Tunable infrared upconversion module for the 1.9 to 5.5 µm range.

In this Letter, an efficient tunable upconversion module is demonstrated and characterized. The module combines high conversion efficiency and low noise with broad continuous tuning, covering the spectroscopically important range from 1.9 to 5.5 µm. A fully computer-controlled, compact, portable system is presented and characterized in terms of efficiency, spectral coverage, and bandwidth, using simple globar illumination. The upconverted signal is in the 700-900 nm range, ideal for Si-based detection systems. The output from the upconversion module is fiber coupled, enabling flexible connection to commercial NIR detectors or NIR spectrometers. In order to cover the spectral range of interest using periodically poled LiNbO3 as the nonlinear material, poling periods ranging from 15 to 23.5 µm are needed. The full spectral coverage is reached using a stack of four fanned poled crystals, enabling maximal upconversion efficiency of any spectral signature of interest in the 1.9 to 5.5 µm range.