scholarly journals Electronic Modulation of THz Radiation at NovoFEL: Technical Aspects and Possible Applications

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3063 ◽  
Author(s):  
Oleg A. Shevchenko ◽  
Anatoly R. Melnikov ◽  
Sergey V. Tararyshkin ◽  
Yaroslav V. Getmanov ◽  
Stanislav S. Serednyakov ◽  
...  
Keyword(s):  
Free Electron ◽  
Peak Power ◽  
Time Window ◽  
Far Infrared ◽  
Thz Radiation ◽  
Free Electron Lasers ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
Mid Infrared ◽  
Electron Paramagnetic

The Novosibirsk Free Electron Laser (NovoFEL) facility is able to produce high-power tunable terahertz (THz) laser radiation in quasi-continuous mode. The ability to control/shape this THz radiation is required in a number of user experiments. In this work we propose a modulation approach suitable for free electron lasers based on recuperation design. It allows for generating THz macropulses of a desirable length, down to several microseconds (limited by a quality factor of FEL optical resonator). Using this approach, macropulses in the time window from several microseconds to several hundred microseconds have been shown for three possible frequency ranges: mid-infrared (~1100 cm−1), far-infrared (~200 cm−1) and THz (~40 cm−1). In each case, the observed rise and decay of the macropulse have been measured and interpreted. The advantage of using short macropulses at the maximum peak power available has been demonstrated with the time-resolved Electron Paramagnetic Resonance (EPR) spectroscopy.

The advent of X-ray free electron lasers

Photoniques ◽  
2021 ◽  
pp. 22-26
Author(s):  
Marie-Emmanuelle Couprie
Keyword(s):  
Free Electron ◽  
Peak Power ◽  
Short Pulse ◽  
Far Infrared ◽  
Gain Medium ◽  
High Peak Power ◽  
X Rays ◽  
Free Electron Lasers ◽  
Free Electrons ◽  
X Ray

Free Electron Lasers (FEL) use free electrons in the periodic permanent magnetic field of an undulator as a gain medium. They extend from far infrared to X-rays, they are easily tunable and provide a high peak power. The advent of tunable intense (few mJ) short pulse (down to the attosecond regime) FELs with record multi GW peak power in the X-ray domain enables to explore new scientific areas. These unprecedent X-ray sources come along with versatile performance.

scholarly journals Photoreactivity of Hair Melanin from Different Skin Phototypes—Contribution of Melanin Subunits to the Pigments Photoreactive Properties

2021 ◽  
Vol 22 (9) ◽  
pp. 4465
Author(s):  
Krystian Mokrzynski ◽  
Shosuke Ito ◽  
Kazumasa Wakamatsu ◽  
Theodore G. Camenish ◽  
Tadeusz Sarna ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Singlet Oxygen ◽  
Near Infrared ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
W Band ◽  
Epr Oximetry ◽  
X Band ◽  
Hair Samples ◽  
Electron Paramagnetic

Photoreactivity of melanin has become a major focus of research due to the postulated involvement of the pigment in UVA-induced melanoma. However, most of the hitherto studies were carried out using synthetic melanin models. Thus, photoreactivity of natural melanins is yet to be systematically analyzed. Here, we examined the photoreactive properties of natural melanins isolated from hair samples obtained from donors of different skin phototypes (I, II, III, and V). X-band and W-band electron paramagnetic resonance (EPR) spectroscopy was used to examine the paramagnetic properties of the pigments. Alkaline hydrogen peroxide degradation and hydroiodic acid hydrolysis were used to determine the chemical composition of the melanins. EPR oximetry and spin trapping were used to examine the oxygen photoconsumption and photo-induced formation of superoxide anion, and time-resolved near infrared phosphorescence was employed to determine the singlet oxygen photogeneration by the melanins. The efficiency of superoxide and singlet oxygen photogeneration was related to the chemical composition of the studied melanins. Melanins from blond and chestnut hair (phototypes II and III) exhibited highest photoreactivity of all examined pigments. Moreover, melanins of these phototypes showed highest quantum efficiency of singlet oxygen photogeneration at 332 nm and 365 nm supporting the postulate of the pigment contribution in UVA-induced melanoma.

scholarly journals Two - Color Mid-Infrared Spectroscopy of Isoelectronic Centers in Silicon

2003 ◽  
Vol 770 ◽  
Author(s):  
N.Q. Vinh ◽  
T. Gregorkiewicz
Keyword(s):  
Excited States ◽  
Free Electron ◽  
Free Electron Laser ◽  
Materials Science ◽  
Time Resolved ◽  
Mid Infrared ◽  
Semiconductor Physics ◽  
Open Questions ◽  
Time Resolved Photoluminescence ◽  
Tunable Source

AbstractOne of the open questions in semiconductor physics is the origin of the small splittings of the excited states of bound excitons in silicon. A free electron laser as a tunable source of the mid-infrared radiation (MIR) can be used to investigate such splittings of the excited states of optical centers created by transition metal dopants in silicon. In the current study, the photoluminescence from silver and copper doped silicon is investigated by two color spectroscopy in the visible and the MIR. It is shown the PL due recombination of exciton bound to Ag and Cu is quenched upon application of the MIR beam. The time-resolved photoluminescence measurements and the quenching effects of these bands are presented. By scanning the wavelength of the free-electron laser ionization spectra of relevant traps involved in photoluminescence are obtained. The formation and dissociation of the bound excitons, and the small splittings of the effective-mass excited states are discussed. The applied experimental method allows correlation of DLTS data on trapping centers to specific channels of radiative recombination. It can be applied for spectroscopic analysis in materials science of semicondutors.

scholarly journals Регистрация терагерцового излучения с помощью наноструктур карбида кремния

2021 ◽  
Vol 55 (12) ◽  
pp. 1195
Author(s):  
Н.Т. Баграев ◽  
С.А. Кукушкин ◽  
А.В. Осипов ◽  
Л.Е. Клячкин ◽  
A.М. Маляренко ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Incident Radiation ◽  
Thz Radiation ◽  
Device Structure ◽  
Paramagnetic Resonance ◽  
Kinetic Dependence ◽  
Proposed Model ◽  
Source Current ◽  
Electron Paramagnetic ◽  
The Magnetic Field

The response to external terahertz (THz) radiation from the silicon carbide nanostructures prepared by the method of substitution of atoms on silicon is investigated. The kinetic dependence of the longitudinal voltage is recorded at room temperature by varying the drain-source current in the device structure performed in a Hall geometry. In the frameworks of proposed model based on the quantum Faraday effect the incident radiation results in the appearance of a generated current in the edge channels with a change in the number of magnetic flux quanta and in the appearance of features in the kinetic dependence of the longitudinal voltage. The generation of intrinsic terahertz radiation inside the silicon carbide nanostructures is also revealed by the electrically-detected electron paramagnetic resonance (EDEPR) measured the longitudinal voltage as a function of the magnetic field value.

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