We consider the problem of 3D imaging spectroscopy on base of a pair of acousto-optical tunable filters (AOTFs). In such a system, quality of stereoscopic spectral images is the key factor influencing the accuracy of three-dimensional (3D) measurements and shape reconstruction. We analyze the image quality in a dual-channel AOTF-based spectrometer and proposed the optical scheme, which is free of image blur and has only aberrations of image distortion and drift. They can be eliminated by means of geometrical calibration of the imager. The optical characteristics of the system prototype are presented. The theoretical analyses and calculations of image aberrations are confirmed by experiments. The devices based on the dual-channel AOTF-based stereoscopic system may be effectively used for various 3D imaging spectroscopy applications.
Two methods of AOTF bandpass broadening are compared: multi-frequency generation and frequency-modulated ultrasound. The principal goal is to increase the optical throughput and signal-to-noise ratio of AOTF-based spectrometers. We present a simplified model of linear frequency-modulated mode, which make easy qualitative analysis of that operation model. Using the model we derived exact formulas for AOTF field-of-view and the total optical throughput raise with bandpass broadening and we found that AOTF field-of-view is much larger in the linear frequency modulation (LFM) mode. We conclude that for imaging applications of AOTF-based spectral elements, LFM mode of bandwidth control is more efficient than multi-frequency mode.
With the development of laser technology (for example, widespread use of diode pumping), the availability of powerful radiation sources is rising, which leads to an increase in demand for devices controlling powerful laser irradiation. The KGd(WO4)2 (short: KGW) crystal is one of the most famous due to a very high threshold of laser damage: up to 180 GW/cm2 for τ = 20 ns pulses . It is widely used in laser technics as lasing material. It was shown it has rather good acousto-optical properties, as well as the group of double potassium rare-earth tungstates KRE(WO4)2, where RE = Yb, Lu, and Y. It has been demonstrated for the first time that their AO figure of merit M2 is comparable with that of LiNbO3 and better than M2 of SiO2. Moreover, these monoclinic crystals are optically biaxial, transparent in visible and infra-red ranges (0.4-5.5 μm), and demonstrate significant anisotropy.
AOTF-based Spectral Imaging System for microscopic sample analysis in visible and NIR is described, characteristic features and some potential applications are discussed. Advantages of double AOTF configuration are analyzed