Cascaded multi-harmonic generation in a \b{eta}-BBO crystal reaching 133 nm from a single 800 nm pump beam

TL;DR

This paper demonstrates the generation of multiple cascaded harmonics up to the 6th order in a ta-BBO crystal using a single 800 nm laser, extending into the vacuum ultraviolet range, with potential spectroscopic applications.

Contribution

It is the first to show simultaneous generation of multiple cascaded harmonics up to the 6th order in ta-BBO crystal driven by a single 800 nm laser source.

Findings

Harmonics up to the 6th order are generated in ta-BBO crystal.

Harmonics are generated via cascaded : and : processes.

Even weak harmonics are significantly above noise, suitable for spectroscopy.

Abstract

Nonlinear crystals are widely used to efficiently generate second or third harmonics, and also for frequency mixing. Generation of multiple cascaded harmonics simultaneously, however, appears much less studied, although supported by the usually large nonlinearity of these crystals. Here, we demonstrate the generation of multiple harmonics up to 6th order in a \b{eta}-BBO crystal, extending into the vacuum ultraviolet spectral range. Phase matched generation of the second or the third harmonic is directly driven by a single 800 nm Ti:sapphire oscillator beam. Our study reveals that the harmonics are generated by \c{hi}(2):\c{hi}(2) and \c{hi}(2):\c{hi}(3) cascaded processes and intense harmonic signals are obtained even for the 5th and 6th harmonics, where the \b{eta}-BBO crystal is mostly absorbing. While higher order harmonics cannot be phase matched simultaneously, limiting the harmonic amplitudes, even the weakest harmonics are more than three orders of magnitude above the measurement noise limit, making them suitable for many spectroscopic applications.