Multipass cell for gas analysis using a coherent optical source
A multi-pass gas cell that operates with reflected radiation pass through a gas, the reflected radiation transmitted and received by first and second fiber optic ports that are subject to an alignment adjustment, and a mirrored viewing window having a inner reflective surface exposed to an interior of the elongated cell body for reflecting the radiation within the cell body, an outer viewing surface, and a transmittance characteristic that permits a portion of the radiation to pass through the mirrored window, from the inner reflective surface to the outer viewing surface, as a visual indicator of the alignment condition of the reflected radiation relative to the first and second fiber-optic ports.
1. A multi-pass gas cell comprising:
a cell body configured for allowing a gas to be analyzed to pass therethrough under high pressure, high temperature, or both;
a first fiber-optic port for transmitting radiation into the cell body;
means for adjusting an alignment condition of the fiber-optic input;
a mirrored window having a inner reflective surface exposed to an interior of the elongated cell body for reflecting the radiation within the cell body;
a second fiber optic port for receiving the radiation reflected by the mirrored window and outputting it for analysis; and
the mirrored window further having an outer surface and a transmittance characteristic that permits a portion of the radiation to pass through the mirrored window as a visual indicator of the alignment condition of the reflected radiation relative to the first and second fiber-optic ports.
2. The multi-pass gas cell of claim 1 wherein the mirrored window comprised a reflecting spot that corresponds to an aligned condition of the fiber-optic input.
3. The multi-pass gas cell of claim 2 wherein the reflecting spot is a single reflecting spot located in the center of the mirrored window.
4. The multi-pass gas cell of claim 1 wherein the mirrored window has the whole of its inner reflective surface coated with a reflective coating that is partially transmissive.
5. The multi-pass gas cell of claim 1 wherein the radiation used for alignment is different then the radiation used for measurement.
6. The multi-pass gas cell of claim 1 wherein the radiation used for alignment is a coherent laser beam.
7. The multi-pass gas cell of claim 6 wherein the first and second fiber-optic ports are formed from an outer assembly comprising an adjustable collimator holder and an inner, interchangeable assembly comprising a collimator lens.
8. The multi-pass gas cell of claim 7 wherein a first inner assembly is used for coherent radiation suitable for visual alignment and wherein a second inner assembly is used with radiation suitable for analysis.