Frequency stabilization of an ultraviolet semiconductor disk laser

We report a tunable, narrow-linewidth UV laser based on intracavity second-harmonic generation in a red semiconductor disk laser. Single-frequency operation is demonstrated with a total UV output power of 26 mW. By servo-locking the fundamental frequency to a reference Fabry–Pérot cavity, the linewidth of the UV beam has been reduced to 16 kHz on short timescales and 50 kHz on a 1 s timescale, relative to the reference

Towards compact and portable sub-kHz AlGaInP semiconductor disk lasers for cold atom experiments

Stable lasers are crucial for experiments that target narrow atomic transitions (kHz down to Hz linewidth). Such transitions are used, for example, to cool and trap atoms in magneto-optical traps down to the μK regime, in particular for optical clock systems. In this context, semiconductor disk lasers (SDLs) have demonstrated great potential due to their spectral flexibility, high brightness, and low intensity and frequency noise. Here we report our recent progress in frequency stabilisation of an AlGaInP SDL designed for ultra-narrow linewidth at 689 nm for a strontium clock, achieving sub-kHz RMS frequency noise, relative to a reference Fabry-Perot resonator

Tunable narrow linewidth AlGaInP semiconductor disk laser for Sr atom cooling applications

We report a frequency stabilised semiconductor disk lasers based on AlGaInP and operating at 689 nm, a wavelength of interest for atomic clocks based on strontium atoms. With a gain structure designed for emission at around 690 nm, more than 100 mW of output power was generated in single frequency operation. We show that the source can be tuned over 8 nm with picometer precision. By servo-locking the frequency to the side of fringe of a reference cavity, we demonstrate rms frequency noise of 5.2 kHz

Characterization of single-crystal synthetic diamond for multi-watt continuous-wave Raman lasers

A continuous-wave diamond Raman laser is demonstrated with an output power of 5.1 W at 1217 nm. This Raman laser is intracavity pumped by a side-pumped Nd:YLF rod laser: a 43-fold brightness enhancement between the Nd:YLF and diamond Raman lasers is observed, with the M2 beam propagation factor of the diamond Raman laser measured to be <; 1.2. Although higher output powers are demonstrated in a similar configuration using KGd(WO4)2 (KGW) as the Raman laser material (6.1 W), the brightness enhancement is much lower (2.5 fold) due to the poorer beam quality of the KGW Raman laser (M2 <; 6). The Raman gain coefficient of single-crystal synthetic diamond at a pump wavelength of 1064-nm is also measured: a maximum value of 21±2 cm/GW is returned compared to 5.7±0.5 cm/GW for KGW at the same wavelength

Tunable, CW laser emission at 225 nm via intracavity frequency tripling in a semiconductor disk laser

Numerous applications would benefit from a compact laser source with tunable, continuous-wave emission in the deep ultraviolet (wavelengths <250nm); however, very few laser sources have been demonstrated with direct emission in this spectral region and options are generally limited to pulsed, fixed wavelength sources or complex and impractical setups for nonlinear frequency mixing of the emission of several infrared lasers in various external enhancement cavities. Here we propose an all-solid-state, continuous-wave, tunable laser with emission between 224 nm and 226 nm via intracavity frequency tripling in an AlGaInP-based semiconductor disk laser (SDL). Output power up to 78 µW is achieved in CW operation, with a tuning range over 350 cm-1. AlGaInP-based SDLs may be designed to emit anywhere between ~640 – 690 nm such that wavelengths between 213 nm and 230 nm may be targeted for specific applications using a similar set-up. An in-depth study of the nonlinear conversion has been carried out to understand the limitations of the set-up, namely large walk-off angles for phase-matching in the nonlinear crystals, and the potential for increasing the output power to several milli-Watts. This is, to the authors' knowledge, the first implementation of intracavity frequency tripling in a visible SDL and the shortest wavelength emitted from an SDL system

Continuous-wave semiconductor disk laser emitting at 224 nm via intracavity frequency tripling

We present frequency tripling of a tunable continuous-wave red AlGaInP semiconductor disk laser. From a fundamental beam at 674 nm, output power up to ~100 μW and laser tunability over 1.8 nm are reported

GaN/InGaN-diode-pumped AlGaInP-based VECSELs with high spectral purity for quantum technology systems

The development of compact laser systems, especially those with emission at visible wavelengths, is key for the advancement of quantum technology systems, often required to have high performance in terms of stability, noise and linewidth. In this scenario, optically pumped vertical-external-cavity surface-emitting laser (VECSEL) technology has demonstrated great potential due to its higher brightness, lower noise, and narrower intrinsic linewidth operation when compared to other semiconductor laser technologies. Recently, we demonstrated sub-200 Hz operation of an AlGaInP-based VECSEL with emission at 689 nm with output power exceeding 150 mW, targeting the narrow red cooling transition of neutral strontium. Similar narrow linewidth performance was achieved when a high-power InGaN-GaN laser diode (LD) was implemented as the optical pump source for the VECSEL [2]. These blue/green-emitting LDs are key not only for the achievement of robust low noise operation via active pump control but also for the miniaturization of the visible VECSEL systems via pump laser integration to the overall packaging. In this talk, we review and outline the next steps for our research work on the development of compact, narrow linewidth diode-pumped AlGaInP-based VECSELs for application in neutral strontium optical clocks

Sub-kHz-linewidth VECSELs for cold atom experiments

We report and characterize sub-kHz linewidth operation of an AlGaInP-based VECSEL system suitable for addressing the narrow cooling transition of neutral strontium atoms at 689 nm. When frequency-stabilized to a standard air-spaced Fabry-Perot cavity (finesse 1000) via the Pound-Drever-Hall (PDH) technique, it delivers output power >150 mW in a circularly-symmetric single transverse mode with low frequency and intensity noise. The optical field was reconstructed from the frequency noise error signal via autocorrelation and the Wiener-Khintchine theorem, leading to an estimated linewidth of (125±2) Hz. Optical beat note measurements were performed against a commercial locked laser system and a second, almost identical, VECSEL system resulting in linewidths of 200 Hz and 160 Hz FWHM, respectively. To the best of our knowledge, this is the first demonstration of a VECSEL compatible with the narrowest of lines (few hundred Hz) used for cooling and trapping atoms and ions

Development of high performance, ultralow-noise VECSELs for optical lattice clocks

The development of high performance and stable lasers with ultra-low noise is critical for further advancement of quantum technologies, such as optical lattice clocks and atom interferometers In addition, as several lasers with different wavelength, brightness, and linewidth are required for such quantum systems, lasers are the major factor in not only the bulkiness and complexity of the technology but also the overall efficiency. Here, we present progress on the development of compact, ultra-low-noise, narrow-linewidth AlGaInP-based VECSELs with direct emission at 689 and 698 nm, of interest for neutral strontium optical clocks

1.6 W continuous-wave Raman laser using low-loss synthetic diamond

Low-birefringence (Δn<2x10−6), low-loss (absorption coefficient <0.006cm−1 at 1064nm), single-crystal, synthetic diamond has been exploited in a CW Raman laser. The diamond Raman laser was intracavity pumped within a Nd:YVO4 laser. At the Raman laser wavelength of 1240nm, CW output powers of 1.6W and a slope efficiency with respect to the absorbed diode-laser pump power (at 808nm) of ~18% were measured. In quasi-CW operation, maximum on-time output powers of 2.8W (slope efficiency ~24%) were observed, resulting in an absorbed diode-laser pump power to the Raman laser output power conversion efficiency of 13%