Yuriy Divin

Hilbert-transform spectroscopy with high-T/sub c/ Josephson junctions: first spectrometers and first applications

First laboratory prototypes of Hilbert-transform spectrometers have been developed. To meet the requirements of Hilbert-transform spectroscopy, high-T/sub c/ Josephson junctions with RSJ-like behavior have been fabricated on twin-free NdGaO/sub 5/ bicrystal substrates. The operation of the spectrometers has been demonstrated from 60 GHz up to 2.25 THz. The first out-of-lab application of Hilbert-transform spectrometers has been successfully demonstrated at the TESLA Test Facility linear accelerator at DESY (Hamburg). The spectra of coherent transition electromagnetic radiation from electron bunches have been measured and a bunch length of /spl sigma//sub t/=1.2 ps has been derived from these spectra. The market perspectives for Hilbert spectrometers have been estimated.

Frequency-selective incoherent detection of terahertz radiation by high-Tc Josephson junctions

The detector response of YBa2Cu3O7−x Josephson grain-boundary junctions to monochromatic radiation with the frequency f in the range from 60 GHz to 4 THz has been studied. Frequency-selective odd-symmetric resonances in the responses ΔI(V) of these junctions to radiation with different frequencies f have been observed near the voltages V=hf/2e in almost a decade of spectral range for any operating temperature in the range from 30 to 85 K. The spectral range of the selective detection has scaled with the IcRn product of the Josephson junction, reaching the range of 0.16–3.1 THz for a IcRn product of 1.5 mV. A resolving power δf/f of around 10−3 has been demonstrated in the selective detection by Josephson junctions. The high-frequency falldown of the amplitude of the selective response has been found to be proportional to exp[−P/P0], where P=(hf/2e)2/Rn is the power dissipated in the junction at the resonance and P0 is a characteristic power level. The values of P0 for our junctions were around 20 μW at 34...

THz Hilbert-Transform Spectrum Analyzer Based on High-

A demonstrator of a terahertz (THz) Hilbert-transform spectrum analyzer with subsecond scanning times and accuracy of the order of 10-3 has been developed. The spectrum analyzer is based on a high-Tc Josephson junction in a compact Stirling cryocooler. Operation of the spectrum analyzer has been critically considered in the THz range and sources of errors have been studied. The voltage and frequency scales of the analyzer have been calibrated with accuracy of 7 ·10-4 by Shapiro steps, induced on the I(V) curve of the junction by intensive monochromatic radiation. Dynamic errors of the analyzer have been minimized with scanning rates up to 4 THz/s. An instrumental function of the spectrum analyzer is of a Lorentz type with a spectral width of 1.5 GHz and free from any harmonic and subharmonic contributions with accuracy of around 10-3. Rapid and detailed characterization of the THz sources, based on frequency multiplication of microwave radiation, has been demonstrated with the developed spectrum analyzer. The developed spectrum analyzer will be effective in new demanding THz applications, where a combination of high speed and accuracy is required.

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One of future public security techniques will be related with non-invasive, fast and reliable detection of liquids. To distinguish between liquids under concern, we have suggested a concept using our Hilbert spectroscopy, based on high-Tc Josephson junctions. This spectroscopy is the only technique, which covers a frequency range of main dispersions of liquids from a few GHz to a few THz. Several demonstration setups of liquid identifiers, consisting of Hilbert spectrometers integrated on Stirling coolers and polychromatic radiation sources, have been developed. A critical consideration of the main sources of fluctuations in these measurements was carried out and a signal accuracy of around 0.3% has been reached with a total measurement time of a few seconds. Identification of samples of benign and threat liquids was demonstrated.

Josephson Junction in Stirling Cryocooler

Bridging of the terahertz gap in the electromagnetic spectrum between the microwave and infrared ranges requires a variety of new technological developments from basic elements, such as emitters and detectors, to complete systems, such as spectrum analyzers and imagers. As an example of these developments, Hilbert-transform spectral analysis of terahertz radiation sources has been demonstrated. A spectrum analyzer based on a high- Tc square-law Josephson detector has been developed and characterized in the frequency range from 50 to 1800 GHz. Spectra of output terahertz radiation from optically-pumped lasers and frequency multipliers have been studied, and their regimes were optimized for a single-frequency operation. Starting from the optimized multipliers, a polychromatic source has been synthesized and characterized with Hilbert-transform spectrum analyzer.

Josephson Spectroscopy for Identification of Liquids

The longitudinal charge distribution of an electron bunch can be determined from the coherent transition radiation emitted when the bunch crosses a thin metal foil. A Josephson junction made from a thin film of YBa/sub 2/Cu/sub 3/O/sub 7-x/ on a bicrystal substrate is used as a detector for transition radiation in the millimeter and submillimeter range. The spectral intensity of the radiation and the longitudinal form factor of the bunch are derived by applying a Hilbert transformation to the radiation-induced modification of the current-voltage characteristic of the Josephson junction. The physical principles of a Josephson junction as a detector for submillimeter radiation are outlined and a first bunch length measurement is presented.

Terahertz Applications of Hilbert-Transform Spectral Analysis

Abstract Electron cyclotron emission (ECE) from hot tokamak plasmas is recognized nowadays as a very informative diagnostic of main plasma parameters. Among several instruments developed to measure ECE, only a Martin-Puplett interferometer operates in a broadband frequency range of ECE from 70 to 1000 GHz. To derive the absolute radiation temperature of the plasma, a total measurement system, including front-end radiation collection, a transmission line, and the interferometer, is calibrated using a hot/cold calibration source. It takes a long time to calibrate the ECE system because of the high values of the noise equivalent power (NEP). A new technique, Hilbert-transform spectral analysis, is proposed for ITER plasma ECE spectral measurements. The operation principle, characteristics, and advantages of the corresponding Hilbert-transform spectrum analyzer (HTSA) based on a high-Tc Josephson detector are described. Because of the lower NEP values of the Josephson detector, this spectrum analyzer might demonstrate shorter calibration times than those for the Martin-Puplett interferometer. Because of a principal difference between Fourier and Hilbert transforms, the HTSA might have an additional advantage in retrieving harmonic ECE radiation from a continuous thermal background.

A Hilbert transform spectrometer using a high-T/sub c/ Josephson junction for bunch length measurements at the TESLA Test Facility linac

Josephson junctions with high characteristic voltages I_cR_n and resistances R_n ranging from subohm values to several hundred ohms are required for various terahertz (THz) applications. Due to optimization of technology, [100]-tilt YBa₂Cu₃O_7-x bicrystal Josephson junctions with an average I_cR_n (5 K) value of 7 mV at an Rn-range from 0.4 to 400 Ω have been fabricated on (320) bicrystal NdGaO₃ substrates. Classical and frequencyselective detection of THz radiation have been demonstrated with the fabricated Josephson junctions. The main characteristics of Josephson oscillators, spectrum analyzers, admittance spectrometers, and classical detectors have been evaluated within this range of junction parameters, and promising results have been obtained.

Feasibility of ECE Measurements Using Hilbert-Transform Spectral Analysis

To distinguish between liquids in security screening, we have applied Hilbert spectroscopy and high-Tc Josephson detectors. Compact set-ups have been developed and reflection spectra of various liquids in bottles have been measured in the spectral range of 15–300 GHz with scanning times down to 0.2 s.