Compact high-sensitivity symmetrical integrated optical system for the detection of Raman scattering with dual channels

We present here a compact symmetrical integrated optical system for the high-sensitivity handheld Raman spectrometer. This symmetric optical system is of higher sensitivity of Raman spectrum detection by coupling collection optics to the spectrometer directly, reflecting excitation laser incident at 45 degrees while efficiently passing the longer Raman-shift wavelength with two long-pass dichroic laser-flat beam-splitters placed in parallel. Three aspherical collecting lens with high-numerical aperture were used to collect Raman scattering. Four protected silver plane mirrors, two right-angle mirrors, and an aspherized achromatic focusing lens were used to focus Raman scattering into the slit on the collecting optical path. The Raman scattering light from the entrance slit were collimated to a blazed holographic reflective grating by an achromatic doublet lens, and the two diffraction lights with different orders were focused onto the two different surface of charge-coupled device with two broadband dielectric coating concave mirrors, respectively. The coma and astigmatism of this optical system are decreased by optimizing the optical structure parameters. The finer Raman spectrum of samples can be obtained through the second order diffraction spectrum acquisition channel, whereas the first order diffraction channel covers almost all the Raman spectrum range. The tested spectrum of Benzoyl peroxide indicates that this symmetric integrated optical system with three collecting channels and double-detecting channels has a higher sensitivity, higher signal-to-noise ratio, and finer Raman spectrum than the conventional portable Raman spectrometer with independent probe and single detection channel.