The phrase "fiber laser" is a ubiquitous but insufficiently detailed description, as powers can range from microwatts to kilowatts. Fiber core diameters can vary from 3-micron core diameter ultra-high NA fibers for supercontinuum generation to 85 micron or greater PCF fibers to generate high pulse energies. With appropriate nonlinear optics, fiber lasers can reach wavelengths ranges from the UV to the LWIR and pulse widths can range from ultrafast femtosecond lasers to continuous output. The appropriate selection of laser can minimize cost, maximize efficiency, and ease assembly challenges in biomedical systems. The advantages and design limitations of single-mode, LMA, and PCF fiber lasers, as necessary to understand the available system impact of fiber laser source selection and including methods to reach directly inaccessible wavelength ranges, maximize net efficiency, or shape the light inside of a fiber are discussed.
Q-Peak Inc. has developed a Cr:ZnSe based femtosecond oscillator – power amplifier laser operating in the 2.5-μm region. The system generates 1 mJ per pulse at a 1-kHz repetition rate with a pulse duration of 184 fs, corresponding to a peak power of 5 GW. To the best of our knowledge this represents a record power for this spectral region. The highpeak power source utilizes a hybrid laser architecture, combining efficient fiber-laser pumping with solid state crystals. A Tm:fiber laser pumped, SESAM-initiated, Cr:ZnSe femtosecond oscillator provides a seed for chirped pulse amplification. The oscillator outputs 50-fs pulses that are stretched in a grating pulse stretcher and then amplified in a chain consisting of a regenerative amplifier and two stages of linear amplifiers all based on Cr:ZnSe. The pump power for amplification is provided by a Q-switched, high repetition rate, Ho:YLF laser, which in turn, is pumped by a high power Tm:fiber laser. The amplified pulses are compressed by a grating pulse compressor, resulting in 1 W of average power at a 1-kHz repetition rate. This laser system represents the state-of-the-art in short-pulse duration, pulse energy, and beam quality in this IR spectral range.
We report on the development of an all-fiber, 68-kW-peak-power, 16-ps-pulse-width, narrow-bandwidth, linearly polarized, 1064-nm fiber laser suitable for high-power, picosecond-pulse-width, green-light generation. Our 1064-nm fiber laser delivered an average power of up to 110 W at a repetition of 100- MHz in a narrow bandwidth, with minimal nonlinear distortion. We developed a high-power, picosecond green source at 532 nm through use of single-pass frequency-doubling of our 1064-nm fiber laser in lithium triborate (LBO). Using a 15-mm long LBO crystal, we have generated 30 W of average power in the second harmonic with 73-W of fundamental average power, for a conversion efficiency of 41%.
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