Note: A simple multi-channel optical system for modulation spectroscopies

J. Solís-Macías, J. D. Sánchez-López, R. Castro-García, J. M. Flores-Camacho, G. Flores-Rangel, Jian-Jhih Ciou, Kai-Wei Chen, Chang-Hsiao Chen, L. F. Lastras-Martínez, and R. E. Balderas-Navarro
Review of Scientific Instruments 88, 126107 (2017);, 2017.


Photoreflectance-difference (PR/PRD) and reflectance-difference (RD) spectroscopies employ synchronic detection usually with lock-in amplifiers operating at moderate (200–1000 Hz) and high (50–100 KHz) modulation frequencies, respectively. Here, we report a measurement system for these spectroscopies based on a multichannel CCD spectrometer without a lock-in amplifier. In the proposed scheme, a typical PRD or RD spectrum consists of numerical subtractions between a thousand CCD captures recorded, while a photoelastic modulator is either operating or inhibited. This is advantageous and fits the slow response of CCD detectors to high modulation frequencies. The resulting spectra are processed with Savitzky-Golay filtering and compared well with those measured with conventional scanning systems based on lock-in amplifiers.