Options for using ordered 3D arrays of photonic crystals for the generation of gigahertz, optical, and neutron radiation upon interaction with a beam of high-energy electrons are considered. The optical emission spectra of photonic crystals produced in the interaction with a beam of relativistic electrons are presented. Experiments were carried out to obtain 2D images of objects in gamma and neutron fluxes generated in the interaction of an electron beam with a photonic crystal material. Various neutron generating targets are considered, for which the corresponding neutron yields were calculated. The characteristics of electromagnetic and neutron fields obtained in the experiment are also presented.

As part of the commissioning work at the linear electron accelerator LINAC-200 (JINR), we conducted experiments to study the characteristics of a pulsed neutron source obtained by irradiating a converter target with a 140 MeV electron beam. To estimate neutron source parameters and neutron energy spectra in lead and tungsten targets with different sizes numerical simulations were performed. Additionally, we have conducted experiments to measure the energy spectra of neutrons and gamma rays using high-resolution time-of-flight method. It has been found that the ratio of integral estimates between the calculated and average measured neutron yields (for tungsten and lead targets) did not exceed 30%. The fluence of resonant and thermal neutrons in the target is estimated at 2.8x1013 x 10 13 neutrons per second, which corresponds to the requirements for modern pulsed neutron sources.

In this work, the generation of electromagnetic radiation of a wide spectrum, including microwave and terahertz ranges using three-dimensional ordered nanostructures such as photonic crystals were measured. Generation occurred when the exciting electron beam, created by linear accelerator LINAC-200, passed along the planes of orientation of the globules of the photonic crystal. By varying the orientation of the photonic crystal relative to the electron beam and the beam energy, a tunable narrowband microwave and terahertz source with a peak power at 10 W was created. Our experiments involved a set of photonic crystals with different globule diameters and elemental compositions and also included comparative studies using samples of dielectric and semiconductor monocrystals and powders with monodisperse globule sizes. We found that that electromagnetic radiation from single crystals has a similar frequency structure to that of a photonic crystal in the form of a set of narrow-band peaks with a width at half maximum of similar to several MHz appearing in the case, when the beam is passing along the crystallographic orientation axis of the single crystal.

In this article, a method of depositing plasmonic particles on synthetic opal matrices was used for increasing the efficiency of laser-induced breakdown spectroscopy. The fundamental radiation, second and third harmonics of a picosecond neodymium laser were used to generate plasma. The dependences of the gain factor on the size of the laser spot, as well as on the concentration of silver particles, were obtained. The maximum signal amplification exceeding an order of magnitude was achieved at a wavelength of 1064 nm, corresponding to the localization of the plasmon resonance mode in the gap between closely spaced particles. Emission stability when using particles also increases at all laser wavelengths used. Conducted computer simulation confirmed the results of the experiment. High sensitivity of the method allows its use for monitoring even a small amount of impurity elements and their dynamics during the synthesis of photonic crystals, as well as the dynamics of the process of filling them with various materials during infiltration.

In this paper, we introduce a novel approach to control the random lasing based on multiphoton luminiscence in Zinc oxide (ZnO) nanoparticle water suspension during its guided freezing process. The freezing process leads to the formation of a particle layer on the ice surface, consequently reducing the photon’s scattering mean free path in the medium, as well as increase in the efficiency of the second harmonic generation. This results in a lowered random lasing threshold in the system. The post freezing threshold, under the 355 nm wavelength excitation, decreases by an order of magnitude. These effects may have several applications, including the phase transition sensing, monitoring the evolution of porous structures via the ice-templating technique, controlling the random lasing mode, and enhancing various nonlinear optical processes’ effectiveness for nanoparticles and sub-micron particles in suspensions.

We present a brief review of experimental work on the investigation of stimulated low-frequency Raman scattering of light in systems of submicron and nanosized particles of various physical nature.

Stimulated Raman scattering (SRS) in barium nitrate powder was studied in two temporal modes: excitation by laser pulses of 11 ns and 30 ps from the room temperature to the temperature of liquid nitrogen. For the first time, an increase in the efficiency of SRS conversion by two orders of magnitude was observed when the sample temperature was lowered from room temperature to the temperature of liquid nitrogen. The maximum achieved value of the conversion efficiency was 30 percent. Temporal characteristics of all the SRS components registered in transient mode were measured. The detected effect of the pump energy influence on the delay time of the first Stokes component can be used for measuring the nonlinear parameters of the medium.

Passive Q-switching of a ruby laser using stimulated low-frequency Raman scattering of light has been implemented. Suspensions of submicron dielectric and metal particles were used inside a laser cavity as a Q-switching device. The Q-factor of the resonator changed due to stimulated inelastic scattering by the coherent acoustic vibrations of particles. It has been shown that the pulse duration can vary from tens of nanoseconds to microseconds by changing the characteristics of the submicron system. The advantage of this method of passive Q-switching in comparison with a saturable dye is shown.

The development of new methods for generating pulsed electromagnetic microwave radiation is currently an actively developing area of research. Schemes for microwave radiation generation with optical pumping are of great interest. In this paper we propose and experimentally demonstrate principally new method for photonic generation of microwave electromagnetic radiation. This method is based on the use of radiation of charged submicron particles oscillating at their own acoustic frequency. Laser radiation of the optical range implements an effective buildup of acoustic vibrations of submicron particles forming the system under study, according to the Raman mechanism.

We experimentally register stimulated low-frequency Raman scattering (SLFRS) in the suspension of brome mosaic virus (BMV) in phosphate buffer with very high conversion efficiency. We identify two components of the SLFRS spectrum as the breathing and quadrupole modes of BMV and determine damping characteristics and gain factors for these modes. We show that, using the core–shell model for BMV and taking into account the influence of the environment, the acoustic properties of individual components of such a composite nanosystem can be determined. Thus, we define the sound velocity in the RNA core of BMV, in view of spectral characteristics of SLFRS.

We present the scope of research of a new collaboration FLAP (Fundamental & applied Linear Accelerator Physics collaboration) devoted to the study of the basics of electromagnetic interactions and new applications of controllable generation of electromagnetic radiation by relativistic electrons using functional materials.

The process of switching a short vacuum gap using an auxiliary discharge over the surface of a dielectric is studied by the high-speed recording of images of the plasma in the optical spectral range. Based on the analysis of the obtained experimental data, it is suggested that the cathode spot and cathode flame in the ultraviolet spectral range play a significant in the formation of current channel in the discharge.

Currently, work is underway to create laser accelerators with beam focusing by plasma lenses. For effective focusing, it is necessary to investigate at which initiation of breakdown a discharge forms with a more uniform distribution of current density. Our studies have shown that the plasma distribution is uniform over a longer period of time, including the region of maximum current, if the discharge is initiated by an electron beam.

We study the gas discharge process under conditions when a relativistic electron beam is injected into the discharge tube after applying a high-voltage pulse. As a result, a plasma channel is created, a breakdown occurs, and a discharge develops. Comparative experiments were performed at different gas pressures under discharge conditions with and without electron beam initiation. They showed significant differences, especially during pinching and further development of the discharge.

The process of switching a short vacuum gap by an auxiliary discharge over the dielectric surface was studied via recording of images of discharge plasma radiating in the optical spectral range. A two-channel electro-optical (EO) image-recording system based on an EO converter (EOC) was used. Each channel contained a unit for generating an EOC-photocathode gating pulse, a transposing objective lens, and an EOC, which was joined to a digital CCD (charge-coupled device) camera for reading information from the EOC screen. Based on the analysis of the obtained experimental data, it was suggested that the radiation of a cathode spot and a cathode flame in the UV range play a significant role in the formation of a current channel in the discharge.

Switching of a short vacuum gap with an auxiliary discharge over the surface of a dielectric has been studied via high-speed recording of images of discharge plasma radiating in the optical spectral range. Based on the analysis of experimental data, we surmise that the cathode spot and cathode flame radiation play an important role in the formation of the current channel in the discharge.

Abstract Efficient electromagnetic emission of radiation in the spectral range with wavelengths shorter than exciting light wavelength was observed at the nanomaterials excitation by laser pulses. Emission was registered in a visible (blue-green) range, in vacuum UV and in soft X-ray. Luminescence was registered both in the air and in the vacuum chamber. Synthetic opal matrices and nanocomposites on their base (matrices infiltrated with different liquids) were used as samples. Luminescence was excited with the help of different lasers: ruby laser, second harmonic of Nd:YAG laser and copper vapor laser. In the visible range two regimes of luminescence were observed: fast (few μs) and slow (up to 12 s). Slow luminescence was registered at temperatures lower than 110 K. Spectra of X-ray emission were registered. The connection of this emission with the triboluminescence effect is considered.

Study of the electromagnetic fields interaction with structured nanomaterials with photonic band gaps is one of the most rapidly developing areas of nanophotonics. In modern optics, such nanomaterials are actively used to process the characteristics of electromagnetic radiation. Firstly, the properties of amplification of the local field are used, secondly, the properties of the photonic bandgap. A typical example of local field amplification is the work [1], in which the authors used a coating of submicron dielectric spheres on a copper target in order to achieve more than tenfold increasing the efficiency of X-ray generation. Using the properties of the photonic band gap leads to the increasing well-known nonlinear effects efficiency and to the appearance of new nonlinear phenomena. One of these phenomena is anti-Stokes cryoluminescence in nanomaterials - light emission at low temperature under laser action in the spectral range with higher frequency than that of exciting light. We observed bright and long (up to few seconds) emission in blue-green range under 20ns ruby laser pulses excitation in different nanomaterials at low temperatures [2-3]. One of the reasons of this effect is triboluminescence, free radicals appearing and structure defects forming, like in bulk materials [4]. In the present work we show that in nanomaterials of different nature there are two types of temporal dependence: short (few microseconds) and long (up to 10-12 seconds). Long dependence exists at temperatures lower than 110 K. Temporal dependence for anti-Stokes luminescence in synthetic opal matrices for temperatures lower and higher this threshold is shown in Figure 1.