Comparison of Acousto-Optic and Liquid Crystal Tunable Filters for Laser-Induced Breakdown Spectroscopy

In this paper, we report the first time-resolved laser-induced plasma images acquired using a liquid crystal tunable filter (LCTF). We also compare the use of LCTFs and acousto-optic tunable filters (AOTFs) for time-resolved plasma imaging applications in terms of resolution, out-of-band rejection, and image quality. Application of tunable filter technologies to plasma imaging is unlike other spectroscopic imaging methods because of the intense and spectrally broad background generated by a laser-induced plasma. High quality images of the distribution of atomic emission within a laser-induced plasma can be achieved using both AOTFs and LCTFs. However, additional filters are needed for rejection of wavelengths outside the tuning ranges of the devices. Both devices exhibited superior resolution in the lower working range of the filters (∼500 nm) with the LCTF exhibiting superior spectral resolution to the AOTF.