Non-Collinear Optical Parametric Amplifier

NOPA stands for Non-Collinear Optical Parametric Amplifier. It converts a single laser pulse into a tunable, ultrashort-pulse light source — the kind of tool that makes advanced photoemission spectroscopy possible. This system is driven by 20 µJ pulses at 1030 nm, with a repetition rate up to 2 MHz, and relies on several nonlinear phenomena working together: second-harmonic generation, supercontinuum generation, and optical parametric amplification.

How it works

  1. A beam splitter divides the incoming pulse into two paths.
  2. The reflected (S-polarized) beam is focused onto a BBO crystal to generate the second harmonic — the "pump" — at roughly 30% conversion efficiency.
  3. The transmitted (P-polarized) beam is focused into a YAG crystal, where the Kerr effect, self-focusing, and self-phase modulation broaden it into a white-light "seed" spectrum.
  4. The seed and pump beams overlap spatially and temporally in a second BBO crystal, amplifying a narrow, tunable, high-intensity output.
  5. The resulting (chirped) pulse is compressed with a prism pair to shorten its duration.

The result is a tunable light source (691–933 nm central wavelength) with the intensity and pulse duration needed to drive photoemission spectroscopy — revealing the electronic structure of materials that absorb in this range.

Schematic adapted from the doctoral thesis of Emanuel Wittmann — read it here.