200W, 350Fs Fiber Cpa System Enabled By Chirped-Volume-Bragg-Gratings And Chirally-Coupled-Core Fiber Technology

Fiber-CPA-laser-systems are an extremely promising technology for generating ultrashort (fs-scale) pulses at high average-powers (hundreds-of-Watts to kW) while still producing diffraction-limited beams and being compact and robust compared to bulk-solid-state systems. Two obstacles still must be overcome to realize this potential, however. First, there is a need for stretchers and compressors that can yield long stretched pulse-durations (hundreds-of-ps to nanoseconds) and can handle high-energies and average-powers, yet are still simple and compact, so as to not offset the benefits of fibers. Secondly, large-core-fibers are needed for amplifiers and other components that are robustly singlemode. In this work, we present an Yb-fiber-CPA-system based on two novel technologies to overcome the aforementioned problems. Chirped-volume-Bragg-gratings (CVBGs), slabs of photo-thermo-refractive glass of cmscale with a quasi-periodic longitudinal index-of-refraction, are used for the stretcher and compressor. Their compactness and simplicity makes them compatible with fiber-laser benefits, and have excellent power handling capabilities are. Chirally-coupled-core (CCC) fibers, which have large core diameters (35μm here), yet are robustly single mode and can be coiled and spliced, are used for the power-amplifiers. Using these technologies, a system producing a record 200W of power (130W compressed) with 350fs pulse durations is demonstrated, and the potential kW-level-scaling is explored. © 2010 Copyright SPIE - The International Society for Optical Engineering

Incoherent combining of 100-W Yb-fiber laser beams by PTR Bragg grating

Volume diffractive gratings (Bragg gratings) in photo-thermo-refractive (PTR) inorganic glass are proposed for incoherent laser beam combining because they have narrow spectral selectivity and diffraction efficiency greater than 95 % from visible to near IR regions. They showed no laser-induced damage, no thermal lens, and no Bragg angle shift under CW Yb-fiber laser (1096 nm) irradiation at 100 kW/cm2. It opens the way to rugged, low-cost, efficient optics for high-power laser systems. Based on theoretical modeling of PTR Bragg gratings, we have designed a high-efficient technology for incoherent combining of two or several laser beams with certain wavelength shift. Two 100 W beams of Yb-fiber lasers in the range of 1080-1100 nm with the wavelength separation of 11 nm were combined with efficiency exceeding 75 % while material losses did not exceed 2-4%. No fading or parameter change of PTR Bragg grating working in two 100 W beams were found. It was found that the process limiting efficiency of incoherent beam combining is the spectral widening of radiation of Yb-doped fiber lasers. At high power, their spectral width exceeds spectral selectivity of Bragg grating and causes a decrease of diffraction efficiency

Volume chirped Bragg gratings - monolithic components for stretching and compression of ultrashort laser pulses

International audienceAn innovative type of optical component--a volume Bragg grating--has recently become available commercially and has found wide applications in optics and photonics due to its unusually fine spectral and angular filtering capability. Reflecting volume Bragg gratings, with the grating period gradually changing along the beam propagation direction (chirped Bragg gratings--CBGs) provide stretching and recompression of ultrashort laser pulses. CBGs, being monolithic, are robust devices that have a footprint three orders of magnitude smaller than that of a conventional Treacy compressor. CBGs recorded in photo-thermo-refractive glass can be used in the spectral range from 0.8 to 2.5 μm with the diffraction efficiency exceeding 90%, and provide stretching up to 1 ns and compression down to 200 fs for pulses with energies and average powers exceeding 1 mJ and 250 W, respectively, while keeping the recompressed beam quality M2<1.4, and possibly as low as 1.1. This paper discusses fundamentals of stretching and compression by CBGs, the main parameters of the gratings including the CBG effects on the laser beam quality, and currently achievable CBG specifications