Comparison of Three Compact Raman Systems with Excitation Laser Wavelengths of 405, 532, and 660 nm (µRA-RGB)

Figures & data

TABLE I Summary of Specifications for All Three µRA Systems

	Blue	Green	Red
Laser wavelength, type	405 nm ± 1 nm, diode	532 nm ± 1 nm, DPSS	660 nm ± 1 nm, diode
Laser power	200 MW	200 MW	175 MW
Spectrometer range, slit	430 to 530 nm, 100 µm	560 to 730 nm, 100 µm	770 to 920 nm, 100 µm
Excitation/collection fiber	5 m each; 100-µm single/100-µm six-around-one configuration (round to linear)
Acquisition mode	60 s (3 × 20 with averaging) per specification, three-channel (0.25 to 0.35 nm) moving average filter

DPSS = diode pumped solid state.

Fig. 1. Background spectra of all three µRA systems. The spectra displayed represent an averaged signal from approximately 5 days of measurement with 1 spectrum/min showing mainly the fluorescence signal of the optical path and reflections and fluorescence inside the sample volume. The position of relevant hydrogen isotope Raman signals is indicated.

Fig. 2. Response of each µRA system (red, green, and blue) to a varying D₂ pressure in the sample volume. Background is subtracted for better visibility of the Raman signal.

Fig. 3. SNR of all three µRA systems as a function of pressure showing a good linear response for all systems.

Fig. 4. LoD derived for a SNR ≥ 3 for all three µRA systems. For µRA-red, the structure in the background signal (Fig. 1) limits the LoD, especially for H_2.

Fig. 5. Comparison of µRA-green with the the LARA system.