Spectroscopic Imaging Using Acousto-Optic Tuneable Filters

Abstract

We report on a novel hyper-spectral fluorescence imaging filter-module based on an acousto-optic tuneable filter (AOTF). The AOTF functions as a full-field tuneable bandpass filter which offers fast continuous or random access tuning with high filtering efficiency. Due to the diffractive nature of the device, the unfiltered zeroorder and the filtered first-order images are geometrically separated. The module developed exploits this feature to simultaneously route both the transmitted whitelight image and the filtered fluorescence image to two separate cameras. Incorporation of prisms in the optical paths and careful design of the relay optics in the filter module has overcome a number of aberrations inherent to imaging through AOTFs, leading to excellent spatial resolution. A number of practical uses of this technique, both for in vivo auto-fluorescence endoscopy [1] and in vitro fluorescence microscopy [2] were reported. We will describe the operational principle and design of two recently improved prototype instruments for fluorescence-based diagnostics and will demonstrate their performance by presenting challenging hyper-spectral fluorescence imaging applications. [1] Mounir Bouhifd, Maurice P Whelan, Marc Aprahamian "Fluorescence imaging spectroscopy utilising acousto-optic tuneable filters" Proc. SPIE Int. Soc. Opt. Eng. 5826, 185-193 (2005) [2] Mounir Bouhifd, Maurice P. Whelan, Marc Aprahamian "Use of acousto-optic tuneable filters for imaging fluorescence spectroscopy applications in vivo and in vitro" Proc. SPIE Int. Soc. Opt. Eng. 5692, 11-20 (2005)