Generation Of Laser Radiation Research Articles

Generation of laser radiation by nanostructured solid active elements with selective optical nanoresonators formed in nanoporous aluminum oxide films

Generation of laser radiation by nanostructured solid active elements with selective optical nanoresonators formed in nanoporous aluminum oxide films

Enhancing Electron Beam Radiative Energy Extraction Efficiency in Free-Electron Laser Oscillators Through Beam Energy Ramping

Free-electron lasers are used to generate laser radiation using an accelerated electron beam. In this paper, an electrostatic accelerator was used with a thermionic cathode. Lasing pulses of the order of tens of microseconds were generated by passing the current pulses through a wiggler and resonator combination. The change in lasing power as a result of postsaturation variation of the energy of the electron beam during the lasing period is presented in this paper in the form of experimental measurements and simulations. In the experiments, the initial electron beam energy was ~1.4 MeV and the current was 1.13 A, whilst the lasing frequency was always close to 102 GHz. It is shown that postsaturation, positively ramping the beam energy increases the radiation extraction efficiency by around 50%. Whilst a falling beam energy results in a reduction in extraction efficiency.

VENOUS ECTASIA OF THE VERMILION BORDER: COPPER VAPOR LASER TREATMENT

We present the experience of application of "Yakhroma-Med" copper vapor laser system for the treatment of venouse ectasia (VE) of the vermilion border. The yellow wavelength of the generated laser radiation reaches 578 nm falls at the peak of hemoglobin absorption. The treatment was conducted in 58 patients with VE rising above the skin for no more than 1 mm. 100% clinical result. With a hemangioma size of up to 1 cm, treatment efficiency was 87% after the first procedure and complete resolution in 13% of the patients after the second procedure. At a size of more than 1 cm, the efficiency was 71% after the first procedure and 29% after the second. A 100% clinical result was obtained. The therapeutic effect persisted throughout the year in all 58 patients. It has been established that microcirculation disorders processes and further development of VE are affected by a variety of exogenous factors: about a half (48.3%) of the patients were deliberately subjected to excessive sunlight exposure, more than a quarter lived in regions with adverse climatic factors (wind, cold, abnormally low humidity, etc.) (27.6%), or regularly received hyperthermic procedures (steam bath, sauna, etc.) (25.9%). A burn (thermal, chemical) is found in the medical history of one in every five women (20.7%). 17.2% of the patients indulged in excessive consumption of condimental, spicy and hot food.

Generation of laser radiation by nanostructured solid active elements based on nanoporous aluminum oxide films activated with rhodamine 6G

The generation of laser radiation by a solid active element based on a nanoporous aluminum oxide film activated with rhodamine 6G has been obtained for the first time in the geometry to reflection. The lasing is characterized by high-quality radiation with the absence of a spontaneous component. It is found that the application of silicone oil as the immersion substance reduces the generation threshold more than two times. The optimal concentration of rhodamine 6G molecules in the impregnation solution for mirror films of nanoporous aluminum oxide is determined, at which the dye fluorescence intensity has the maximum value. The generation by a nanoporous aluminum oxide film activated with rhodamine 6G in the continuous mode has been obtained for the first time.

Optical Properties of Zinc(II) and Boron(III) Dipyrrinates with Different Structures

The spectral luminescent, photophysical, photochemical, lasing, nonlinear optical, and sensor characteristics of a series of new synthesized complexes of zinc and difluoroborate with dipyrrines of different structure have been studied. It is found that many of these compounds exhibit stimulated emission in different solvents when excited by the second (532 nm) and third (355 nm) harmonics of a Nd:YAG laser in the range of 548–692 nm. It is shown that not only efficient fluorophores belonging to dipyrrine difluoroborates (with a quantum fluorescence yield close to 1), but also compounds with a fluorescence yield equal to 0.3, generate laser radiation with a high resource; phosphorescence is also observed along with fluorescence. Transmission of UV radiation (355 nm) is shown to decrease with an increase in the pulsed excitation power density; this is a manifestation of nonlinear optical properties. The change of phosphorescence signal in dependence of the composition of the gas mixture around a solid-state sample colored by dipyrrinate complexes indicates that a number of the compounds under consideration exhibit sensor abilities.

Advanced properties of extended laser-produced plasmas for efficient generation of the high-order harmonics of ultrashort laser pulses

The review of the studies showing the advanced properties of extended plasma plumes (5 mm) for efficient high-order harmonic generation of laser radiation compared with the short lengths of plasmas (~0.3–0.5 mm) used in previous studies is presented. The harmonic conversion efficiency quadratically increased with the growth of plasma length at the optimal conditions of plasma formation. The studies of this process using the long plasma jets produced on various metal surfaces, particularly including the resonance-enhanced harmonic generation, two-color pump, and extended nanoparticle plasma, are discussed.

Optically transparent mesoporous polymers based on anionic macroinitiators and 2,4-toluene diisocyanate

Optically transparent mesoporous polymers have been synthesized through the anionic polymerization of 2,4-toluene diisocyanate initiated by anionic macroinitiators. The influence of the molecular weight of the macroinitiators on the formation behavior of amphiphilic block copolymers has been considered along with the role of substituted urea in the stabilization of the O-polyisocyanate blocks. The features of the supramolecular organization of mesoporous polymers have been studied. It has been shown that an increase in the proportion of O-polyisocyanate blocks in the coplanar trans configuration in the polymers is accompanied by a significant decrease in their volume electrical resistivity values. The preferential formation of amphiphilic block copolymers is reflected in the formation of highly ordered domains and perfection of the supramolecular cellular geometry of mesoporous polymers. It has been found that the mesoporous polymer structuring enables the immobilization of organic chromophores. It has been shown that luminophores in the cavities of mesopores generate laser radiation and exhibit high resistance to high-power laser radiation.

How phase dispersion of optical coatings affects intracavity second-harmonic generation of laser radiation

This paper discusses how antireflection and reflective optical coatings, as well as the position of a nonlinear crystal inside the cavity, affect intracavity second-harmonic generation. It is shown that phase dispersion of typical antireflection coatings and many reflective coatings is compensated. The phase dispersion of certain types of reflective coatings in this case can introduce a significant contribution to the overall phase dispersion. Dual-frequency reflective coatings are classified with respect to the size of the added part of the generalized phase of the laser wave and its second harmonic. The optimum combinations of types of reflective coatings and the positions of the nonlinear crystal relative to the end mirror are determined for use in lasers with intracavity second-harmonic generation.

Continuous hydroxyl radical planar laser imaging at 50 kHz repetition rate.

This study demonstrates high-repetition-rate planar laser-induced fluorescence (PLIF) imaging of hydroxyl radicals (OH) in flames at a continuous framing rate of 50kHz. A frequency-doubled dye laser is pumped by the second harmonic of an Nd:YAG laser to generate laser radiation near 283nm with a pulse width of 8ns and rate of 50kHz. Fluorescence is recorded by a two-stage image intensifier and complementary metal-oxide-semiconductor camera. The average power of the 283nm beam reaches 7W, yielding a pulse energy of 140μJ. Both a Hencken burner and a DC transient-arc plasmatron are used to produce premixed CH4/air flames to evaluate the OH PLIF system. The average signal-to-noise ratio for the Hencken burner flame is greater than 20 near the flame front and greater than 10 further downstream in a region of the flame near equilibrium. Image sequences of the DC plasmatron discharge clearly illustrate development and evolution of flow features with signal levels comparable to those in the Hencken burner. The results are a demonstration of the ability to make high-fidelity OH PLIF measurements at 50kHz using a Nd:YAG-pumped, frequency-doubled dye laser.

Quantification of different water species in acetone using a NIR-triple-wavelength fiber laser.

A fiber laser using a thulium-doped ZBLAN gain medium was used to generate laser radiation simultaneously at 1461, 1505 and 1874 nm, with > 5 mW output power at each of the wavelengths. The laser was used to quantify the near-infrared absorption of liquid water in acetone. Additionally, near-infrared spectra were recorded using a broad band source and were interpreted using parallel factor (PARAFAC) analysis to rationalize the concentration-dependent peak shifts.

Crystal equivalent temperature model in process of nonlinear conversion of laser radiation

Theoretical modeling was performed for estimation of influence of thermal effects in nonlinear-optical crystals on process of second harmonic generation of laser radiation. Due to absorption of both pump and generated radiation the temperature distribution inside crystal is substantially nonuniform as in cross-section as along its length. Three dimensional heat conduction problem was solved considering two types of heat sources, conditioned by exponential decay and parabolic growth of laser radiation intensity along crystal length. Longitudinal temperature gradient inside crystal is detrimental for process of laser radiation conversion.

Advanced properties of extended plasmas for efficient high-order harmonic generation

We demonstrate the advanced properties of extended plasma plumes (5 mm) for efficient harmonic generation of laser radiation compared with the short lengths of plasmas (∼0.3–0.5 mm) used in previous studies. The harmonic conversion efficiency quadratically increased with the growth of plasma length. The studies of this process along the whole extreme ultraviolet range using the long plasma jets produced on various metal surfaces, particularly including the resonance-enhanced laser frequency conversion and two-color pump, are presented. Such plasmas could be used for the quasi-phase matching experiments by proper modulation of the spatial characteristics of extended ablating area and formation of separated plasma jets.

Quasi-phase-matching of high-order harmonics in multiple plasma jets

Harmonic generation of laser radiation from ionized particles in the extreme ultraviolet range at the conditions of the phase matching between the femtosecond driving field and harmonics is an advanced concept for the development of efficient coherent sources in this spectral region. Here we present experimental evidence of quasi-phase-matched high-order harmonic generation in multiple plasma jets produced during laser ablation of the silver target. We observed both the enhancement of some groups of harmonics along the plateau range and the variation of maximally enhanced harmonic order; additionally we analyzed the influence of the number of plasma jets on the harmonic yield. The enhancement factor of 13 was achieved for the 33th harmonic of Ti:sapphire laser using the five-jet plasma configuration.

Acoustic Plasma Effects in the Diffusion-Cooled Working Medium of an Electric-Discharge CO2 CW Laser*

We have studied the effect of shallow modulation of the discharge current on the burning regime and the plasma parameters of a diffusion-cooled glow discharge in CO2/N2/He laser gas mixtures. We have established that modulation of the discharge current leads to excitation in the discharge of pulsations in the acoustic pressure, the electric current, and the intensity of the generated laser radiation, with the frequency of standing acoustic waves arising in the discharge tube and also with the frequencies of the current modulation, its harmonics, and combinations of all these frequencies with the frequency of the current pulsations in the power supply. We have shown that when self-sustaining resonant oscillations in the discharge current are excited or when the current is modulated, the IR luminescence intensity from the upper laser level of the CO2 molecule and the power of the radiation generated by the laser vary because of plasma heating in the positive column of the discharge, due to its contraction in the acoustic wave field initiated by the current pulsations.

Free-electron laser with a plasma wave wiggler propagating through a magnetized plasma channel

A plasma eigenmode has been employed as a wiggler in a magnetized plasma channel for the generation of laser radiation in a free-electron laser. The short wavelength of the plasma wave allows a higher radiation frequency to be obtained than from conventional wiggler free-electron lasers. The plasma can significantly slow down the radiation mode, thereby relaxing the beam energy requirement considerably. In addition, it allows a beam current in excess of the vacuum current limit via charge neutralization. This configuration has a higher tunability by controlling the plasma density in addition to the γ-tunability of the standard FEL. The laser gain has been calculated and numerical computations of the electron trajectories and gain are presented. Four groups (I–IV) of electron orbits have been found. It has been shown that by increasing the cyclotron frequency, the gain for orbits of group I and group III increases, while a decrease in gain has been obtained for orbits of group II and group IV. Similarly, the effect of plasma density on gain has been exhibited. The results indicate that with increasing plasma density, the orbits of all groups shift to higher cyclotron frequencies. The effects of beam self-fields on gain have also been demonstrated. It has been found that in the presence of beam self-fields the sensitivity of the gain increases substantially in the vicinity of gyroresonance. Here, the gain enhancement and reduction are due to the paramagnetic and diamagnetic effects of the self-magnetic field, respectively.

Conditions for generation of X-ray cherenkov radiation during motion of charges in realistic media

The influence of the spatial distribution of electrons, atoms, and nuclei in condensed media on a medium’s susceptibility and on the conditions for the formation of short-wavelength Cherenkov radiation are considered. It is shown that taking into account the inhomogeneous (atomic and electronic) structure of material media in which fast charged particles travel leads to a change in the effective susceptibility and permittivity in the X-ray range, as compared with cases of model homogeneous media with the same average concentration of electrons. The influence of the distribution functions of electrons and nuclei in a target on the conditions for Cherenkov radiation generation and its parameters and on the threshold energy of fast charged particles required to generate such radiation is studied. It is shown that the function of the spatial distribution of electrons and nuclei in a target affects the conditions for generating laser radiation in the X- and λ-ray ranges (on the problem of X- and λ-ray lasers). The obtained results show that using the Fresnel approximation in the X-ray range is insufficiently justified and can lead to significant errors.

High-order harmonic generation in laser plasma: Recent achievements

Recent studies of high-order harmonic generation of laser radiation in laser-produced plasma show new attractive developments in this field. Those include generation of extended harmonics in plasma plumes, new approaches in application of two-color pump, generation of extremely broadened harmonics, further developments in harmonic generation in clusters (fullerenes, carbon nanotubes, in-situ produced nanoparticles), destructive interference of harmonics from different emitters, resonance-induced enhancement of harmonics, applications of high pulse repetition rate lasers for the enhancement of average power of generating harmonics, observation of quantum path signatures, etc. We review some of these recent developments.

Generation of ultrafast mid-infrared laser by DFG between two actively synchronized picosecond lasers in a MgO:PPLN crystal

We report the difference-frequency generation (DFG) of ultrafast mid-infrared laser radiation around 3 μm between two picosecond laser pulses with the center wavelengths of 800 nm and 1064 nm in a MgO:PPLN crystal at room temperature. The two laser pulses were generated from the actively synchronized picoseconds Ti:sapphire and Nd:YVO4 oscillators. We measured the DFG wavelengths tunable from 3.19–3.29 μm and the output power is potential to be several mW. This experiment proves a possible roadmap for ultrafast mid- and far-infrared laser radiation generation and even for the THz radiation.

Use of carbon-containing materials for efficient high-order harmonic generation of laser radiation

A systematic study of the high-order harmonic generation (HHG) of laser radiation in various carbon-containing plasma plumes (CCPPs) is presented. The materials studied are: graphite, boron carbide, C60, polytetrafluoroethylene, polyethylene, carbon nanotubes, and soot. These studies show that CCPPs present the best plasma media for efficient lower order (from 9th to 19th) harmonic generation, while the harmonic cutoff restricted to the 29th order. The advantages of CCPPs for the harmonic generation are confirmed by comparison of the HHG conversion efficiency with that in Ag and In plasma plumes, where the highest conversion efficiency was reported. Use of two-color pump scheme allows further enhancement of harmonic yield from the CCPPs.

Low-order harmonic generation in metal ablation plasmas in nanosecond and picosecond laser regimes

Low-order harmonics, third and fifth, of IR (1064 nm) laser emission have been produced in laser ablation plasmas of the metals manganese, copper and silver. The harmonics were generated in a process triggered by laser ablation followed by frequency up-conversion of a fundamental laser beam that propagates parallel to the target surface. These studies were carried out in two temporal regimes by creating the ablation plasma using either nanosecond or picosecond pulses and then probing the plasma plume with pulses of the same duration. The spatiotemporal behavior of the generated harmonics was characterized and reveals the distinct composition and dynamics of the plasma species that act as nonlinear media, allowing the comparison of different processes that control the generation efficiency. These results serve to guide the choice of laser ablation plasmas to be used for efficient high harmonic generation of laser radiation.