In vivo analysis of THz wave irradiation induced acute inflammatory response in skin by laser-scanning confocal microscopy.

The recent development of THz sources in a wide range of THz frequencies and power levels has led to greatly increased interest in potential biomedical applications such as cancer and burn wound diagnosis. However, despite its importance in realizing THz wave based applications, our knowledge of how THz wave irradiation can affect a live tissue at the cellular level is very limited. In this study, an acute inflammatory response caused by pulsed THz wave irradiation on the skin of a live mouse was analyzed at the cellular level using intravital laser-scanning confocal microscopy. Pulsed THz wave (2.7 THz, 4 µs pulsewidth, 61.4 µJ per pulse, 3Hz repetition), generated using compact FEL, was used to irradiate an anesthetized mouse's ear skin with an average power of 260 mW/cm(2) for 30 minutes using a high-precision focused THz wave irradiation setup. In contrast to in vitro analysis using cultured cells at similar power levels of CW THz wave irradiation, no temperature change at the surface of the ear skin was observed when skin was examined with an IR camera. To monitor any potential inflammatory response, resident neutrophils in the same area of ear skin were repeatedly visualized before and after THz wave irradiation using a custom-built laser-scanning confocal microscopy system optimized for in vivo visualization. While non-irradiated control skin area showed no changes in the number of resident neutrophils, a massive recruitment of newly infiltrated neutrophils was observed in the THz wave irradiated skin area after 6 hours, which suggests an induction of acute inflammatory response by the pulsed THz wave irradiation on the skin via a non-thermal process.

Generating high-power short terahertz electromagnetic pulses with a multifoil radiator.

We describe a multifoil cone radiator capable of generating high-field short terahertz pulses using short electron bunches. Round flat conducting foil plates with successively decreasing radii are stacked, forming a truncated cone with the z axis. The gaps between the foil plates are equal and filled with some dielectric (or vacuum). A short relativistic electron bunch propagates along the z axis. At sufficiently high particle energy, the energy losses and multiple scattering do not change the bunch shape significantly. When passing by each gap between the foil plates, the electron bunch emits some energy into the gap. Then, the radiation pulses propagate radially outward. For transverse electromagnetic waves with a longitudinal (along the z axis) electric field and an azimuthal magnetic field, there is no dispersion in these radial lines; therefore, the radiation pulses conserve their shapes (time dependence). At the outer surface of the cone, we have synchronous circular radiators. Their radiation field forms a conical wave. Ultrashort terahertz pulses with gigawatt-level peak power can be generated with this device.

Influence of intense THz radiation on spin state of photoswitchable compound Cu(hfac)2L(Pr).

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.

Studying the non-thermal effects of terahertz radiation on E. coli/pKatG-GFP biosensor cells.

Studies of the impact of terahertz radiation on living objects present a significant interest since its use for security systems is currently considered promising. We studied the non-thermal impact of terahertz radiation on E. coli/pKatG-gfp biosensor cells. The Novosibirsk free electron laser (NovoFEL), which currently has the world's highest average and peak power, was used as the source of terahertz radiation. We demonstrated that exposure to terahertz radiation at the wavelengths of 130, 150, and 200 µm and a power of 1.4 W/cm(2) induces changes in green fluorescent protein (GFP) fluorescence values and thus induces the expression of GFP in E. coli/pKatG-gfp biosensor cells. Possible mechanisms of the E. coli response to non-thermal exposure to terahertz radiation are discussed.

Real-time ultrafast oscilloscope with a relativistic electron bunch train.

The deflection of charged particles is an intuitive way to visualize an electromagnetic oscillation of coherent light. Here, we present a real-time ultrafast oscilloscope for time-frozen visualization of a terahertz (THz) optical wave by probing light-driven motion of relativistic electrons. We found the unique condition of subwavelength metal slit waveguide for preserving the distortion-free optical waveform during its propagation. Momentary stamping of the wave, transversely travelling inside a metal slit, on an ultrashort wide electron bunch enables the single-shot recording of an ultrafast optical waveform. As a proof-of-concept experiment, we successfully demonstrated to capture the entire field oscillation of a THz pulse with a sampling rate of 75.7 TS/s. Owing to the use of transversely-wide and longitudinally-short electron bunch and transversely travelling wave, the proposed "single-shot oscilloscope" will open up new avenue for developing the real-time petahertz (PHz) metrology.

THz-pump and X-ray-probe sources based on an electron linac.

We describe a compact THz-pump and X-ray-probe beamline, based on an electron linac, for ultrafast time-resolved diffraction applications. Two high-energy electron (γ > 50) bunches, 5 ns apart, impinge upon a single-foil or multifoil radiator and generate THz radiation and X-rays simultaneously. The THz pulse from the first bunch is synchronized to the X-ray beam of the second bunch by using an adjustable optical delay of a THz pulse. The peak power of THz radiation from the multifoil radiator is estimated to be 0.14 GW for a 200 pC well-optimized electron bunch. GEANT4 simulations show that a carbon foil with a thickness of 0.5-1.0 mm has the highest yield of 10-20 keV hard X-rays for a 25 MeV beam, which is approximately 103 photons/(keV pC-electrons) within a few degrees of the polar angle. A carbon multifoil radiator with 35 foils (25 µm thick each) can generate close to 103 hard X-rays/(keV pC-electrons) within a 2° acceptance angle. With 200 pC charge and a 100 Hz repetition rate, we can generate 107 X-rays per 1 keV energy bin per second or 105 X-rays per 1 keV energy bin per pulse. The longitudinal time profile of an X-ray pulse ranges from 400 to 600 fs depending on the acceptance angle. The broadening of the time duration of an X-ray pulse is observed owing to its diverging effect. A double-crystal monochromator will be used to select and transport the desired X-rays to the sample. The heating of the radiators by an electron beam is negligible because of the low beam current.

Development of an S-band cavity-type beam position monitor for a high power THz free-electron laser.

A cavity-type beam position monitor (BPM) has been developed for a compact terahertz (THz) free-electron laser (FEL) system and ultra-short pulsed electron Linac system at the Korea Atomic Energy Research Institute (KAERI). Compared with other types of BPMs, the cavity-type BPM has higher sensitivity and faster response time even at low charge levels. When electron beam passes through the cavity-type BPM, it excites the dipole mode of the cavity of which amplitude depends linearly on the beam offset from the center of the cavity. Signals from the BPM were measured as a function of the beam offset by using an oscilloscope. The microtron accelerator for the KAERI THz FEL produces the electron beam with an energy of 6.5 MeV and pulse length of 5 µs with a micropulse of 10-20 ps at the frequency of 2.801 GHz. The macropulse beam current is 40 mA. Because the microtron provides multi-bunch system, output signal would be the superposition of each single bunch. So high output signal can be obtained from superposition of each single bunch. The designed position resolution of the cavity-type BPM in multi-bunch is submicron. Our cavity-type BPM is made of aluminum and vacuum can be maintained by indium sealing without brazing process, resulting in easy modification and cost saving. The resonance frequency of the cavity-type BPM is 2.803 GHz and the cavity-type BPM dimensions are 200 × 220 mm (length × height) with a pipe diameter of 38 mm. The measured position sensitivity was 6.19 (mV/mm)/mA and the measured isolation between the X and Y axis was -39 dB. By measuring the thermal noise of system, position resolution of the cavity-type BPM was estimated to be less than 1 µm. In this article, we present the test results of the S-band cavity-type BPM and prove the feasibility of the beam position measurement with high resolution using this device.