Biomedical subjects

Scott T Sanders

Publications and source records attributed to Scott T Sanders.

5 recordsLinked to original sources

PubMed2006

Continuous-wave frequency comb Fourier transform source based on a high-dispersion cavity.

A dispersive grating compressor was included in a fiber ring laser to generate an unequally spaced frequency comb spanning approximately 1549-1552 nm. Beating of nearby modes in the comb naturally assigns unique amplitude modulation frequencies to each spectral component emitted. The source contains no moving parts. The single-mode fiber-coupled output is directed through hydrogen cyanide gas and detected by a photodiode. A Fourier transform of a 1 ms record yields a spectrum that agrees with results from a grating spectrometer at 0.06 nm resolution. By engineering stable, broadband combs, the technique could result in a universal and simple approach for spectroscopy at almost arbitrary measurement speeds and spectral resolutions limited only by Fourier principles.

Journal Article↗

PubMed2006

Assessment of multiphoton absorption in inert gases for the measurement of gas temperatures.

A spatially resolved optical technique to measure gas temperature was assessed. The technique relies on multiphoton absorption in inert gases. In contrast to laser-induced fluorescence, absorption is insensitive to collisional deactivation, and, in contrast to one-photon absorption, multiphoton absorption only occurs around the focus point of a typical laser beam. Multiphoton absorption features both the merits of being insensitive to quenching and of being a spatially resolved technique. In a case study we assessed two-photon absorption in xenon upon exciting the 5p6 1S0-->5p56p[5/2]2 transition in xenon at a wavelength of 256 nm. The amount of light absorbed by xenon is related to the number density of the gas, and if the gas pressure is known then the gas temperature can be inferred from the number density. Two-photon absorbance was measured as a function of xenon number density and was used to validate a theoretical model of the absorption process. We discuss the circumnavigation of experimental challenges in applying this technique and analyze its precision in terms of the inferred gas temperature.

Absorption↗

PubMed2005

Optical design in beam steering environments with emphasis on laser transmission measurements.

Optical sensors applied to practical devices often encounter beam steering: the wander and/or diffusion of laser light. Here we provide a framework for minimizing the sensitivity of transmission-based sensors to beam steering without quantitative prediction of the severity of the beam-steering field. Typical goals are increased transmission and/or minimized fluctuations in transmission; such features can improve optical sensor performance (e.g., improved signal-to-noise ratio, response time, or spectral resolution). In our framework, we introduce a parameter for characterizing beam-steering severity. We then compare two approaches for absorption spectroscopy and show that the preferred approach depends on the total spectral range monitored, the spectral resolution desired, and the severity of the beam steering.

Journal Article↗

PubMed2005

Differential absorption sensor applied for liquid oxygen measurements.

Differential laser absorption was investigated for its merit in liquid oxygen (LOX) sensing. Whereas previous researchers have used differential absorption to detect trace concentrations of a substance, we use differential absorption to monitor small changes in large amounts of a substance. Two lasers of different wavelengths were intensity modulated 180 deg out of phase from each other and multiplexed into a single beam. After probing the LOX, the total transmitted signal was demodulated by a lock-in amplifier. Our experiment simulated rapid changes in LOX number density by varying the length of an approximately 73 mm path through pure LOX. In this experiment, we demonstrated the ability to monitor LOX number density with an uncertainty of approximately 1% with a time constant of 3 micros. The uncertainty could be halved by doubling the path length, and this improvement could be repeated as long as the relative intensity noise of the lasers is the dominating factor. We discuss the benefits of differential absorption for problems requiring an extended dynamic range.

Journal Article↗

PubMed2005

Rapid wavelength scans over one octave and application to laser-induced fluorescence.

Rapid excitation scans of laser-induced fluorescence (LIF) have been demonstrated. Broadband light was generated in a photonic crystal fiber and transmitted through a long fiber. Due to group-velocity dispersion in the long fiber, a wavelength scan emerged from the fiber in time. The wavelength was swept over approximately one octave in approximately 150 ns. The generated light was used to excite LD 700 Perchlorate diluted in methanol. The LIF excitation scan had a spectral resolution of approximately 15 nm, and the integrated fluorescence spectrum was found to be within 7% of the integrated absorption spectrum of the dye molecule. The method presented makes possible spatially and spectrally resolved LIF excitation scans with scanning speeds up to the limits set by the excited-state lifetime of the dye molecule.

Journal Article↗