In this paper, we present a review of the latest results obtained in the scope of ghost imaging using auxiliary multiplex channels. The proposed methods make it possible to increase the speed of image acquisition, as well as eliminate distortions in the signal of a bucket detector. One of the most serious limitations of ghost imaging is the large number of measurements required. During the data acquisition, the optical environment where the observation object is located may change its parameters, which will negatively affect the quality of the reconstructed image. To solve these problems, it is possible to use fast spatial light modulators to set structured patterns and fast detectors. However, such equipment is not available in some spectral ranges and is not able to suppress distortions in the detected signal. In this regard, our team has proposed a number of techniques to solve the problems of a large number of measurements and non-stationarity of the optical medium in ghost imaging systems. First of all, an auxiliary polarization channel method was presented in a ghost imaging system to eliminate distortion in the signal of a bucket detector. Secondly, wavelength multiplexing methods have been proposed in the visible and terahertz wavelength ranges. These methods will make ghost imaging systems more applicable to the tasks of remote sensing and mapping of areas in various spectral ranges.
It is known that in the optical range quadratic nonlinear effects in solids appear at relatively low radiation intensities, while the radiation intensity required for a significant manifestation of cubic effects is much higher and can reach the damage threshold values. In this regard, quadratic effects dominate over cubic ones. In this work, it is analytically demonstrated that in the terahertz range the intensities required for the manifestation of cubic effects are much lower than in the optical range. In addition, their contribution to nonlinear effects can exceed the quadratic one by several orders of magnitude.
In this paper we present the results of both experimental and theoretical study of terahertz waves energy enhancement during liquid jets double-pulse excitation. The dependence of the terahertz radiation energy on mutual ratio of the pre-pulse and signal pump energies is investigated. Temperature dependence in the case of double-pulse irradiation reveals unexpected features displaying both exponential growth and decrease with a 18° optimal value.
THz liquid photonics is a new research frontier in laser-matter interaction community. We have successfully demonstrated THz wave generation from ionized liquids, including from liquid water, liquid nitrogen, and liquid gallium. Preferable to general targets, a flowing liquid line provides a fresh area for each excitation pulse, so the chaos and debris caused by the previous pulse will not influence the next one. This makes it possible of using a kHz repetition rate laser for excitation. THz wave generation from ionized liquids presents photoionization processes that are different from those in gases.
We show experimental results on the generation of terahertz radiation in at jets of modified water and various liquids. We compare the change in the efficiency of the THz waves generation with a change in the pH and kH values, as well as the salt concentration in water and the fat level in milk. Dependences of the terahertz radiation energy on the pump pulse energy are demonstrated.
In this work, we considered mixtures of ethanol and water in the form of jets as samples for THz generation based on laser-induced filamentation. The dependence of the output energy of terahertz radiation on the concentration of ethanol in water was experimentally studied. It is shown that the energy grows linearly, which can be explained by an increase in the ionization energy due to the linear replacement of low-efficient charge carriers (water) with highly-efficient (ethanol). The dependence of the THz generation on the optical angle of incidence on the mixture jets was also demonstrated. The results of this study can be further used to create universal source of terahertz radiation.
It is shown experimentally that the near-infrared femtosecond laser irradiation and subsequent thermal treatment of silver-containing silicate glasses result in the formation of luminescent silver molecular clusters (MCs) and silver nanoparticles (NPs). In glasses doped also with halides (mostly Br), the nonluminescent silver NPs are formed because of the presence of halogenide shells on their surfaces, whereas, in glasses with no Br ions, the luminescent silver nanoparticles provides an emission in the 600- to 750-nm range. Two possible mechanisms of luminescence of glass with silver NPs are considered: (i) luminescence of silver NPs without halogenide shell and (ii) the luminescence of silver MCs Agm (m=1 to 4) remaining even after the formation of silver NPs.
Information transfer through single-mode optical fiber by means of quasidiscrete spectral supercontinuums in the 1300- to 1620-nm wavelength range has been demonstrated. Using 16 spectral lines in each supercontinuum at the repetition rate of 70 MHz allows for a 1.1-Gb/s information transfer rate to be achieved. It has been shown that the proposed information transfer method can achieve a 0.8-Tb/s information transfer rate using existing telecommunications equipment.
In this paper the dependence of the coherence time of a femtosecond spectral supercontinuum from different initial pulse
parameters - wavelength, peak intensity and duration is studied. The obtained dependences and ratio of the coherence time
of the pulse to the duration of the pulse at the output are analyzed. It is shown that in the case of femtosecond spectral
supercontinuum generation in fused silica in the areas of normal, anomalous and zero group velocity dispersion, with an
increase of the central wavelength of the femtosecond laser pulse at the input, the coherence time of the radiation with
ultra-wide spectrum is significantly decrease. However, in the region of zero group velocity dispersion of fused silica there
is a "leap" of the coherence time. For example, for the initial pulse duration of 40 fs at 800 nm, the coherence time is 22
fs. With the increase of wavelength, the coherence time reduces to 4 fs at a wavelength of 1180 nm. In the area of zero
group velocity dispersion, the coherence time increases dramatically to 20 fs, after which it decreases, reaching a minimum
of 4 fs at a wavelength of 1560 nm.
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