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Di Rosa, Michael D.

Publications and source records attributed to Di Rosa, Michael D..

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Multiplexing of frequency-modulation spectroscopy by spread-spectrum codes, demonstrated in continuous-wave LIDAR

Frequency-modulation spectroscopy (FMS) is generally suited to code-division multiplexing, and we demonstrate that capacity in a form of continuous-wave LIDAR, utilizing a sharp CO 2 absorption transition at 1.6 µm in simple ranging setups. The approach retains the advantages of FMS, including coherent detection and good rejection of broad absorption backgrounds. Extensions of this multiplexed approach to the continuous, simultaneous detection of several transitions would come by transmitting an encoded combination of frequency-modulated carriers, each tuned to detect a unique absorption transition. Signal analysis at the receiver involves a simple process of de-multiplexing that, in a general application, reveals targets at various distances and the absorption-related FMS signals in between.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Computational expressions for signals in frequency-modulation spectroscopy

In this study, general expressions for the signals in frequency-modulation spectroscopy (FMS) appear in the literature but are often reduced to simple analytical equations following the assumption of a weak modulation index. This is little help to the experimentalist who wants to predict signals for modulation depths of the order of unity or greater, where strong FMS signals reside. Here, we develop general formulas for FMS signals in the case of an absorber with a Voigt line shape and then link these expressions to an example and existing numerical code for the line shape. The resulting computational recipe is easy to implement and exercised here to show where the larger FMS signals are found over the coordinates of modulation index and modulation frequency. One can also estimate from provided curves the in-phase FMS signal over a wide range of modulation parameters at either the Lorentzian-broadening or Doppler-broadening limit, or anywhere in between by interpolation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2012

Passive Heterodyne Detection Using Multiple Spatial Modes

We investigated the utility of passive heterodyne detection for the remote sensing of chemicals. We performed sensor simulations for a heterodyne receiver that operates with multiple spatial modes of radiation. We find that the heterodyne signals associated with distinct spatial modes of radiation can be detected in combination. We compare this to the well-known concept referred to as the “Siegman antenna theorem”, which is usually interpreted as limiting heterodyne receivers to a single spatial mode. We show that the heterodyne signal/noise ratio does not improve beyond the single-mode SNR. We discuss the possibility of performing imaging in the multi-mode configuration, using a multi-mirror array or an array heterodyne detector. We conclude that multiple-mode passive heterodyne sensing requires a bright source of radiation, since the combination of the modes does not boost the SNR. We discuss why passive heterodyne imaging is potentially feasible.

42 ENGINEERING↗
DOE OSTI2012

Cooling Molecules with Laser Light (Final Report)

Certain diatomic molecules are disposed to laser cooling in the way successfully applied to certain atoms and that ushered in a revolution in ultracold atomic physics, an identification first made at Los Alamos and which took root during this program. Despite their manipulation into numerous achievements, atoms are nonetheless mundane denizens of the quantum world. Molecules, on the other hand, with their internal degrees of freedom and rich dynamical interplay, provide considerably more complexity. Two main goals of this program were to demonstrate the feasibility of laser-cooling molecules to the same temperatures as laser-cooled atoms and introduce a means for collecting laser-cooled molecules into dense ensembles, a foundational start of studies and applications of ultracold matter without equivalence in atomic systems.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1993

Continuous wave dye-laser technique for simultaneous, spatially resolved measurements of temperature, pressure, and velocity of NO in an underexpanded free jet

Gas dynamic quantities within an underexpanded nitrogen free jet, seeded with 0.5 percent NO, were measured nonintrusively by using an intracavity-doubled, rapid-tuning, CW ring dye laser. The UV beam passed obliquely through the jet axis, and its frequency repetitively scanned across adjacent rotational lines in the NO gamma band near 225 nm at a rate of 4 kHz. Spatially resolved excitation scans were obtained by monitoring the induced broadband fluoresence. Modeling the Doppler-shifted excitation scans with Voigt profiles permitted simultaneous determinations of NO velocity, rotational temperature, and pressure. Zero Doppler shift was referenced to an absorption trace obtained across a static cell and recorded concurrently with the excitation scan. Typically, the measured and predicted axial distributions agreed within 10 percent. At high Mach numbers there was evidence of rotational freezing of NO.

Di Rosa, Michael D.↗