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

Abstract

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.

Sub-kHz-linewidth VECSELs for cold atom experiments

“…The VECSEL gain structure used to achieve narrow linewidth operation is similar to those reported previously by our group [32,33]. The first component of the structure, grown on a GaAs substrate, is a semiconductor mirror (distributed Bragg reflector) composed of AlGaAs/AlAs layers with high-reflectivity at 690 nm.…”

“…Further, we see no reason why this performance could not be readily translated to any other wavelength within the broad range available to VECSELs systems, i.e. from the ultraviolet to the mid-infrared via a combination of semiconductor bandgap engineering and second harmonic generation achieved within the same, stabilized cavity (see e.g [33].). The fundamental, or Schawlow-Townes-Henry, limit for an AlGaInP VECSEL is expected to be 10 −4 Hz (calculated following [50]), orders of magnitude lower than any other semiconductor laser technology.…”

“…Laser oscillation is achieved by optically-pumping the gain structure with a compact, commercial semiconductor laser system at 532 nm (with power up to 5 W) in a 90-µm-diameter focal spot. The VECSEL emission wavelength is tuned to the correct value with sub-pm precision by using both the intracavity BRF and small changes to the sample temperature [33]. The former provides coarse tunability in steps of 200 pm when rotated in its axis, related to the free spectral range of the heat spreader; the latter allows fine, continuous tuning of the wavelength within the free spectral range of the BRF (30 pm).…”

Sub-kHz linewidth VECSEL for cold atom experiments

“…Here we report frequency stabilisation of an AlGaInPbased VECSEL locked to a standard commercial air-spaced Fabry-Perot cavity, achieving sub-kHz linewidth with powers up to 170 mW. The emission wavelength can be tuned from 685 to 693 nm, suitable for use as part of Strontium cold atom experiments; specifically for targeting the second-stage cooling transition used for Strontium magneto-optical traps: 689.4488968 nm (7.6 kHz) [5,7].…”

“…Potential for miniaturization is another attractive feature as these lasers are compact, with any frequency conversion and filtering performed intracavity. Linewidths of a few kHz have been demonstrated over timescales of the order of 1s [2,4,5], but sub-kHz linewidths, such as those required for narrow atom cooling and clock transitions, have yet to be reported. Here we report frequency stabilisation of an AlGaInPbased VECSEL locked to a standard commercial air-spaced Fabry-Perot cavity, achieving sub-kHz linewidth with powers up to 170 mW.…”