Record performances were demonstrated in terms of output power (>9 mW) and conversion efficiency (12%) for a 250 GHz Heterostructure Barrier Varactor tripler. These excellent performances can be explained by the highly non linear capacitance-voltage characteristics of InGaAs/InAlAs/AlAs diodes having a zero-bias capacitance of 1fF/μm2, a capacitance ratio of 6:1 and a breakdown voltage of 12 V.
A small number N (105≥N≥1) of sodium atoms in an atomic beam are prepared by pulsed laser excitation in a nS Rydberg level (n≂30) while transversing a millimeter wave Fabry–Perot cavity tuned to a transition connecting the nS state to a nearby n′P level. The atoms absorb the radiation in the cavity (nS→nP upward transition), or amplify it in a maser process [nS→(n−1)P, nS→(n−2)P... downward transition]. Due to the huge size of the electric dipole matrix element between nearby Rydberg levels, the system is extremely sensitive to the millimeter wave radiation field (enhanced by the tuned cavity) in both absorption and emission processes. Simple numerical expressions are given. The experiments demonstrate that the system can be used as an absolute power meter, an ultrasensitive millimeter photon counter, an absolute quantum thermometer, and a transient millimeter-wave amplifier.
A new technique is presented for measuring the spectral broadening of light that has been multiply scattered from scatterers in motion. In our method the scattered light is detected by a heterodyne receiver that uses a CCD as a multipixel detector. We obtain the frequency spectrum of the scattered light by sweeping the heterodyne local oscillator frequency. Our detection scheme combines a high optical etendue (product of the surface by the detection solid angle) with an optimal detection of the scattered photons (shot noise). Using this technique, we measure, in vivo, the frequency spectrum of the light scattered through the breast of a female volunteer.
We present various experiments involving atoms interacting with resonant microwave electromagnetic fields inside a cavity, allowing to check different features of the theory presented in the previous paper. We first describe experiments about superradiant emission by states in the cavity, also called transient atoms maser; the evolution of the system is detected either on the populations by selective field ionization technique or on the microwave field itself by heterodyne detection. Very low thresholds, down to 100 atoms, for the maser emission have been observed. We then describe various aspects of collective absorption of radiation by very excited atoms including the observation of Rabi nutation in a small applied resonant field, the study of the quantum efficiency of this set-up considered as a microwave photon counter, and finally the unexpected characteristics of the blackbody radiation absorption in the cavity. In this second paper, we present various experiments on states interacting with resonant millimetric electromagnetic waves inside a cavity. These experiments show various interesting physical effects calculated in the previous paper and provide a test for the theoretical models. In a first paragraph, we will describe the experimental techniques which are common to all the experiments that will be presented afterwards. We will devote the second paragraph to an experimental study of the different characteristics of the collective atom transient emission in the cavity (the Rydberg atom maser). In the last paragraph, we will describe several experiments involving the absorption of radiation by very excited states in the cavity and showing the collective behaviour of the atoms in this absorption process. 1. Experimental techniques 1.1. P£ep_ar.ation_of_the_p_hy_sicaX_sy_stem In order to prepare the physical system which has been theoretically studied in the previous paper, i.e. a set of 2-level atoms in resonant interaction with an electromagnetic mode inside a cavity, we use the experimental set-up which Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982221
A multiple frequency heterodyne imaging system has been established and is now being used to study a range of biological and material samples in the submillimeter wave frequency regime. Advantages of this imaging system include signal-to-noise >80 dB from 200 to 700 GHz, true magnitude and phase, simple frequency shifting, dual simultaneous frequency measurements, and transportable transmit and receive heads. This paper describes the test system and presents some examples of its use for biological and space science applications.
We analyze in this paper various aspects of the interaction of Rydberg atoms with resonant electromagnetic cavity. We show that an ensemble of Rydberg atoms coupled to a single field mode at a finite temperature behaves as a single guantum object exhibiting features of Bose-Einstein statistics and Brownian motion. We analyze the transient amplification of the blackbody field by a Rydberg sample and study the change of the photon emission statistics as a function of time. We also show that an isolated Rydberg atom in a cavity undergoes either an oscillating or a damped evolution according to the respective valuesof the atom to field coupling and cavity damping times and we analyze this effect in term of a modification of the vacuum field modes surrounding the atom. Experiments to check these effects are under progress and will be described in next paper.
By high-resolution double-resonance spectroscopy experiments in the millimeter-wavelength domain, we have determined precise values of the quantum defects in the s and p Rydberg levels of $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ (principal quantum number n ranging from 18 to 40). A detailed comparison of the $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ data has yielded the value of the specific isotopic shift in the np series, which is the first evidence to our knowledge of an exchange effect between a tightly bound core electron and a very weakly bound Rydberg electron in an alkali-metal atom.
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