"TOPAS" Scheme

"TOPAS" consists of an independently pumped superfluorescence generator, three preamplifiers, and power amplifier. All these stages are geometrically arranged using a single nonlinear crystal. The seed signal is produced in low-energy preamplifiers, that are optimized for the best spectral and spatial filtering properties. The power amplifier uses <90% of the pump energy and is adjusted for high conversion efficiency along with the beam quality and duration of the converted pulses. To achieve high reproducibility of generated pulses, all the amplification stages are driven to saturation. At each stage, the pump energies and intensities are adjusted for the particular pump pulsewidth and power used.

Wavelength tuning

The tuning range of "TOPAS" is restricted mainly by the pump wavelength and IR-absorption edge of the particular nonlinear crystal (BBO or LBO). This range is notably extended by the frequency up- and down-conversion of the "TOPAS" output. Different frequency mixing schemes allow for continuous tuning across the whole accessible wavelength range and for generation of several synchronous pulses at different wavelengths.

The operation of "TOPAS" has been tested when pumped with 200-fs and 1-ps second-harmonic pulses of Nd:glass laser, 30-ps third-harmonic pulses of Nd:YAG laser, 25-fs to 3-ps fundamental and 1-2.5 ps second-harmonic pulses of Ti:saphire laser. In all the cases energy conversion into the parametric radiation up to 20-40% was achieved. An important feature of "TOPAS" design is that it can be matched to pump sources with peak power ranging over orders of magnitude. The minimum 150 fs pump pulse energy ensuring >5% parametric conversion is around 150 μJ. There are no limitations for pulse repetition rate up to several kilohertz.

"TOPAS" tuning