Christopher F. Klein

Saturated optical nonresonant emission spectroscopy (SONRES) for atomic detection

We have demonstrated the extremely small detection limits that can be achieved in a high‐pressure environment by the combination of saturated absorption and nonresonance emission spectroscopy. The method of SONRES exploits efficient energy transfer between excited atomic states at high pressures and intense optical fields available from tunable lasers. An estimated 104 atoms/cm3 of sodium were monitored in a flame; the corresponding atomic concentration was 1 part in 1015. A detection limit of ∼10 atoms/cm3 was recorded for sodium in argon. The ultimate detection limit for this method is ∼10−4 atoms.

Infrared detection by an atomic vapor quantum counter

An efficient technique for the detection of nartowband infrared radiation by up-conversion in an optically saturated atomic vapor is described. The strong transition cross sections provided by the resonance interactions combined with the narrow Doppler spectral response profile contribute to the potential to approach quantum-noise-limited performance. Experimental results confirm the model of the detection process for sodium transitions at 1.48, 2.34, and 3.42 μ. The predicted ultimate noise equivalent power (NEP) of this device is less than 10-17W/Hz1/2in the 1.5-5-\mu spectral region.

Single-atom detection by SONRES

The new method of atomic fluorescence detection, called saturated optical nonresonant emission spectroscopy (SONRES), has been modeled for a three-level atom, and experiments on sodium have been conducted that support the model. A rate equation analysis yielded expressions for excited-state atomic populations and saturation intensity. The detection of sodium in buffer gases that promote collisional transfer of excitation between 32P 1/2 → 32p 3/2 both without quenching the fluorescence emission and with quenching was considered. Experimental results are presented for sodium in argon. At -25°C, approximately 180 atoms/cm3were monitored with a S/N of ∼ 15 representing detection at the level of one part in 1017. The signal at this temperature was generated by less than a single atom in the laser beam.

Methodology for rapid infrared multispectral electro-optical imaging system performance analysis and synthesis

An analysis methodology and corresponding analytical tools for rapid top-down design of multi-spectral imaging systems is presented. Beginning with top- level customer-dictated system performance requirements and constraints, the critical system and component parameters in the electro-optical image chain are derived, performance analyzed, and iterated until a preliminary design that meets customer requirements is generated. System parameters and components composing the image chain for staring, scanning, pushbroom, and time-delay and integrate systems include: aperture, focal length, field of view, cold shield requirements, image plane dimensions, pixel dimensions, pixel pitch and fill factor, detection quantum efficiency, optical filter requirements, image plane dimensions, pixel dimensions, pixel pitch and fill factor, detection quantum efficiency, optical filter requirements, and temporal sampling parameters. The performance analysis is accomplished by calculating the imaging systems optical response (to a scene radiance), total noise, and imaging resolution. The noise components include photon noise due to signal, scene and atmospheric background, cold shield, out-of-band optical filter leakage and electronic noise. System resolution is simulated through cascaded optical transfer functions (OTFs) and includes effects due to atmosphere, optics, image sampling, and system motion.

Stimulated emission cross section at 1.061 μm in Nd:YAG

The stimulated emission cross section of the 1.061‐μm transition (R1—Y1) in Nd: YAG has been measured and is (5.1 ± 0.5) × 10−19 cm2 on the same scale that assigns the value 8.8 × 10−19 cm2 to the 1.064‐μm line. The thresholds of the 1.061‐ and 1.064‐μm lines have been determined over the temperature range of 100–300 °K and are equal at 229 °K.

Two optical methods for vehicle tagging

Optical tagging methods have the advantage that they cannot be detected by a suspicious criminal or terrorist using a radio frequency (RF) sensitive device to scan his vehicle for the presence of an RF emitting tag. We will describe two optical tagging methods in which the presence of the tagging marks can be visually discovered only by very close observation. On the other hand, the tags can be readily recognized by a surveillance team through the use of infrared imagers, either in the longwave infrared (LWIR) or in the near infrared (NIR). The first approach uses a clear coating that has a higher thermal emissivity than the glass window to which it is applied. This coating can be viewed with a thermal imager that operates in the LWIR, with the tags appearing as bright marks on a dark background. The second method uses an NIR laser illuminator and also quarter-wave thick layers applied to the license plate of a vehicle. When viewed with a polarization-sensitive imager that operates in the NIR, these quarter-wave tags appear as bright marks on a dark background. We will show sample images of both of these optical tags, as viewed in the LWIR and NIR regions, respectively.

Stark tuning of the atomic vapor quantum counter

The atomic vapor quantum counter (AVQC) offers the potential for efficient upconversion of narrow-band IR radiation. This paper explores wavelength tuning of the AVQC by the application of an electric field (Stark effect). Model calculations indicate the Stark effect in combination with the proper selection of IR transitions in the atomic vapor can yield continuous tuning across the entire 2-20 \mu m spectral region. Experimental results near 10 μm have demonstrated over 23 cm-1tuning on a single potassium vapor transition. Thirteen CO 2 laser wavelengths were scanned in this fashion.

Novel dichroic beam separator for frequency-doubled lasers.

A novel glass rhomb has been demonstrated for separating the residual fundamental beam from the harmonic beam in a frequency-doubled or frequency-tripled laser. This device features simple fabrication, damage resistance of uncoated glass, essentially loss-free transmittance for the harmonic beam, high (> 95%) rejection of the fundamental, mechanical and thermal stability, and high optical quality.

Single-Atom Detection By One-Photon And Two-Photon Sonres

Saturated Optical Nonresonance Emission Spectroscopy (SONRES) has been applied to metallic vapor detection. Using one-photon cw excitation less than 0. 2 atoms of sodium have been detected in the laser interaction volume with an ambient pressure environment. The method has been applied to the ultraviolet transitions of nickel and platinum using pulsed excitation sources, achieving detection limits less than 100 atoms in the detection volume for an ambient pressure high temperature environment. Resonance enhanced two-photon excitation has also been investigated for atomic detection applications. Experiments demonstrate that the two-photon method can be expected to achieve ultimate detection limits of 10-3 atoms in the laser interaction volume, approaching the theoretical limit of the one-photon SONRES method. The two-photon method provides optimum performance at low pressure and furnishes the sub-Doppler resolution required for highly selective isotope analysis.