Richard F. Majkowski

Tunable diode laser spectroscopy for isotope analysis-detection of isotopic carbon monoxide in exhaled breath

A high resolution tunable infrared diode laser spectroscopy system was developed for isotope analysis with sensitivity at parts per billion levels. Such a system is ideally suited for detection and measurement of minute amounts of infrared active compounds present in a huge noninfrared active background such as air. The operation and capabilities of the system were demonstrated by measuring physiological levels of isotopic carbon monoxide, /sup 12/C/sup 16/O and /sup 13/C/sup 16/O, naturally present in exhaled human breath with essentially no sample preparation. The simplicity in obtaining such data suggests that fundamental physiological information may be derived from noninvasive measurements. This makes the system potentially useful for many biomedical applications.<<ETX>>

High resolution infrared diode laser spectroscopy for isotope analysis—Measurement of isotopic carbon monoxide

A tunable infrared diode laser spectroscopic system for stable isotope analysis has been developed. The system uses (1) a tunable single mode PbTe/PbEuSeTe diode laser and (2) a sample cell with dual path length matched to the expected order of relative isotopic spectral intensities. Because of the unique features of such a system, isotopic molecules with similar mass and vastly different concentrations can readily be detected and measured. The principle and operation of the system are described, and the relative abundance of isotopic carbon monoxide 12C16O, 12C17O, 12C18O has been measured for the first time by a tunable diode laser system.

SPECTROSCOPIC MEASUREMENTS OF TEMPERATURES AND DENSITIES IN A CESIUM PLASMA

The ion, electron and atom number densities, and electron temperatures of a cesium plasma generated in a diode have been measured by spectroscopic techniques. The theoretical bases for these techniques are outlined. The errors involved in applying these theories to heavy atom collision‐dominated plasmas are discussed. Working equations for the electron, ion and atom temperatures, and number densities are developed. Among the working equations developed and applied are those for the determination of the electron number density from the continuum intensity and Stark broadening. Temperatures in the cesium plasma were 0.7 ev with ion and electron number densities of the order of 1015 cm−3. The agreement of cesium pressure computed from the spectroscopically determined temperatures and number densities and that from vapor pressure curves strongly suggest the existence of thermal equilibrium. The agreement in the values of electron number densities determined from continuum intensity and Stark broadening measur...

Stripe geometry lead‐telluride diode lasers grown by molecular beam epitaxy

Lead‐telluride homojunction diode lasers suitable for ultrahigh resolution spectroscopy have been fabricated using molecular‐beam epitaxial (MBE) growth and a mesa stripe geometry. A low‐MBE substrate growth temperature of 260 °C was used to minimize interdiffusion during growth. These lasers operate up to 115 K cw with emission in the 6.5–5.0‐μm wavelength range. The threshold current density follows the relation J=J0 exp(T/T0) up to 100 K, with J0=110 A/cm2 and T0=26.0 K. Thermal resistance effects cause a departure from this relationship at higher temperatures. The current‐voltage relationship as a function of temperature indicates that tunneling currents contribute significantly to the threshold current density. Single‐fundamental mode emission is obtained from 20‐μm‐wide mesa stripes at high temperature, whereas a higher order mode is observed with 35‐μm‐wide stripes. Analysis of the near and far field patterns indicates that the lasing mode is index guided at high temperatures, and gain guided at lo...

Holographic System for Automatic Surface Mapping

The surfaces of large (approximately 1-m) diffusely reflecting objects can be mapped by automatic following of the holographic real image of the object. Large aperture, low f number holograms give the shallow depth of focus required for this method. The ability to apply the technique to situations requiring a pulsed laser is demonstrated. Unity magnification real images from holograms made with a Q switched ruby laser have a measured metric fidelity of at least one part in 10(4) over an object field of 60 deg. A sinusoidal optical interference pattern projected onto the object when the hologram is taken provides the type of contrast pattern necessary for unambiguous determination of the location of the focused image surface and facilitates automatic focus detection. The image is scanned by an image dissector that is moved about the image by a 3-axis slide system. A computer analyzes the video signals, directs the machine motions to follow the image, and provides an output of surface dimensions in digital form. A prototype machine using cw helium-neon lasers for object illumination and image reconstruction is described and performance data presented.

Time-Resolved Measurement of Vehicle Sulfate and Methane Emissions with Tunable Diode lasers

A new analytical method, absorption of tunable diode laser radiation, can detect small concentrations of gases with fast response. This technique has been applied to the detection of vehicle sulfate emissions in the form of sulfuric acid (H2SO4) vapor. Our laser system has a response time of 2.4 s. This allowed tracking the sulfate emissions of a vehicle during a Highway Fuel Economy Test. The data suggests that catalyst temperature is the major parameter controlling sulfate emissions and that storage and release of sulfur occurs at low and high catalyst temperatures, respectively. The same method detected methane during both the Highway Fuel Economy Test and the Federal Test Procedure. It identified the conditions, and corresponding concentrations, for high methane emissions.

Infrared absorption coefficient of H 2 SO 4 vapor from 1190 to 1260 cm −1

The infrared absorption coefficient of H2SO4 vapor has been measured for the first time. The vapor was obtained from liquid acid held at the azeotrope. The temperature dependence of the absorption confirmed that the azeotrope concentration was accurate to better than 1%. The P, Q, and R branches of the measured band cover a spectral range of 1190 to 1260 cm−1. The peak absorption coefficient of 4.16 ±0.15 atm−1 cm−1 occurred at 1222 cm−1 within the Q branch, with an integrated absorption coefficient of 120 atm−1cm−2 over the entire band. Within the resolution of the experiment, 0.5 cm−1, no fine structure was observed on this band.