Visible 20-femtosecond pulse generation by double-pass non-collinear optical parametric amplifier.

We report a new design and construction of a highpower, white light seeded double-pass non-collinear optical parametric amplifier (NOPA) in the visible wavelength using a single amplifier crystal. For its successful implementation, many important practical considerations are discussed in detail. Tunable femtosecond pulses were obtained with pulse widths less than 20 fs and characterized using frequency-resolved optical gating technique. The generated visible pulse, tunable from 490 to 740 nm from the NOPA, was further optimized by second harmonic and four-wave mixing signals. [ABSTRACT FROM AUTHOR]