Multichannel Hybrid Lock-In Amplifier for High-Resolution Broadband Raman Spectroscopy

Raman microscopy is a non-invasive and label-free spectroscopic technique with growing applications in the analysis of molecules and biological samples. Fast imaging requires the simultaneous acquisition of multiple wavelengths of the vibrational spectrum with high resolution <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\approx 10-100ppm)$</tex>. However, the design of a readout capable of combining high resolution and fast acquisition on many channels is still an open challenge. Here, we report a dual-mode, hybrid, multichannel instrument capable of acquiring a Raman spectrum in only <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$16\mu s$</tex> using analog differential lock-in amplifiers implemented in a custom CMOS chip. For slower measurements, a mixed analog-digital approach can be activated to enhance the signal-to-noise ratio by more than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20dB$</tex> compared to a fully analog mode. The system can operate in parallel on 76 channels with signals modulated up to 10MHz and an optical power down to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4uW$</tex> per channel.