KEYWORDS: Upconversion, Crystals, Black bodies, Thermal imaging cameras, Temperature metrology, Matrices, Thermography, Quantum reading, Quantum noise, Signal to noise ratio
We present a scheme for estimating the noise-equivalent temperature difference (NETD) of frequency upconversion detectors (UCDs) that detect mid-infrared (MIR) light. In particular, we investigate the frequency upconversion of a periodically poled crystal based on lithium niobate, where an MIR conversion bandwidth of 220 nm can be achieved in a single-poled period by a special design. Experimentally, for an MIR radiating target at a temperature of 95°C, the NETD of the device was estimated to be 56 mK with an exposure time of 1 s. Meanwhile, a direct measurement of the NETD was performed utilizing conventional methods, which resulted in 48 mK. We also compared the NETD of our UCD with commercially available direct MIR detectors. We show that the limiting factor for further NETD reduction of our device is not primarily from the upconversion process and camera noise but from the limitations of the heat source and laser performance. Our detectors have good temperature measurement performance and can be used for a variety of applications involving temperature object identification and material structure detection.
The disturbance of atmospheric turbulence during laser transmission is a major problem in the field of high-energy laser transmission and communication. Fast and real time wavefront sensing is one of the key technologies in adaptive optical systems. For laser emission or communication systems with relatively smaller optical apertures and transmission distances, atmospheric aberration is mainly composed of low-order Zernike modes with weak intensity. Traditional Hartmann wavefront sensor works by regional segmentation and reconstruction of the wavefront plane, which need complicated matrix calculation, inducing considerable time delay. Its application in laser wavefront sensing can be technically sophisticated and redundant. Holographic modal wavefront sensing technology takes advantage of parallel modal detection method to obtain the intensity of specific modes of aberrations carried by the laser directly. With benefits of higher speed, smaller time delay, and compact system structure, it may be more suitable for atmospheric laser wavefront sensing. Here, we carried out simulation research on holographic modal wavefront sensor and its application in atmospheric laser wavefront sensing, the measuring accuracy and validation frontier of this technology are analyzed. The result provided informative support on high speed laser aberration sensing and correction.
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