Antimonide disk lasers achieve multiwatt power and a wide tuning range

Abstract

The absorption lines of many environmentally important gases are found within the λ = 2–3μm wavelength range. Combined with the presence of an appropriate atmospheric window, these spectral lines represent useful diagnostics for gas spectroscopy,1 remote sensing, research in the life sciences, and free-space optical communications. Certain applications, such as laser-based tissue welding, require multiwatt optical sources with high beam quality, while others would benefit from light emitters generating ultrashort optical pulses (e.g., laser radar and freespace communications). Gallium antimonide (GaSb)-based semiconductor disk lasers2 (sometimes called vertical-external-cavity surface-emitting lasers or VECSELs) could offer a new, compact, and cost-effective alternative for use with the 2–3μm spectral window, which is currently covered by solid-state and fiber lasers as well as optical parametric sources. The VECSEL design combines power scalability and excellent beam quality with wavelength flexibility that is offered by the semiconductor gainmaterial. Additional optical elements can be used inside the laser resonator for spectral control, frequency conversion, and mode locking to produce ultrashort optical pulses. The gain mirror, deposited onto a GaSb substrate, consists of thin semiconductor films that make up a high-reflectivity Bragg mirror and a gain region. It is typically pumped at an angle using low-cost, poor-beam-quality laser-diode bars. We deployed a transparent diamond heat spreader to cool the gain region efficiently under intense optical pumping (see Figure 1). Our aim was to demonstrate generation of multiwatt output power, an extended tuning range, and short pulses near 2μm. All gain structures were grown monolithically by solid-state Figure 1. Schematic presentation of a semiconductor disk laser with a simple linear cavity. The smaller arrows indicate the direction of heat flow.