Abstract
Two dimensional mid-infrared upconversion imaging provides unique spectral and spatial information showing good potential for mid-infrared spectroscopy and hyperspectral imaging. However, to extract spectral or spatial information from the upconverted images an elaborate model is needed, which includes non-collinear interaction. We derive here a general theory providing the far field of the upconverted light when two arbitrary fields interact inside a nonlinear crystal. Theoretical predictions are experimentally verified for incoherent radiation and subsequently applied to previously published data with good agreement.
Highlights
Sensitive mid-infrared imaging and spectroscopy is emerging as an attractive alternative to its more well-known visible or near-infrared counterparts within fundamental band gas analysis, spectral identification and quantification of complex molecules [1,2,3].Mid-IR detectors exist in different forms [4], but they are all limited by an unavoidable dark noise due to thermal radiation originating from the finite temperature of the detector itself [4]
High sensitivity mid-IR detectors need to be cooled to reduce noise. This is in strong contrast to visible (VIS) or near infrared (NIR) detectors where thermal radiation is much less pronounced at room temperature
This study focuses on 2-dimensional upconversion imaging of faint objects where depletion is irrelevant; to describe imaging adequately a model including arbitrary input fields is needed including non-collinear interaction of the incident beams
Summary
Sensitive mid-infrared (mid-IR) imaging and spectroscopy is emerging as an attractive alternative to its more well-known visible or near-infrared counterparts within fundamental band gas analysis, spectral identification and quantification of complex molecules [1,2,3]. High sensitivity mid-IR detectors need to be cooled to reduce noise This is in strong contrast to visible (VIS) or near infrared (NIR) detectors where thermal radiation (dark noise) is much less pronounced at room temperature. An attractive alternative to cryogenically cooled mid-IR detection and imaging is roomtemperature frequency upconversion followed by detection in the VIS or NIR region [5,6,7]. This method relies on a two stage procedure. To understand and exploit the attractive features of upconversion, a more elaborate model of the image formation is needed. Previous published results will be discussed and modeled using the developed theory
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