The existence of cross-over resonances makes saturated-absorption spectra very complicated when external magnetic field B is applied. It is demonstrated for the first time that the use of micrometric-thin cells (MTC, $Lapprox40,mu$m) allows applicati
on of SA for quantitative studies of frequency splittings and shifts of the Rb atomic transitions in a wide range of external magnetic fields, from 0.2 up to 6 kG (20-600 mT). We compare the SA spectra obtained with the MTC with those obtained with other techniques, and present applications for optical magnetometry with micrometer spatial resolution and a broadly tunable optical frequency reference.
We report on the characterization of candidate light sensors for use in the next-generation Imaging Atmospheric Cherenkov Telescope project called Cherenkov Telescope Array, a major astro-particle physics project of about 100 telescopes that is curre
ntly in the prototyping phase. Our goal is to develop with the manufacturers the best possible light sensors (highest photon detection efficiency, lowest crosstalk and afterpulsing). The cameras of those telescopes will be based on classical super-bi-alkali Photomultiplier tubes but also Silicon Photomultipliers are candidate light sensors. A full characterisation of selected sensors was done. We are working in close contact with several manufacturers, giving them feedback and suggesting improvements.
Contemporary imaging air Cherenkov telescopes (IACT) for ground-based very high energy (VHE) gamma ray astronomy have prime focus optical design. Typically these telescopes have a 2-4 deg wide field of view (FoV). They use f/0.7-f/1.2 optics and prov
ide 3-10 arcmin resolution in the FoV. Generally, a well designed telescope that includes more than one optical element will offer some advantages not available in prime focus designs, such as a wider FoV, a more compact size, a higher and more homogeneous resolution and a lower degree of isochronous distortion of light rays focused onto the focal plane. Also, they allow monitoring the gamma ray activity in a sizeable portion of the sky in a single observation. This would allow one to perform a sensitive all-sky survey in a relative short time. We present an f/0.8 15 deg wide FoV telescope design, which provides a high and near uniform resolution and low isochronous distortion across the entire FoV.
The SiPM is a novel solid state photodetector which can be operated in the single photon counting mode. It has excellent features, such as high quantum efficiency, good charge resolution, fast response, very compact size, high gain of 106, very low p
ower consumption, immunity to the magnetic field and low bias voltage (30-70V). Drawbacks of this device currently are a large dark current, crosstalk between micropixels and relatively low sensitivity to UV and blue light. In the last few years, we have developed large size SiPMs (9 mm^2 and 25 mm^2) for applications in the imaging atmospheric Cherenkov telescopes, MAGIC and CTA, and in the space-borne fluorescence telescope EUSO. The current status of the SiPM development by MPI and MEPhI will be presented.
