Abstract
We report on a single-frequency fiber master oscillator power amplifier utilizing a polarization-maintaining step-index fiber with an Al/Ce/F core-glass composition doped with a very high Yb concentration (0.25 at.%). This design made it possible to use a very short fiber (~1 m) and to coil it in a tight radius (4 cm in the amplifier, while 2 cm gave similarly negligible bending loss) so that the packaged system is one of the most compact reported to date (~0.6 L). The use of a short fiber increased the threshold for stimulated Brillouin scattering well above 100 W while maintaining near-ideal beam quality. The fiber was pumped with a diode-pumped solid-state laser and cooled passively by spooling it on a grooved aluminum mandrel. The amplifier produced a strongly linearly polarized output at 1064 nm in the fundamental mode (M2 ≤ 1.2) with a 150 kHz linewidth and a power of 81.5 W for 107 W of launched pump power. No deleterious effects from the elevated thermal load were observed. The residual photodarkening loss resulting from the high Yb concentration, found to be small (~0.7 dB/m inferred at 1064 nm) with accelerated aging, reduced the output power by only ~20% after 150 h of operation.
Highlights
The development of high-power single-frequency Yb-doped laser sources has been stimulated by both scientific interest and industrial applications
High-power lasers with a narrow linewidth, very low relative intensity noise (RIN) [1], and high beam quality are required in applications such as high-precision resonant fiber sensors [2] and nonlinear optical conversion [3]
Power scaling in a single-frequency fiber master oscillator power amplifier (MOPA) is often limited by the onset of stimulated Brillouin scattering (SBS) in the gain fiber
Summary
The development of high-power single-frequency Yb-doped laser sources has been stimulated by both scientific interest and industrial applications. A technique that has been extensively studied to meet these requirements is the fiber master oscillator power amplifier (MOPA) It is composed of a seed laser followed by one or more amplification stages utilizing rareearth-doped fibers. Several effective techniques have been developed to suppress SBS Some of these techniques rely on modifying the modal or spectral properties of the seed laser [5,6,7,8]. Achieving output powers in excess of 100 W requires more than one mitigation technique [9,16] These techniques are essential when amplifying a signal with a linewidth narrower than the SBS gain bandwidth (~23 MHz in silica [17]), in which case the SBS threshold is low
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