Schematics of interaction between the pump beam and Stokes beam through a molecule with a vibrational energy level (a) and intensity modulation of the beams induced by Raman loss and gain (b). The left panel of (a) illustrates the detection of a single vibration of the molecule with the monochromatic pump and Stokes beams in conjunction with the molecular vibrational levels. The right panel of (a) illustrates our multiplex detection of the molecular vibrations with the broad-band pump beam and monochromatic Stokes beam.
Schematics of optical setup (a) and measurement system for spectral imaging by the multi-channel lock-in amplifier (b). (a) The red line indicates the Stokes beam at 800 nm, and the yellow line is the white pump beam. ISO: isolator that rejects backing scattered or reflected light; BS1: beam splitter for the Stokes and pump line; VND: variable neutral density filter to adjust power; HWP: half-wave plate that optimizes the polarizing plane; PCF: photonic crystal fiber; DM: dichroic mirror; OL: objective lens; CL: collector lens; PZS: piezo scanning stage; SPF: short-pass filter to reject the Stokes beam; BS2: beam splitter used to observe a sample and beam spots; BS3: beam splitter for epi-Köhler illumination; LED: light-emitting diode for epi-Köhler illumination; and CCD: charge-coupled device used to confirm the overlap of the beams and take photos of the samples. (b) SP: spectrograph; FB: fiber bundle; APDs: 128 avalanche photo diodes biased at 140 V; PAs: 128 107 gain transimpedance pre-amplifiers; MLA: 128-channel multi-channel lock-in amplifier; and PC: personal computer.
The bright line spectrum from the neon tube with the 250-μm entrance-slit width on the spectrograph (a) and the correction curve (b). (a) The peak wavelengths of the neon bright lines are labeled on the corresponding bands, and (b) the dots represent the relationship between the peak channels estimated by fitting the Gauss function and the peak wavelengths. The red line is the calibration curve.
Spectrum of the white pump beam through the dichroic mirror (a); light noise spectra in 0–12.5 MHz (b); in 0–1.25 MHz (c); and in 0–12.5 kHz (d).
Stimulated Raman loss spectra of polystyrene (PS), polymethylmethacrylate (PMMA), and cyclohexane observed with the system constructed in this study (a) and spontaneous Raman spectra of the same samples (b).
The Raman loss spectra of cyclohexane at various Stokes beam powers (a); the relationship between the Raman loss signal at the 65th channel (the strongest peak of cyclohexane) and the power (b); the Raman loss spectra of cyclohexane diluted by carbon tetrachloride at various concentrations (c); and the relationship between the Raman loss signal at the 65th channel and the concentration.
CCD image of the 4-μm PS beads (10 × 10 μm area) (a); image of the same area constructed on the summation of the signals of the 40–50th channels (b); and the averaged spectrum of the spectra at the centers of the beads (indicated by the orange marks in (b)) (c).
CCD image of the mixed polymer film of PS and PMMA (20 μm × 20 μm area) (a); image of the same area based on the summation of the signals of the 40–50th channels (3103–3033 cm−1 Raman shift) (b); image based on the summation of the 55–65th channels (2998–2930 cm−1) (c); averaged spectrum in the area of the strong signals of the 40–50th channels (surrounded by the green square) (d); and the averaged spectrum in the area of the strong signals of the 55–65th channels (surrounded by the red square) (e).
Wavelengths of bright lines from the neon tube and estimated channels at the lines’ peak.
RMS electrical noise and RMS intensity noise of white pump beam.
Article metrics loading...
Full text loading...