Single-fiber resonance-enhanced Raman spectroscope
We have designed a Raman instrument able to use a single
optical fiber compatible with standard endoscopes.
Based on the absorption spectrum of β-carotene (BC; Fig. 1),
an excitation laser (Spectra-Physics model 163) at 488 nm
was chosen for this prototype. As shown in Fig. 2, the laser
light is launched into a multimode optical fiber patch cable
(SMA-connectorized 300-μm polymer-clad silica fiber;
3M). This excitation fiber is then connected to a custommade
optical module via a collimator and gimbal mount.
The collimated laser light is directed into a custom-made
holographic optical element (Ralcon Development Lab)
at an angle such that it is diffracted toward a lens focusing
the light into a SMA-connectorized endoscopy probe fiber
(200- to 600-μm polymer-clad silica fiber, 0.22-0.48
numerical aperture, with Tefzel jacket) that is flat-cut and
polished flush with the jacket to make it compatible
with most endoscope channels. The probe fiber serves
both as an excitation fiber and as a scattered light collection
fiber, directing the back-scattered light toward
the optical module where it is collimated and passed
through the holographic optical element. The considerable
Rayleigh scattered light (light that has not been
wavelength shifted via the Raman effect) from the tissue
is diffracted out of the collimated beam by the holographic
optical element, whereas the Raman-shifted light (and
tissue fluorescence, etc.) is selectively passed through
the holographic optical element to another lens, which
Single-fiber resonance-enhanced Raman spectroscopeWe have designed a Raman instrument able to use a singleoptical fiber compatible with standard endoscopes.Based on the absorption spectrum of β-carotene (BC; Fig. 1),an excitation laser (Spectra-Physics model 163) at 488 nmwas chosen for this prototype. As shown in Fig. 2, the laserlight is launched into a multimode optical fiber patch cable(SMA-connectorized 300-μm polymer-clad silica fiber;3M). This excitation fiber is then connected to a custommadeoptical module via a collimator and gimbal mount.The collimated laser light is directed into a custom-madeholographic optical element (Ralcon Development Lab)at an angle such that it is diffracted toward a lens focusingthe light into a SMA-connectorized endoscopy probe fiber(200- to 600-μm polymer-clad silica fiber, 0.22-0.48numerical aperture, with Tefzel jacket) that is flat-cut andpolished flush with the jacket to make it compatiblewith most endoscope channels. The probe fiber servesboth as an excitation fiber and as a scattered light collectionfiber, directing the back-scattered light towardthe optical module where it is collimated and passedthrough the holographic optical element. The considerableRayleigh scattered light (light that has not beenwavelength shifted via the Raman effect) from the tissueis diffracted out of the collimated beam by the holographicoptical element, whereas the Raman-shifted light (andtissue fluorescence, etc.) is selectively passed throughthe holographic optical element to another lens, which
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