Fibre-coupled red diode-pumped Alexandrite TEM₀₀laser with single and double-pass end-pumping

Abstract

We report the investigation of an Alexandrite laser end-pumped by a fibre-coupled red diode laser module. Power, efficiency, spatial, spectral, and wavelength tuning performance are studied as a function of pump and laser cavity parameters. It is the first demonstration, to our knowledge, of greater than 1W power and also highest laser slope efficiency (44.2%) in a diodepumped Alexandrite laser with diffraction-limited TEM 00 mode operation. Spatial quality was excellent with beam propagation parameter M 2 ~ 1.05. Wavelength tuning from 737 -796nm was demonstrated using an intracavity birefringent tuning filter. Using a novel double pass endpumping scheme to get efficient absorption of both polarisation states of the scrambled fibredelivered diode pump, a total output coupled power of 1.66 W is produced in TEM 00 mode with 40% slope efficiency.

Analytical model of tunable Alexandrite lasing under diode end-pumping with experimental comparison

“…5, at crystal temperatures of 10 • C and 60 • C. The optimum wavelengths of 765 nm and 770 nm at 10 • C and 60 • C, respectively, are typical for Alexandrite [1,7,16]. Elevated temperatures extended the upper tuning range, as has been previously reported [2], but in turn increased the lower bound by 7 nm.…”

“…(27), with an approximate linear form. The optimum slope efficiency in Alexandrite is therefore highly likely to be from pump ESA effects and has been observed in previous work [6,7].…”

“…Recent advancements in high power red laser diodes has enabled efficient and multi-watt diode pumped operation [6,7]. The benefits of diode pumping include an order of magnitude increase in laser efficiency and the ability to more easily control the delivery of the pump energy to the gain medium, as in end pumping, achieving a better TEM 00 mode overlap [7]. Diode-pumped Alexandrite is a promising prospect as a tunable, high efficiency laser source for LIDAR [5], among other applications.…”

Temperature dependence of Alexandrite effective emission cross section and small signal gain over the 25-450 °C range

“…In the early years of its development, these favorable properties made Alexandrite the laser of choice in the development of flashlamp pumped high energy and high power Q-switched laser systems especially for biomedical applications. Over the last decade, the advancement of higher brightness laser and light-emitting diodes in the red spectral region, generated a renewed interest towards Alexandrite [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] and continuous-wave laser output powers above 25 W have already been achieved from compact diode-pumped systems [12]. Mode-locking of Alexandrite using Saturable Bragg Reflectors (SBRs) [26], Kerr-lensing [27,28], and graphene saturable absorbers [29] has also been demonstrated recently.…”

High Average Power Second-Harmonic Generation of a CW Erbium Fiber MOPA

“…The superior thermal and mechanical properties of Alexandrite over the colquiriites has enabled the CW power to be scaled to 26 W at 759 nm with multiple transverse modes, pumped by diode bars operating at 639 nm [8]. The highest reported near diffraction-limited CW power at 780 nm for Alexandrite is, however, only around the Watt-level [9].…”