Non-perturbative generation of DUV/VUV harmonics from crystal surfaces at 108 MHz repetition rate.

J. Seres,C. Serrat,E. Seres,T. Schumm

doi:10.1364/oe.26.021900

Abstract

We demonstrate non-perturbative 3rd (267 nm) and 5th (160 nm) harmonic generation in solids from a Ti:sapphire frequency comb (800 nm) at 108 MHz repetition rate. The experiments show that non-perturbative low harmonics are dominantly generated on the surface and on the interface between solids, and that they are not produced by bulk processes from the near-surface layer of the material. Measurements reveal that due to the lack of phase matching, the generated harmonics in bulk are suppressed by orders of magnitude compared to the signal generated on the surface. Our results pave the way for the development of all-solid-state high repetition rate harmonic sources for vacuum ultraviolet spectroscopy and high precision frequency comb metrology.

Highlights

High harmonic generation (HHG) is an attractive method to convert ultrashort laser pulses from the infrared or visible spectral range into the vacuum ultraviolet (VUV) or soft x-ray spectral range [1]
We demonstrate non-perturbative 3rd (267 nm) and 5th (160 nm) harmonic generation in solids from a Ti:sapphire frequency comb (800 nm) at 108 MHz repetition rate
Our results pave the way for the development of allsolid-state high repetition rate harmonic sources for vacuum ultraviolet spectroscopy and high precision frequency comb metrology

Summary

Introduction

High harmonic generation (HHG) is an attractive method to convert ultrashort laser pulses from the infrared or visible spectral range into the vacuum ultraviolet (VUV) or soft x-ray spectral range [1]. Harmonics can be generated at much lower laser intensities than in gases, promising the extension of HHG into very compact laser sources and with very high repetition rates, reaching even GHz frequencies. Several recent studies have suggested the need to further investigate the precise generation of harmonics in solids in order to accurately differentiate between bulk and surface generation, and between perturbative and non-perturbative processes. The spectrally resolved beam was detected with a VUV photomultiplier (Hamamatsu R6836), sensitive in the 115-320 nm spectral range, which prevented us from detecting the 7th or higher harmonic orders which would be present

Harmonic generation on fluoride crystals

Z-scan measurement on the fluoride crystals

Z-scan measurement on the GaN layer on sapphire

Conclusion