Generation Of Laser Radiation Research Articles

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.

Continuous chemical HF laser with a modified radially expanding nozzle unit

dium. It was shown that the process of laser radiation generation involves only that part of the active medium that has fairly low values of the static pressure and temperature. Obviously, the creation of conditions for involving the entire volume of the active medium in the generation process is promising for further enhancement of HF laser energy parameters. This can be achieved, in particular, by adding an additional quantity of inert diluent to the active medium of the laser. In [2], we proposed a method for such addition. This method was realized in practice in an autonomous HF laser with a modified radially expanding nozzle unit of original design operating according to the "nozzle–injector–injector" scheme of mixing the reactants. The modified nozzle unit is equipped with a special injector for injecting a cold inert diluent at the inlet to the nozzle and thus realizing the above mixing scheme. Such injection permits separated supply of atomic fluorine and inert diluent into the nozzle, as well as two-region mixing of reactants with subsequent low-temperature flow of the oxidizing gas (mixture F+DF+He) in the supersonic parts of the nozzles. We have modified two available models of the laser under consideration. One of them is a small-size laser (the size of the outlet section of the nozzle unit is 18 × 3.9 cm) with a total mass flow of reactants m Σ 30 g ⁄ s. The other model ia a medium-size laser (the outlet section of the nozzle unit is 35 × 10 cm) with a total mass flow of reactants m Σ 140 g ⁄ s. The results of experiments with the small-size laser with a design power N = 5 kW [2, 3] have shown convincingly that the use of the new method of obtaining oxidizing gas makes it possible to enhance considerably the HF laser energy characteristics. For example, if 95% of the inert diluent (helium) is transferred from the first mixing zone (combustion chamber) to the second one (inlet part of the nozzles), then the laser power can increase by a factor of 2.5 and the specific energy of the laser can increase by a factor of 1.6 as compared to the characteristics of the base model. In the course of experiments with the medium-size HF laser (design power N 20 kW), its workability has been demonstrated. However, the energy characteristics of such a laser turned out to be lower than in the base model.

Time-resolved spectroscopy of plasma plumes: A versatile approach for optimization of high-order harmonic generation in laser plasma

The time-resolved studies of laser-produced Ag, In, Pt, V, Mn, and Ga plasmas are presented from the point of view of plasma application as the nonlinear optical medium for high-order harmonic generation of laser radiation. We show that optimization of plasma formation using this technique allows the enhancement of harmonic generation efficiency and extension of maximal harmonic order.

Second harmonic generation of laser radiation in uniaxial crystals. Alternate problem solutions in the assumed field approximation

General questions of the theory of the second harmonic generation of laser radiation in uniaxial crystals are discussed. The derivation of the integral equations determining the form of the interacting fields on an observation plane situated at an arbitrary distance behind the crystal is presented. It is suggested to solve these equations with boundary conditions specified on the same observation plane. It is shown that such a nontraditional choice of the plane of the specification of the boundary conditions allows for a significant simplification of the sought-after second harmonic field representation in the assumed field approximation.

Application of nanoparticle-containing laser plasmas for optical harmonic generation

Nanoparticle-containing media can be used for efficient high-order harmonic generation of laser radiation. We present the results of studies of the harmonics generated in the laser-produced plasmas containing Cr2O3, Ag, Cu, and Au nanoparticles. These results are compared with the harmonics generated in the plasma produced on the surface of bulk targets at different delays between the subnanosecond heating prepulse and femtosecond pulse and different intensities of prepulse on the target surface. We discuss the harmonic enhancement, which was observed in the case of nanoparticle-containing plumes with regard to the monoparticle-containing plasmas. Morphological studies of plasma debris confirmed the presence and integrity of nanoparticles in the plumes.

An experimental setup for exciting semiconductors and dielectrics with picosecond electron-beam and electric-field pulses

An experimental facility for forming high-voltage pulses with amplitudes of 30–250 kV and durations of 100–500 ps and electron beams with a current density of up to 1000 A/cm2 is described. The facility was built using the principle of energy compression of a pulse from a nanosecond high-voltage generator accompanied by the subsequent pulse sharpening and cutting. The setup is equipped with two test coaxial chambers for exciting radiation in semiconductor crystals by an electron beam or an electric field in air at atmospheric pressure and T = 300 K. Generation of laser radiation in the visible range under field and electron pumping was attained in ZnSSe, ZnSe, ZnCdS, and CdS (462, 480, 515, and 525 nm, respectively). Under the exposure to an electric field (up to 106 V cm−1), the lasing region was as large as 300–500μm. The radiation divergence was within 5°. The maximum integral radiation power (6 kW at λ = 480 nm) was obtained under field pumping of a zinc selenide sample with a single dielectric mirror.

Luminescence and generation of laser radiation in zinc selenide and cadmium sulfide single crystals exposed to high-voltage subnanosecond pulses

The action of high-voltage subnanosecond pulses on AIIBVI semiconductor compounds is studied. A negative pulse with a duration of up to 500 ps is applied to electrodes of a special shape. The pulse amplitude can be varied from 20 to 250 kV. Plane-parallel plates with a thickness of 1–2 mm made of bulk zinc selenide or cadmium sulfide single crystals are placed between the electrodes. Experiments are carried out in air without submerging single crystal plates in a liquid dielectric medium. As soon as a voltage pulse is applied, diverging discharges propagate from sharp edges of the negative electrode along electric field lines. With increasing voltage, generation of laser radiation is observed in the bulk of the semiconductor, displaying all its characteristic features, such as a sharp increase in the radiation power, narrowing the spectrum, and the radiation directionality. For zinc selenide at room temperature, the radiation characteristics are as follows: the wavelength is 480 nm, the radiation divergence is about 3°, and the peak pulse power is 600 W.

Concentrated solar energy conversion to powerful laser radiation on neodymium activated yttrium-aluminum garnet

The first results of experimental investigations concerning laser radiation generation with pumping by concentrated solar radiation flux at the Big Solar Furnace of Materials Science Institute of Uzbek Academy of Sciences are presented.

Synthesis and structure of CsLi0.5Al0.5PO4

A new phosphate CsLi0.5Al0.5PO4 with a structure related to the β-tridymite structure has been synthesized by a precipitation method. X-ray powder diffraction, electron probe microanalysis, second harmonic generation of laser radiation, and IR spectroscopy have been used for studying the compound. Differential scanning calorimetry shows that the synthesized phosphate undergoes phase transitions at Ttr = 68 and 130°C. The crystal structure of CsLi0.5Al0.5PO4 was refined on the basis of X-ray powder diffraction data by the Rietveld method in space group P21/a (Z = 8) with the unit cell parameters a = 17.8323(3) A, b = 5.4250(1) A, c = 9.3666(2) A, β = 89.984(8)°, V = 906.10(9) A3.

Polymeric Active Media for Generating Laser Radiation

Polymeric Active Media for Generating Laser Radiation

High-Power Laser Performance of ${\hbox {Yb:}}{\hbox {YAl}}_{3}({\hbox {BO}}_{3})_{4}$ Crystals Cut Along the Crystallographic Axes

High-power continuous-wave laser operation near 1 mum was demonstrated at room temperature with c-cut and a-cut Yb:YAl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystals end-pumped by a fiber-coupled diode laser. Using a 2-mm-thick c-cut crystal, 10.6 W of output power was generated with an optical-to-optical efficiency of 65% and a slope efficiency of 72%. The complex polarization state of the generated laser radiation was also studied. With a 2-mm-thick a-cut crystal, sigma-polarized laser oscillation was obtained, producing a maximum output power of 8.1 W; the optical-to-optical and slope efficiencies were 56% and 61%, respectively. Complete absorption and emission cross section spectra of the Yb:YAl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystal were also derived, revealing very strong anisotropy of the spectroscopic properties

Parametric amplification and compression to ultrashort pulse duration of resonant linear waves

We report on an optical parametric amplification system which is pumped and seeded by fiber generated laser radiation. Due to its low broadening threshold, high spatial beam quality and high stability, the fiber based broad bandwidth signal generation is a promising alternative to white light generation in bulky glass or sapphire plates. We demonstrate a novel and successful signal engineering implemented in a setup for parametric amplification and subsequent recompression of resonant linear waves resulting from soliton fission in a highly nonlinear photonic crystal fiber. The applied pump source is a high repetition rate ytterbium-doped fiber chirped pulse amplification system. The presented approach results in the generation of ~50 fs pulses at MHz repetition rate. The potential of generating even shorter pulse duration and higher pulse energies will be discussed.

ZnSe:Cr2+ coherently pumped laser

ZnSe:Cr2+ lasers coherently pumped either by flashlamp-pumped Er:YAP (wavelength 1.66μm) or diode pumped Tm:YAP (wavelength 1.97μm) laser radiations were characterized and compared. The maximal ZnSe:Cr2+ laser output pulse energy was 14mJ with the slope efficiency 70% for Er:YAP pump. With the help of dispersive prism inside the resonator, the generated laser radiation was tunable from 2.15μm to 2.6μm with only 3 times drop in laser output energy. With pumping by Tm:YAP laser radiation the pulsed as well as cw regime was investigated. In case of cw the output was 200mW for absorbed power of 300mW with the slope efficiency 66%. The temporal profile and spatial structure of the generated laser beam were measured for both pumping arrangements.

Crystal structure and nonlinear optical properties of the K2UO2(SO4)2 · 2H2O compound at 293 K

Single crystals of potassium uranyl sulfate are grown, and their atomic structure is determined using X-ray diffraction analysis. The compound crystallizes in the orthorhombic crystal system with space group Pna2{sub 1} [a = 13.773(4) A, b = 7.288(2) A, c = 11.556(4) A, R{sub 1} = 0.033, wR{sub 2} = 0.0892 for 2630 reflections with I > 2{sigma}(I)]. The crystal structure of the K{sub 2}UO{sub 2}(SO{sub 4}){sub 2} . 2H{sub 2}O compound is built up of two-dimensional infinite, negatively charged layers of the composition [UO{sub 2}(SO{sub 4}){sub 2}.H{sub 2}O]{sub 2{infinity}}{sup {delta}}{sup -}], which are linked together through the K{sup +} ions. The specific features of the atomic arrangement in the structure of this compound are analyzed, and the second harmonic generation of laser radiation is investigated.

A CO2 Laser with Continuous and Pulse-Periodical Modes of Operation for Surgical Application in Medicine

ABSTRACTCO2 lasers with a longitudinal discharge and a slow gas flow can be used for surgical operations in medicine. This specific application defines certain requirements to the optical parameters of the generated laser radiation. They should be met by variations of the electric regime of the gas-discharge media. The present work is dedicated to the development and study of a control unit providing continuous and pulse-periodical modes of CO2 laser operation, in accordance with the requirements for medical application.

Spatial and energy parameters of laser radiation and second harmonic upon self-frequency doubling

The intracavity second-harmonic generation of laser radiation in an active nonlinear crystal is studied. The spatial distributions of the intensity and power of laser radiation and its second harmonic are calculated by the method of numerical simulations as functions of the parameters of the resonator, active nonlinear crystal, and pump. The analysis is performed for a periodically poled Nd:Mg:LiNbO3 crystal taking diffraction into account.

Nonlinear optical properties of polymer-dispersed liquid-crystalline systems based on fullerene-doped 2-cyclooctylamino-5-nitropyridine

Holographic recording of thin diffraction gratings by nano-and picosecond laser pulses λ=532 nm) is studied in polymerdispersed liquid-crystalline structures based on photosensitive molecules of 2-cycloocty-lamino-5-nitropyridine sensitized with C70 fullerene. Using experimental data, nonlinear refraction n 2 and nonlinear third-order susceptibility χ(3) are calculated for the first time. The obained values determine the potential of the studied media for the modulation and frequency generation of laser radiation in the visible spectral range.

Study of nonlinear optical characteristics of various media by the methods of z-scan and third harmonic generation of laser radiation

The nonlinear optical parameters of colloidal solutions of metals, semiconductor chalcogenide films, vapours and solutions of organic dyes, as well as of fullerene-doped polyimide films are studied by the methods of z-scan and third harmonic generation (THG). The nonlinear refractive indices, nonlinear susceptibilities, and nonlinear absorption coefficients of these materials are measured at the fundamental 1064-nm emission wavelength of a 35-ps pulsed Nd:YAG laser and its second harmonic at 532 nm. The study of the optical limitation of picosecond and nanosecond light pulses in these media showed that the appearance of the long-wavelength absorption band at the final stage of aggregation of colloidal metals resulted in nonlinear absorption of picosecond pulses. The nonlinear susceptibilities χ(3)(—3ω,ω,ω,ω) of colloidal metals, fullerenes, and dye vapours are measured by the picosecond THG method, and the effect of self-action on THG in these media is analysed.

Third harmonic generation of laser radiation in Fe- and Zn-doped polyvinylpyrrolidone

The results of third-order nonlinear susceptibilities studies of Fe- and Zn-doped polyvinylpyrrolidone (PVP) aqueous solution in processes of third harmonic generation of Nd:YAG laser radiation are presented. Nonlinear susceptibilities of PVP:Fe and PVP:Zn were calculated to be 5×10-13 esu and 3×10-13 esu respectively. Third harmonic conversion efficiencies in these metallocomplexes were measured to be 8×10-7 and 5×10-7 respectively. The Z-scan method was applied to determine Kerr effect influence on frequency conversion process. The value of nonlinear refractive index of PVP:Fe at the wavelength of λ = 1064 nm was measured to be n2 = - 6.7×10-13 esu.

Second harmonic generation in periodically poled crystals for two types of interaction

Second harmonic generation of laser radiation in periodically poled crystals is considered for two types of interaction simultaneously. The possibility of highly efficient frequency conversion of depolarised laser radiation is demonstrated.