Characterization Of Chirped Volume Bragg Gratings - Compact Laser Pulse Compressors

Increase in energy of ultrashort (picosecond, femtosecond) laser pulses is typically based on chirped pulse amplification (CPA) method. The nanojoule energy pulses are temporally stretched by several orders of magnitude prior amplification. The peak power is significantly decreased and the gain saturation and detrimental nonlinear optical effects, leading to the beam degradation, are avoided. Amplified pulses are compressed close to the initial pulse duration. Pulse stretching and compression requires special optical devices. In this work, we tested novel compact pulse compressors based on chirped volume Bragg gratings (CVBG), a piece of glass of few cm(3) in volume with continuously changing refractive index modulation period. Four CVBGs were analysed by a continuous-wave narrow-bandwidth laser tunable in wavelength between 1028 and 1032 nm, i.e. the bandwidth of our high-power picosecond lasers having active gain medium of ytterbium doped yttrium aluminium garnet (Yb:YAG). Spectrally resolved diffraction efficiency, beam quality, and angular chirp were measured on a beam reflected by the CVBGs.