A compact optical parametric oscillator Raman microscope for wavelength-tunable multianalytic microanalysis


Pablo Londero, Department of Scientific Research, The Metropolitan Museum of Art, 1000 Fifth Avenue, New York, NY 10028-0198, USA.

E-mail: pablo.londero@metmuseum.org


We have developed a high-throughput microscope for wavelength-tunable microscopic studies of materials by Raman, surface-enhanced Raman, fluorescence, and reflectance spectroscopy. Narrow-band excitation over a broad tuning range (410–2200 nm) is provided by a solid-state, compact, and relatively inexpensive new class of diode-pumped Nd:YAG optical parametric oscillator emitting approximately 1-mJ, 10-ns pulses at a rate up to 100 Hz. Rayleigh rejection over the tuning range is obtained with an array of angle-tuned custom dielectric filters. Although high-power, low duty-cycle light sources have so far had only very limited use for tunable Raman and surface-enhanced Raman spectroscopy, we show that undesirable nonlinear effects that arise from the high peak power of the output can be mitigated to produce good results with the proper choice of additional microscope elements. Measurements can be performed across the visible range with 20% sample-to-detector throughput and 10 cm−1 resolution. The system is also fitted with a fiber optic imaging system to perform fluorescence and reflectance spectroscopy measurements with a spatial resolution of 5 µm. We demonstrate the instrument's analytical capabilities by recording resonance Raman and surface-enhanced Raman emissions from a commercial lake pigment and crystal violet, respectively, colorants of interest in cultural heritage studies and forensic science. We also isolate and measure the reflectance spectrum of a commercial lake pigment and the ultraviolet fluorescence spectrum of a single fiber of cochineal-dyed silk. The tunability, flexibility, compactness, and spatial resolution of the device provide novel capability for multianalytic materials research in fields such as forensic science and cultural heritage studies. Copyright © 2012 John Wiley & Sons, Ltd.