V. V. Kubarev

Ultra-fast terahertz Schottky diode detector

An ultra-fast terahertz Schottky diode detector with a response time less than 20 ps is presented in the paper. The detector allowed us to measure not only the duration of the light pulses in the Novosibirsk terahertz free electron laser (NovoFEL) but also the time structure of these pulses in unstable regimes. This is important for determining the NovoFEL impulse power and for studying and suppressing its different instabilities.

Powermeters and 2D beam imaging systems on the Novosibirsk terahertz free electron laser

Two types of powermeters for the Novosibirsk terahertz free electron laser (NovoFEL) are considered in this paper. The first one is an expositional etalon device on the basis of a heat isolated sapphire plate. The calorimeter is shown to have a constant emissivity of 0.74 in the entire generation range of NovoFEL. The second device is a CW calorimeter with a special absorption cone with an Al2O3 ceramic coating made by a gas dynamic method. Two 2D beam imaging systems with 152 mm times 152 mm workspace are presented. The first one is a thermofluorescent screen with an optical video camera, and the second one is a scanning ID line of thirty piroelectric detectors. Small beams and objects will be investigated by a commercial Pirocam III piroelectric camera with 12 mm times 12 mm workspace.

Status of the Novosibirsk high power free electron laser

The first stage of Novosibirsk high power free electron laser (FEL) was commissioned in 2003. It is based on normal conducting CW energy recovery linac. Now the FEL provides electromagnetic radiation in the wavelength range 120-180 micron. The average power is 100 W. The measured linewidth is 0.3%, which is close to the Fourier-transform limit. The assembly of user beamline is in progress. Plans of future developments are discussed.

Influence of Intense THz Radiation on Spin State of Photoswitchable Compound Cu(hfac)2LPr

The family of magnetoactive compounds Cu(hfac)(2)L(R) exhibits thermo- and photoswitching phenomena promising for various applications. Photoswitching of the Cu(hfac)(2)L(Pr) compound can be observed at temperatures below 20 K and is accompanied by transition to metastable structural state. Reverse conversion to stable structure could not be induced by light of near-IR-vis-UV regions up to date. The far-IR spectra of metastable and stable structural states are different and show characteristic absorption lines in the range of 170-240 cm(-1). These frequencies are accessible by NovoFEL - high-power THz free-electron laser user facility in Novosibirsk. We investigate selective influence of THz radiation on relaxation processes from metastable to stable structural state, which can be monitored by electron paramagnetic resonance (EPR). For this purpose, the experimental station based on X-band EPR spectrometer has been constructed by the THz beamline of NovoFEL and equipped with multimodal THz waveguide allowing to fed radiation directly into the EPR resonator. It has been found that irradiation of studied compound with high-power THz light causes significant but nondestructive increase of its temperature. Apart from this effect, no resonant influence of THz irradiation on relaxation processes has been observed. The experimental results have been rationalized taking into account vibrational relaxation times of the studied compound. Further experiments based on pulse heating by THz radiation have been proposed.

Harmonic Generation in the Novosibirsk Terahertz Free Electron Laser

At the present time, the radiation of the main first harmonic of the Novosibirsk terahertz free electron laser (FEL) lies in the range of 120-230 mum with power level of up to 400 W. The radiation of second and third harmonics was experimentally found in the FEL. This high harmonic FEL radiation extends its spectral range by a factor of 3. Rather high second harmonic radiation unusual for typical FEL allows uninterrupted radiation in the range of 40-230 mum.

1-D and 2-D metal mesh based quasi-optical selective components for high-power applications at Novosibirsk terahertz FEL

In this report we discuss main types of metal mesh based selective components of THz-quasi-optics required for applications in experiments at Novosibirsk terahertz free electron laser. The first experimental results on development of thin-film metal mesh polarizers and frequency filters by photolithographic and electroforming techniques are presented.

High power THz applications on the NovoFEL

High power THz applications on the Novosibirsk terahertz free electron laser are described.

Optical properties of CVD-diamond in terahertz range and its applications on the NovoFEL

The optical properties of a CVD-diamond in the terahertz range were studied by three different independent methods. A very stable universal gas laser was used to measure precisely the CVD transmittance. A method of vacuum Fourier spectroscopy was applied to investigate the frequency dependencies. The absorption coefficient of the CVD-diamond was determined directly by a calorimetric method on the Novosibirsk terahertz free electron laser.

Fourier spectroscopy of water vapor absorption in 40 m optical transport channel of the NovoFEL

Radiation of the Novosibirsk terahertz free electron laser (NovoFEL) is transported to user stations by a 40 m long optical channel. A high vacuum volume of the NovoFEL and the optical channel are separated by a CVD-diamond window. Because of a sufficiently large size of submillimeter beams and the absence of chip and firm vacuum windows of an adequate size, we use a nitrogen-filled channel at normal atmospheric pressure and thin polypropylene windows for radiation coupling on the user stations. The main problem of the long channel is water vapor absorption. A special system of drying with round circulation was made on the basis of a zeolite absorber. A combination of Fourier and free electron laser spectroscopy of the system is presented in this paper.

High Speed Terahertz Imaging Using Thermosensitive Elements

We have studied sensitivity, linearity, dynamic range, space and time resolution of three imaging systems for the visualization of high-power radiation from 0.12 to 0.25 mum: an IR-thermograph, a phosphor screen sensitive to thermal quenching of luminescence, and a glass-plate visible-light interferometer.