DFG-based mid-IR laser system for muounic-hydrogen spectroscopy

Abstract

The goal of this work is to prove the feasibility of building a laser system that can generate mid-infrared radiation with the parameters required for the measurement of the hyperfine splitting in the ground state of the mounic hydrogen spectroscopy. The first experimental results of a very straightforward scheme that, to our knowledge, has not been considered in the literature, are presented. We study a laser test bench system emitting nanosecond pulses of infrared tunable radiation in the spectral range 6.78 μm with high energy and narrow line-width, based on direct difference frequency generation (DFG), in non-oxide nonlinear crystals, using as pump lasers a single-mode Nd:YAG laser and tunable narrowbandwidth Cr:forsterite laser. The investigated system is based on lithium thioindate (LiInS 2 ) and silver thiogallate (AgGaS 2 ) crystals cut for type II difference frequency generation. The pulses of the Nd:YAG laser (1,064 μm) are combined with the pulses at ~ 1.262 μm of the Cr:forsterite laser through a dichroic mirror and sent to the nonlinear crystals in different optical geometries. The generated radiation reaches an output energy up to 80 μJ in a single pass optical geometry, has 10 ns long pulses at 50 Hz frequency repetition rate and is tunable in the range 6595 – 6895 nm. These first results prove the suitability of such an approach for building the laser system for the muonic-hydrogen experiment.