode arrays with 45-deg deflectors.

High-duty cycle, high-power two-dimensional laser diode arrays

Two-dimensional (2-D) laser diode arrays, stacked in a one square centimetre (1 × 1 cm2) format with five bars and five thick heat spreaders, achieve electrical-to-optical conversion efficiencies up to 44%. They have been operated at duty cycles up to 50% with up to 150 W of average power (300 W peak power).

A Simple Method for Measurement of Wavelength Chirping of a High-Peak-Power Laser Diode Array during Pulsed Operation

The wavelength chirping of a two-dimensional high-power laser diode array was measured by a newly developed method utilizing an absorption band of Nd:Y3Al5O12 (Nd:YAG). The validity of this method was verified by the time-resolved spectroscopic measurement. It was shown that this method is useful for the quantitative evaluation of the wavelength chirping and other emitting properties of a two-dimensional laser diode array.

High-power, continuous-wave, Nd:YAG microchip laser array

A transversely extended, flat-flat monolithic Nd:YAG laser cavity was pumped by a two-dimensional laser-diode array to form an array of cw microchip laser emitters with total output power of 9.8 W for an incident pump power of 38.5 W. The ensemble optical efficiency was 25.5%, the slope efficiency was 32.5%, and the beams were shown to have excellent spatial mode quality and parallelism.

Laser-diode-pumped transient mode locking

The authors have developed a pulsed diode-pumped mode-locked Q-switched and cavity-dumped Nd:YAG oscillator. Transient mode locking is discussed, with emphasis on the advantages of laser diode arrays as the pump source. Pulsed two-dimensional laser diode arrays are used to side pump the oscillator producing a single output pulse at 20 Hz with a pulse length of 95 ps and energy of 1 mJ.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Terrestrial and Extraterrestrial Superresonators as Drivers for an Inertial Confinement Fusion Reactor

The recirculating power fraction of a laser-driven inertial confinement fusion (ICF) reactor can be reduced by using laser diodes to pump a neodymium solid-state laser. To overcome the high costs of two-dimensional arrays of laser diodes, two types of superresonators are proposed: a terrestrially based one and an extraterrestrially based one on a geostationary orbit. Both are designed in such a way that a sequence of short laser pulses (10 to 20 ns wide), each with an energy of 5 to 10 MJ and a frequency of 10 Hz, are produced to trigger a deuterium-tritium ICF reactor. The terrestrial superresonator needs a much smaller number of two-dimensional laser diode arrays than a conventionally pumped “once-through” solid-state laser system, and the extraterrestrial resonator is pumped by means of concentrated solar radiation. In practice, at least an order of magnitude fewer laser diodes and crystalline calcium fluoride gain media are needed to meet the requirements of a laser driver for an ICF reactor. If, finally, a liquid neodymium laser system could be used for an ICF reactor, the cooling of the gain slabs would be facilitated substantially.

High power, high-efficiency quasi-CW two-dimensional laser diode arrays

Optical output power densities of 2000 W/cm2 have been obtained from 0.4 cm2 and 0.2 cm2 stacked AlGaAs laser arrays with electrical-to-optical conversion efficiencies of 43% for pulse widths of 200 μs. Arrays were assembled to facilitate back-cooling, and a five-bar stack was operated at 8% duty cycle with an average output power of 24 W.