Broadband and robust adiabatic second-harmonic generation by a temperature gradient in birefringently phase-matched lithium triborate crystal

TL;DR

This paper demonstrates a high-power, broadband, and efficient second-harmonic generation in lithium triborate crystal by inducing a temperature gradient to achieve adiabatic phase matching, surpassing traditional methods in bandwidth and power handling.

Contribution

It introduces a novel approach of using a temperature gradient in birefringently phase-matched lithium triborate for adiabatic second-harmonic generation, enabling high power and broad bandwidth.

Findings

Achieved 18°C temperature bandwidth, 5.4 times wider than fixed temperature.

Converted over 60% efficiency with a 0.9 mJ pump pulse.

Enabled high-power operation beyond quasi-phase matching limitations.

Abstract

Phase-matched nonlinear processes exhibit a tradeoff between the conversion efficiency and the acceptance bandwidth. Adiabatic nonlinear processes, in which the phase mismatch varies slowly along the interaction length, enable us to overcome this tradeoff, allowing an efficient frequency conversion with broad spectral and thermal bandwidths. Until now, the variation in the phase mismatch condition was mainly based on quasi-phase matching in ferroelectric crystals. However, this solution is limited to low power sources. Here, instead, we study the adiabatic second harmonic in birefringently phase-matched lithium triborate crystal, enabling us to handle much higher power levels. The variation in the phase mismatch is achieved by inducing a temperature gradient along the crystal. By using a 50 mm long crystal, the adiabatic process provided a temperature bandwidth of 18-celsius degrees, 5.4 times wider than what is achieved when the same crystal is held at the fixed phasematching temperature. The conversion efficiency exceeded 60% for a 0.9 millijoule pump pulse.