Diamond‐based concept for combining beams at very high average powers

Abstract

Ever since the laser's invention, there has been great interest in increasing beam output power without detriment to its coherence. Despite great advances having been obtained through the use of a diverse range of approaches, steady‐state beam powers above ten kilowatts remain a significant challenge for solid‐state lasers due to the heightened impact of detrimental nonlinear effects such as thermal lensing. Multiplexing several lasers using beam combination represents a method for surpassing the power barriers of single lasers. Here we propose and demonstrate a novel approach to beam combination and power scaling based on Raman conversion in diamond. Power from multiple non‐collinear pump beams is efficiently transferred onto a single Stokes beam in a single‐pass amplifier. Using three mutually‐independent nanosecond pulsed beams from a free‐running‐linewidth 1064 nm laser, 69% of the total peak pump power of 6.7 kW was transferred onto a TEM00 Stokes seed pulse at 1240 nm in a 9.5 mm long diamond crystal. Compared to other beam combination techniques, diamond beam combination has advantages of relaxed constraints on pump beam mutual coherence, while enabling narrowband output. Thermal considerations for extending from low duty‐cycle to continuous wave operation and higher power levels are discussed.

High Power Diamond Raman Lasers

“…This feature, a consequence of the freedom for phonons to take any k-vector owing to their flat dispersion relation [31], is the critical aspect that makes Raman lasers share many properties of inversion lasers and sets them apart from nonlinear wave mixing processes such as χ (2) parametric oscillators. This enables generation of high brightness output from low-beam-quality inputs [43], [44] and multiple non-collinear pumps (Raman beam combination) [45] as well as offering potential for side-pumped configurations [46].…”

“…2. Wavelength dependence of g R obtained using the following methods: pump probe (diamonds) [38], [45], [50]- [52]; SRS threshold (triangles) [9], [14], [23], [53]; spontaneous Raman scattering (squares) [11], [47]. Pump polarization parallel to: 111 (full symbols); 110 (open symbols); 100 (hatched symbols).…”

“…The Stokes seed power required for efficient extraction scales approximately linearly with the M 2 of the pump beam [79]. We have also studied Raman amplifiers with multiple non-collinear pump beams [45]. The effective beam overlap is reduced for angled beams, so that a higher seed power is required for a given extraction efficiency.…”

“…We have experimentally demonstrated a single-pass Raman amplifier using multiple incoherent pump beams [45]. Using three pump beams with a combined peak power of 6.1 kW, the pump power was depleted by 82% at the pulse peak, as shown in Fig.…”

“…For higher-power output, stable SLM output may be best achieved using master-oscillator power-amplifier configurations. It is interesting to note that, due to the finite Raman gain bandwidth, amplifiers pumped by multi-longitudinal-and multi-transverse-mode pump beams, and by multiple non-collinear beams [45], are expected to still enable efficient power transfer onto a spectrally narrowed and diffraction-limited seed beam.…”