Raman spectroscopy can be used extensively, from handheld substance identification systems to in-vivo cancer detection. The ability to quickly and non-invasively identify compounds based on intrinsic vibrational signatures has seen Raman applications skyrocket in recent years - many using fiber optic probes. This paper describes the modeling, deposition, lithographic patterning, and testing of filters directly deposited onto the distal tip of a fiber bundle. These spectrally sharp bandpass and long pass filters allow for the detection of Raman scattering down to about 200 cm-1 . Blocking of laser radiation above OD6 is enabled by coating both the distal and proximal tips.
Laser based applications including optical communications, LIDAR and Raman spectroscopy benefit from ultra-narrow (< 1.0 nm) bandpass and high edge slope dichroic optical filters by rejecting off-band ambient and scattered light. However, applications for these filters are limited by shifts in wavelength due to temperature and angle of incidence, system f-number, doppler shift and pointing error of the gimbal as well as the stability of the source. Passive design techniques such as athermalization, use of high refractive index materials and widening the passband are compared with active tuning options. Adding thermal or tilt tuning can expand the operational range of the filter and mitigate the compromise to signal to noise which follows from widening the passband.
Narrow bandwidth linear variable filters (NB-LVF) bring hyperspectral imaging to a wide range of applications in a compact, low weight, rigid structure. The center wavelengths of the narrow bandpass of a linear variable filter changes smoothly in one dimension and are constant in the orthogonal dimension along the surface of the filter. The filter, which is the size of the camera’s detector, is placed directly ahead of the detector and successive frames are acquired as the camera skews or as the camera platform moves across a scene. The full width, half maximum bandwidth of the filter used is 0.8% of the center wavelength and the spectral range is 400 to 900 nm with a wavelength gradient of 50 nm/mm. Examples using the LVF camera for emission spectroscopy, absorption spectroscopy, machine vision, and industrial process control and hyperspectral imaging are presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.