Temperature-tunable UV generation using an Alexandrite laser and PPLN waveguides.

We present a simple and novel technique for achieving ultra-violet (UV) wavelength-tunable laser operation in the continuous-wave regime. Wavelength tunable operation in the near infrared is obtained from a compact two-mirror Alexandrite laser cavity by temperature tuning of the laser crystal. Second-harmonic-generation to the UV is then achieved at 376-379 nm and 384-386 nm by temperature tuning of a periodically-poled lithium-niobate (PPLN) waveguide. A maximum UV power of 1.3 mW from 185 mW infra-red pump throughput is obtained from a third-order PPLN Λ=6.1µm grating. These results show promising potential for simple and wavelength tunable access to wavelengths at 360-400 nm.

Pump-induced lensing effects in diode pumped Alexandrite lasers.

It is essential to understand the pump-induced lensing and aberration effects in solid-state lasers, such as Alexandrite, since these set limits on laser power scaling whilst maintaining high spatial TEM00 beam quality. In this work, we present direct wavefront measurements of pump-induced lensing and spherical aberration using a Shack-Hartmann wavefront sensor, for the first time, in a diode-pumped Alexandrite laser, and under both non-lasing and lasing conditions. The lens dioptric power is found to be weakly sub-linear with respect to the absorbed pump power, and under lasing, the lensing power is observed to decrease to 60 % of its non-lasing value. The results are inconsistent with a thermal lens model but a fuller theoretical formulation is made of a combined thermal and population lens model giving good quantitative agreement to the observed pump power dependence of the induced-lensing under non-lasing conditions and the reduced lensing under lasing conditions. The deduced value for the difference in excited to ground state polarizability is consistent with prior measurement estimates for other chromium-doped gain media. The finding of this paper provide new insight into pump-induced lensing in Alexandrite and also provides a basis for a fast saturable population lens mechanism to account for self-Q-switching observed recently in Alexandrite laser systems.

Tunable, dual wavelength and self-Q-switched Alexandrite laser using crystal birefringence control.

We present a red-diode-pumped Alexandrite laser with continuous wavelength tunability, dual wavelength and self-Q-switching in an ultra-compact resonator containing only the gain medium. Wavelength tuning is obtained by varying the geometrical path length and birefringence by tilting a Brewster-cut Alexandrite crystal. Two crystals from independent suppliers are used to demonstrate and compare the performance. Wavelength tuning between 750 and 764 nm is demonstrated in the first crystal and between 747 and 768 nm in the second crystal. Stable dual wavelength operation is also obtained in both crystals with wavelength separation determined by the crystal free spectral range. Temperature tuning was also demonstrated to provide finer wavelength tuning at a rate of -0.07 nm K -1. Over a narrow tuning range, stable self-Q-switching is observed with a pulse duration of 660 ns at 135 kHz, which we believe is the highest Q-switched pulse rate in Alexandrite to date. Theoretical modelling is performed showing good agreement with the wavelength tuning and dual wavelength results.

Unidirectional single-frequency operation of a continuous-wave Alexandrite ring laser with wavelength tunability.

High resolution spectroscopy, metrology and quantum technologies (e.g. trapping and cooling) require precision laser sources with narrow linewidth and wavelength tunability. The widespread use of these lasers will be promoted if they are cost-effective, compact and efficient. Alexandrite lasers with a broad tuning band pumped efficiently by low-cost red diodes are a potential candidate, but full performance as a precision light source has not been fully achieved. We present in this work the first continuous-wave (CW) and single-frequency operation of a unidirectional diode-end-pumped Alexandrite ring laser with wavelength tunability. An ultra-compact bow-tie ring cavity is developed with astigmatic compensation and a novel 'displaced mode' design producing CW output power > 1 W in excellent TEM00 mode (M2 < 1.2) when using a low brightness pump (M2 ≥ 30). Wavelength tuning from 727 - 792 nm is demonstrated using a birefringent filter plate. This successful operation opens the prospects of precision light source applications.