Diffused reflectance infrared spectroscopy is well known as a compact, low-cost, and efficient handheld spectrometers. One of the spectrometer’s most important optical parameters is the effective collected spot profile from diffuse reflection samples not the simple illumination spot which determines the analyzed sample portion defining the spatial resolution. In this work, we present a novel method for characterizing the spot size based on the Knife-Edge technique. A sharp high scattering material such as PTFE is displaced into the spectrometer optical interface on a 1-dimensional moving stage while capturing the power at each step. Then by differentiating this cumulative power, the intensity spot profile is obtained and fitted to a Gaussian profile where the spot size is defined as the diameter that contains 90% of the reflected power. MEMS FT-IR spectrometers with different spot sizes measured as a demonstration of the technique. Moreover, this method quantifies different other parameters such as Goodness of Fit, spot lateral shift in addition to spot shape wavelength dependence that may occurs due to any non-ideality in the spectrometer system.
In this work we present a scheme to enhance the spectral resolution of the MEMS FTIR spectrometer by cascading it with a reflection-type Fabry-Perot (FP) cavity. In this scheme, we use the different FP longitudinal modes in the reflection response within the FTIR spectrometer range simultaneously to scan the entire spectrum of the measured material, while at the same time the FTIR discriminates between the contributions of those different modes. This discrimination can only be made successfully given that the resolution of the FTIR engine is smaller than the free spectral range (FSR) of the reflection FP. A DSP algorithm is developed to decode the correct spectrum of the measured material using the presented spectrometer. The suggested architecture is implemented experimentally using a reflection FP cavity, consisting of a micromirror and a Bragg coated multimode optical fiber, with a scanning MEMS Michelson interferometer having a resolution of 16 nm at 1550 nm. A 50/50 optical splitter is used to cascade the reflection FP cavity and the MEMS Michelson interferometer. The system was used to resolve two laser lines at 1548 nm and 1554 nm achieving a resolution of 6 nm at 1550 nm leading to about 2.6 times enhancement in spectral resolution. The system was also used to measure the absorption lines of a references material in the wavelength range of 1450 nm to 1750 nm. The result was compared to the measurement of a bench top spectrometer with a good agreement.
In this work we report on combining MEMS Michelson interferometer core engine cascaded with a low finesse Fabry-Perot (FP) tunable filter to enhance the spectral resolution over a wide spectral range. In this scheme, the different FP longitudinal modes within the FTIR spectrometer range are utilized simultaneously to scan the spectrum of the measured material by tuning the filter, while the FTIR engine discriminates between the contributions of the different FP modes; given that the spectral resolution of the FTIR engine is smaller than the FSR of the FP. The presented scheme is implemented experimentally using a FP cavity which is finely tuned using piezo actuator, with a scanning MEMS Michelson interferometer achieving a resolution of 16 nm at 1550 nm. The system is used to resolve two laser lines at 1548 nm and 1552 nm achieving a resolution of 4 nm at 1550 nm leading to four times enhancement. We also measured the absorption lines of a references material in the wavelength range of 1450 nm to 1750 nm and compared it to the measurement of a bench top spectrometer and the two results are in close agreement
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.