A multi-channel, reconfigurable
fiber-coupled Raman instrument uses
fiber optic switches for
laser and calibration light routing to facilitate automated calibration, diagnosis and
operational safety. The
system allows
wavelength axis calibration on all channels;
laser wavelength calibration (including multiple and / or
backup laser options);
fiber coupling optimization; fault detection / diagnosis; and
CCD camera binning setup. In the preferred embodiment, dedicated calibration channels surround data channels on a 2-dimensional CCD dispersed slit image implemented using a unique cabling architecture. This “over / under” calibration interpolation approach facilitates quasi-simultaneous or sequential calibration / data acquisitions. CCD binning between sequential calibration and data acquisitions enables higher density multi-channel operation with tilted images based upon a multiplexed
grating configuration.
A diamond sample is used as a Raman shift reference for laser calibration, preferably in the form of a small disc sampled with an edge-illuminating probe using two unfiltered fibers. Detection of beam transmitted through the
diamond reference is also used to optimize laser
coupling efficiency with motion servos. An “intrinsically safe” laser
interlock circuit also serves as
current source for probe head “laser on”
diode indicator. The integrity of key components is monitored through strategically placed photodiodes positioned, for example, at fiber bends to detect light leakage from bent fiber as
verification of commanded laser path through fiber switches and at
neon and
halogen lamp locations to verify lamp operation. The optical switches used for calibration may also be configured for use as a laser
shutter.