We propose a non-standard spectroscopic technique that uses a feedback control of the input probe field parameters to significantly increase the contrast and quality factor of the atomic resonances. In particular, to apply this technique for the dark resonances we sustain the fluorescence intensity at a fixed constant level while taking the spectra process. Our method, unlike the conventional spectroscopy, does not require an optically dense medium. Theoretical analysis has been experimentally confirmed in spectroscopy of atomic rubidium vapor in which a considerable increase (one-two order) of the resonance amplitude and a 3-fold decrease of the width have been observed in optically thin medium. As a result, the quality factor of the dark resonance is increased by two orders of magnitude and its contrast reaches a record level of 260%. Different schemes, including magneto-optical Hanle spectroscopy and Doppler-free spectroscopy have also showed a performance enhancement by using the proposed technique.PACS numbers: 07.55. Ge, 32.30.Dx, 32.70.Jz Over time a spectroscopy has established a certain requirement to take a medium's response as a function of frequency of the probing field while the rest of the input parameters (intensity, polarization, spatial distribution, etc.) are kept at a constant level. Usually in this case the registered signals are either the absorption or the fluorescence spectra. Instead, we suggest to hold the medium response at a constant level (during the frequency scanning) by manipulation of the input probing field via electronic feedback control. In this case the changes of the governed input parameters imitate the medium's spectrum. To test our conception we have applied it to a well-known phenomenon -the coherent population trapping (CPT) [1][2][3][4].The main feature of the CPT consists in the existence of so-called dark state |dark , which is a coherent superposition state and nullifies an atomic-light interaction operatorV:V|dark = 0. In the dark state the atoms neither absorb nor emit a light. For the modern laser metrology the importance of CPT lies in the development of miniature (including chip-scale) atomic clocks [5-10] and magnetometers [11][12][13][14][15][16]. These devices are based on a two-photon resonance (for rubidium or cesium atoms, above all) formed in a bichromatic laser field, in which the frequency difference of the spectral components (ω 1 − ω 2 ) is varied near the hyper-fine splitting ∆. For such spectroscopy the existence of a pure coherent state |dark , which is sensitive to the two-photon detuning δ R =(ω 1 − ω 2 − ∆), leads to a significant increase of the contrast and quality factor (amplitude-to-width ratio) of the CPT resonance in combination with a decrease of the its light shift. Namely it explains why for alkali atoms the D 1 line is much preferable in comparison with the D 2 line, for which the pure dark state is absent in the cases of Doppler and/or collisional broadening of optical line [17,18]. Pursuing a higher resonance contrast, the new po...
Analysis of four types 4×288 designed and manufactured readouts is presented. All the readouts have the direct injection input circuit with the circuits incorporated that allows testing procedure of readouts without the photodiodes attached to readout circuits. TDI registers have three delay elements between neighbouring inputs. Some characteristics of 4×288 FPAs with mercury-cadmium-telluride (MCT) arrays are presented too. Analysis have shown that in spite of different constructions of four readout types, different numbers of outputs and external service, rather similar parameters of FPAs have been obtained. Detectivity values measured for all 4×288 FPAs at operation temperature T ≈ 78 K with skimming mode included and background temperature Tb ≈295 K were in the range D*λ ≅ (1.2−1.7)×1011 cmHz1/2/W.
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