Abstract
A complementary metal-oxide semiconductor (CMOS) lock-in pixel to observe stimulated Raman scattering (SRS) using a high speed lateral electric field modulator (LEFM) for photo-generated charges and in-pixel readout circuits is presented. An effective SRS signal generated after the SRS process is very small and needs to be extracted from an extremely large offset due to a probing laser signal. In order to suppress the offset components while amplifying high-frequency modulated small SRS signal components, the lock-in pixel uses a high-speed LEFM for demodulating the SRS signal, resistor-capacitor low-pass filter (RC-LPF) and switched-capacitor (SC) integrator with a fully CMOS differential amplifier. AC (modulated) components remained in the RC-LPF outputs are eliminated by the phase-adjusted sampling with the SC integrator and the demodulated DC (unmodulated) components due to the SRS signal are integrated over many samples in the SC integrator. In order to suppress further the residual offset and the low frequency noise (1/f noise) components, a double modulation technique is introduced in the SRS signal measurements, where the phase of high-frequency modulated laser beam before irradiation of a specimen is modulated at an intermediate frequency and the demodulation is done at the lock-in pixel output. A prototype chip for characterizing the SRS lock-in pixel is implemented and a successful operation is demonstrated. The reduction effects of residual offset and 1/f noise components are confirmed by the measurements. A ratio of the detected small SRS to offset a signal of less than 10−5 is experimentally demonstrated, and the SRS spectrum of a Benzonitrile sample is successfully observed.
Highlights
Developments in optical imaging techniques enable better understanding of the microscopic world
The reduction effects of residual offset and 1/f noise components are confirmed by the measurements
The remainder of this paper describes the proposed image sensor and measurement results in detail
Summary
Developments in optical imaging techniques enable better understanding of the microscopic world. Raman scattering, has long been explored to provide a contrast mechanism for label-free, noninvasive imaging to study biological samples by detecting specific vibrational spectra of chemical bonds [1,2]. Spontaneous Raman scattering microscopy possesses the relatively high spatial resolution capability. Due to the extremely small Raman cross section, the spontaneous Raman scattering microscopy requires a lengthy acquisition time and is not suitable for live imaging [3]. Coherent Raman scattering (CRS) microscopy enhances the Raman response significantly, which facilitates high-speed imaging. The CRS utilizes two laser sources, pump beam at frequency ωp and Stokes beam at frequency ωs , to coincide on the sample. When the Sensors 2016, 16, 532; doi:10.3390/s16040532 www.mdpi.com/journal/sensors
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
