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Optics Letters

Lamp-pumped thallium atomic line filter at 535046 nm

Bernhard P Oehry, Walter Schupita, Gottfried Magerl

Published Oct 15, 1991• 12 citations
Publisher

Abstract

We present a new atomic line filter concept for the detection of frequency-doubled Nd:BEL laser radiation. Advantage is taken of the thallium 6(2)P(3/2) metastable energy level whose large lifetime can be preserved even in small vapor cells. The filter is pumped intermittently by a low-power spectral lamp and thereby combines the benefits of active and passive operation. Analysis of a proposed final design shows that simple engineering solutions exist, and excellent filter properties can be deduced. We have experimentally demonstrated the new operating principle in a preliminary setup.

DOI
10.1364/ol.16.001620

Related papers

Experimental evaluation of an atomic line filter for spaceborne application

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Optics Letters•Apr 1, 1990•11 citations
We present a new atomic line filter concept for the detection of frequency-doubled Nd:BEL laser radiation. Advantage is taken of the thallium 6(2)P(3/2) metastable energy level whose large lifetime can be preserved even in small vapor cells. The filter is pumped intermittently by a low-power spectral lamp and thereby combines the benefits of active and passive operation. Analysis of a proposed final design shows that simple engineering solutions exist, and excellent filter properties can be deduced. We have experimentally demonstrated the new operating principle in a preliminary setup.
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.
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.
We report a simple theoretical model for the calculation of the dependence of filter quantum efficiency versus laser pump power in an atomic Rb vapor laser-excited optical filter. We present the calculations for a 532.4-nm Rb filter that can be used to detect the practical and important frequency-doubled Nd:YAG laser. The results of these calculations show that the filter's quantum efficiency is relatively insensitive to the laser pump power. The laser powers required to pump the filter range from 3.6 to 226 mW per square centimeter of filter aperture.
The major efforts of this project were: (1) to reassess the technical merits of a Tantalum atomic line filter (ALF) employing a low vapor density T1C1 and (2) to measure the excited state cesium trapping lifetimes and to derive the self quenching cross sections of excited state cesium atoms. These two separate efforts address alternative approaches to the implementation of an ALF based on metastable T1 atoms, T1 sub m, whose absorption wavelength (535 nm) matches the frequency doubled Nd:Bel laser. The first approach uses photodissociation to produce T1 sub m directly from T1C1. The second approach involves resonantly pumping the Cs in a T1-Cs mixture and collisionally transferring energy to the T1 to sustain the required density of T1 sub m.
We report the detection of frequéncy-doubled Q-switched Nd:YAG laser radiation at 532.24 nm by an active rubidium atomic resonance filter. The Rb 5p level was populated by using a diode laser operating at 795 nm. The 532-nm laser excited atoms to the 10s level; these decay through p levels to the ground state. Signals were observed at 420/422 nm and 359 nm, corresponding to fluorescence from states 6p and 7p. Fluorescence noise was observed only on the 420/422-nm transition; the 359-nm signal had no detectable noise.