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Optics Letters

Proposed Fraunhofer-wavelength atomic filter at 5349 nm

Jerry A. Gelbwachs

Published Oct 15, 1990• 7 citations
Publisher

Abstract

A new atomic filter is proposed. It operates at 534.9 nm. The new filter offers two important advantages for openchannel laser communications. First, its wavelength matches the output of the frequency-doubled Nd:BEL laser. Second, the filter overlays a solar Fraunhofer line, thereby offering intrinsic sunlight suppression. Ultranarrowband optical filtering takes place within the singlet manifold of neutral-calcium vapor. Excellent filter properties are deduced from spectroscopic examination of the atomic system. A novel feature of the new filter is the potential for greater-than-unity internal photon conversion.

DOI
10.1364/ol.15.001165

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Atomic resonance filters

Jerry A. Gelbwachs

The atomic resonance filter (ARF) is an ultranarrowband (Q approximately 10/sup 5/-10/sup 6/), large-acceptance-angle, isotropic optical filter. These features make the device ideally suited for applications in which weak laser signals are detected against a continuum background. The filter properties arise from the physical processes of absorption, emission, and internal energy conversion in atomic vapors. The characteristics of the ARF are described and the underlying physics that governs the operation is discussed. Representative examples of passive, active, and IR filters are presented. A metastable ARF that offers improved solar background-limited performance by filtering signals at Fraunhofer wavelengths is described.>

IEEE Journal of Quantum Electronics•Jul 1, 1988•88 citations
A new atomic filter is proposed. It operates at 534.9 nm. The new filter offers two important advantages for openchannel laser communications. First, its wavelength matches the output of the frequency-doubled Nd:BEL laser. Second, the filter overlays a solar Fraunhofer line, thereby offering intrinsic sunlight suppression. Ultranarrowband optical filtering takes place within the singlet manifold of neutral-calcium vapor. Excellent filter properties are deduced from spectroscopic examination of the atomic system. A novel feature of the new filter is the potential for greater-than-unity internal photon conversion.
A demonstration of the first magnetooptic atomic filter that overlays a strong solar Fraunhofer line is reported. Compared with alkali magnetooptic filters, this filter enjoys a large reduction in solar interference and a significant decrease in the number of noise passbands. The filter utilizes the strong Ca(4p/sup 1/P/sub 1/-4s/sup 1/S/sub 0/) transition at 422.7 nm. Under the weak magnetic field experimental conditions, a maximum transmission efficiency of 55% and a symmetrical double-peaked transmission spectrum with 1.5 GHz wide passbands were observed. The filter's frequency response was measured with a laser intensity modulation technique. No falloff was observed at 176 MHz, the highest frequency available with the apparatus. Calculations indicate that further improvements in filter performance can be achieved by optimizing the magnetic field and the cell temperature.>
Atomic line filters take advantage of the sharp spectral features offered by electronic transitions in free atoms. The basic idea is to convert a narrow atomic absorption profile into an equally narrow optical transmission filter by detecting the fluorescence radiation that is emitted after a photon has been absorbed. We developed the metastable thallium atomic line filter from the basic physical idea to a laboratory prototype in order to evaluate the usefulness of the technology for satellite borne backscatter LIDARs. Atomic thallium provides for an unsurpassed combination of features for this purpose. The input wavelength of the filter is 535 nm, which matches the frequency doubled Nd:BEL laser. The filter is an active device, it upconverts the 535 nm input into 378 nm output that is detected by a PMT. The experimental results were as expected concerning the characteristics directly related to atomic properties, i.e. the filter has only 10 ns response time, its optical bandwidth is 0.004 nm, and its acceptance angle is only limited by the device geometry. An optimized setup, with the size constraints of a space-borne system, displays a total quantum efficiency of 2%, i.e. from input photons to detected output photons. This constitutes a remarkable and unsurpassed value for atomic line filters but is too low for the application in mind. (A ground-based, scaled-up version of our prototype would reach about 10% quantum efficiency). In addition, the 500 degree(s)C operating temperature of the vapor cell requires sophisticated thermal layout and thermal shielding, which means a lot of added mass and volume. In summary, we found that atomic line filters can be built that offer characteristics not found with other technologies, but their applicability for space borne systems is questionable.
The atomic resonance filter (ARF) is an ultranarrowband (Q approximately 10/sup 5/-10/sup 6/), large-acceptance-angle, isotropic optical filter. These features make the device ideally suited for applications in which weak laser signals are detected against a continuum background. The filter properties arise from the physical processes of absorption, emission, and internal energy conversion in atomic vapors. The characteristics of the ARF are described and the underlying physics that governs the operation is discussed. Representative examples of passive, active, and IR filters are presented. A metastable ARF that offers improved solar background-limited performance by filtering signals at Fraunhofer wavelengths is described.>