Advanced Solid-State Lasers: feature issue introduction.

This Joint Issue of Optics Express and Optical Materials Express features 40 peer-reviewed articles written by authors who participated in the Advanced Solid State Lasers Conference, part of the Optica Laser Congress and Exhibition held in Barcelona, Spain from December 11-15, 2022. This review provides a brief summary of these articles covering the latest developments in laser host and nonlinear crystals, structured materials, fiber lasers and amplifiers, ultrafast mode-locked lasers and optical parametric amplifiers, frequency-doubled Raman lasers, vortex beams, and novel concepts in laser design.

Narrow-linewidth operation of folded 1178nm VECSEL with twisted-mode cavity.

A vertical external-cavity surface-emitting laser (VECSEL) with a twisted-mode configuration is demonstrated. This architecture is particularly advantageous for power scaling of single-frequency VECSELs employing multiple gain mirrors in folded cavities. In such a configuration, some of the gain mirrors are inherently at the fold, and the lasing spectrum becomes unstable. This is caused by four waves interfering, destabilizing the standing wave pattern at the quantum wells. We show that the lasing spectrum can be narrowed by employing a twisted-mode configuration, which stabilizes the standing-wave pattern at the gain mirror. Furthermore, single-frequency output of more than 10 W at 1178 nm is demonstrated for a VECSEL employing two gain mirrors in a standing-wave cavity. In comparison, the output power for operation with one gain mirror only was 7.4 W when operating in single frequency. The choice of wavelength for the work reported in this paper is motivated by the opportunity to demonstrate compact VECSEL-based guide star lasers for adaptive optics via frequency doubling to the sodium D2 resonance at 589 nm.

A single shot coherent Ising machine based on a network of injection-locked multicore fiber lasers.

Combinatorial optimization problems over large and complex systems have many applications in social networks, image processing, artificial intelligence, computational biology and a variety of other areas. Finding the optimized solution for such problems in general are usually in non-deterministic polynomial time (NP)-hard complexity class. Some NP-hard problems can be easily mapped to minimizing an Ising energy function. Here, we present an analog all-optical implementation of a coherent Ising machine (CIM) based on a network of injection-locked multicore fiber (MCF) lasers. The Zeeman terms and the mutual couplings appearing in the Ising Hamiltonians are implemented using spatial light modulators (SLMs). As a proof-of-principle, we demonstrate the use of optics to solve several Ising Hamiltonians for up to thirteen nodes. Overall, the average accuracy of the CIM to find the ground state energy was ~90% for 120 trials. The fundamental bottlenecks for the scalability and programmability of the presented CIM are discussed as well.

Scalable approach for continuous-wave deep-ultraviolet laser at 213nm.

We present a novel approach for generation at 213nm in continuous-wave, corresponding to the fifth harmonic of common 1064nm laser, in pure continuous-wave mode. The approach is scalable in output power. Starting from two infrared fiber laser sources, we demonstrated 0.456W output at 213nm.

Single-frequency blue laser fiber amplifier.

An all-fiber amplifier for a single-frequency blue laser was demonstrated for the first time, to the best of our knowledge. Over 150 mW continuous-wave single-transverse-mode blue laser output was obtained with a 10 m 1000 ppm thulium-doped fluoride fiber pumped by a 1125 nm fiber laser at a power of 2 W. The output power was limited due to the onset of the competitive lasing at 783 nm. Photodarkening and photo-curing of the thulium-doped fiber amplifier were also studied and analyzed.

Continuous-wave, single-frequency 229 nm laser source for laser cooling of cadmium atoms.

Continuous-wave output at 229 nm for the application of laser cooling of Cd atoms was generated by the fourth harmonic using two successive second-harmonic generation stages. Employing a single-frequency optically pumped semiconductor laser as a fundamental source, 0.56 W of output at 229 nm was observed with a 10-mm long, Brewster-cut BBO crystal in an external cavity with 1.62 W of 458 nm input. Conversion efficiency from 458 nm to 229 nm was more than 34%. By applying a tapered amplifier (TA) as a fundamental source, we demonstrated magneto-optical trapping of all stable Cd isotopes including isotopes Cd111 and Cd113, which are applicable to optical lattice clocks.

Continuous-wave 193.4 nm laser with 120 mW output power.

This Letter describes an all-solid-state continuous-wave, deep-ultraviolet coherent source that generates more than 100 mW of output power at 193.4 nm. The source is based on nonlinear frequency conversion of three single-frequency infrared fiber laser master-oscillator power-amplifier (MOPA) light sources.

Injection-locked operation of an optically pumped semiconductor laser.

We demonstrate a single-frequency, continuous-wave, optically pumped semiconductor laser (OPSL) using an injection-locking technique. Parameters such as output coupling, injection power, and injection wavelength are investigated. With the proper parameters, the output power of the injection-locked laser exceeds the output power of its free-running condition. With 1.5 W of injection power from the master laser, over 9 W of output power is achieved at 1015 nm.

Doppler-free spectroscopy of mercury at 253.7 nm using a high-power, frequency-quadrupled, optically pumped external-cavity semiconductor laser.

We have developed a stable, high-power, single-frequency optically pumped external-cavity semiconductor laser system and generate up to 125 mW of power at 253.7 nm using successive frequency doubling stages. We demonstrate precision scanning and control of the laser frequency in the UV to be used for cooling and trapping of mercury atoms. With active frequency stabilization, a linewidth of <60 kHz is measured in the IR. Doppler-free spectroscopy and stabilization to the 6(1)S(0)-6(3)P(1) mercury transition at 253.7 nm is demonstrated. To our knowledge, this is the first demonstration of Doppler-free spectroscopy in the deep UV based on a frequency-quadrupled, high-power (>1 W) optically pumped semiconductor laser system. The results demonstrate the utility of these devices for precision spectroscopy at deep-UV wavelengths.

Continuous-wave single-frequency 295 nm laser source by a frequency-quadrupled optically pumped semiconductor laser.

Up to 136 mW of cw single-frequency output at 295 nm was obtained from a frequency-quadrupled optically pumped semiconductor laser. The highly strained InGaAs quantum-well semiconductor laser operates at 1178 nm in a single frequency. The single-frequency intracavity-doubled 589 nm output is further converted to 295 nm in an external resonator using beta-BaB(2)O(4).

Deep UV light generation by a fiber/bulk hybrid amplifier at 199 nm.

A high-pulse-repetition-frequency (PRF) pulsed light source in the deep ultraviolet region has been realized by a multiple wavelength conversion technique using a hybrid fiber/bulk amplifier system. Output of 199 nm with a power of 50 mW was achieved at 2.4 MHz PRF. The 1 microm amplifier consisted of a Yb-doped fiber amplifier and a Nd-doped YVO(4) amplifier. A 1.5 microm fiber master-oscillator power amplifier was employed as the other fundamental source. The amplifiers exhibited good amplification properties in pulse energy, polarization extinction ratio, and spectrum for nonlinear wavelength conversion.

Continuous-wave all-solid-state 244 nm deep-ultraviolet laser source by fourth-harmonic generation of an optically pumped semiconductor laser using CsLiB6O10 in an external resonator.

We report an all-solid-state laser system that generates over 200 mW cw at 244 nm. An optically pumped semiconductor laser is internally frequency doubled to 488 nm. The 488 nm output is coupled to an external resonator, where it is converted to 244 nm using a CsLiB(6)O(10) (CLBO) crystal. The output power is limited by the available power at 488 nm, and no noticeable degradation in output power was observed over a period of several hours.

Improved efficiency of a pulsed optical parametric oscillator by delayed double-pass pump.

By delaying the second pass of the pump of a singly resonant optical parametric oscillator, the conversion efficiency can be improved. We show the experimental results of an intracavity-doubled singly resonant parametric oscillator pumped by a Q-switched laser. Using 0.49 mJ of pump energy at 532 nm from a diode-pumped Nd:YAG laser, 0.085 mJ of 488 nm was obtained with the optimum delay for the second pass of the pump, giving a conversion efficiency of 17%. The improvement over the case of a single-pass pump was 85%, and the improvement over the double-pass pump with a small delay was 40%.