Nonlinear crystals for imaging and detection of mid-IR radiation

The mid-IR wavelength range, i.e. 2-25 μm, houses the vibrational spectra of most gasses and large molecules found in complex structures such as tissue, plastics or food. When designing an upconversion system for imaging or mid-IR detection, several aspects should be considered. Upconversion has several advantageous features which makes it an interesting option to consider for many mid-IR applications. Main advantages include, low-noise detection even at elevated temperatures, an almost instantaneous response time, phase preservation, and the ability to perform upconversion imaging. The χ⁽²⁾ crystal properties impact the performance of the system significantly. Design aspects related to the choice of crystal as well as different applications is presented.