Signal Enhancement Device for Use with Small Area Photocathodes in Raman Spectroscopy
During the past few years significant advances have been made in reducing various noise levels in laser Raman spectroscopy. Particularly striking improvements include the reduction in stray light by using double monochromators,1–3 decreased ghost intensities by interferometrically controlling the grating ruling engines, improved detection methods4–6 and substantial reduction in dark noise by appropriate tube design,7 and by using small area photocathode surfaces.7,8 In this connection we now use an ITT FW130 photomultiplier tube equipped with a slit-shaped (1.0 × 0.1 mm) S-20 photocathode mounted in a TE-104 Products for Research Inc. thermoelectrically coolable (to − 25°C) tube holder. In this chamber, however, the cathode surface is about 2.6 in from the exit slit and the bulk of the rays diverging from the exit slit fail to impinge upon the photocathode and are irretrievably lost.
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