Frequency Conversion Of Laser Radiation Research Articles

Atomic versus molecular plasmas for frequency conversion of laser radiation: stronger harmonics, larger cutoffs, better stability, resonance, and quasi-phase-matching enhancement

Atomic versus molecular plasmas for frequency conversion of laser radiation: stronger harmonics, larger cutoffs, better stability, resonance, and quasi-phase-matching enhancement

Temperature dependence of the properties of the Li0.81Ag0.19InSe2 nonlinear crystal

The factors that determine the prospects of a crystal for frequency conversion of laser radiation in a wide range to the mid and far infrared (IR) ranges are nonlinear parameters and laser damage threshold (LDT). The latter is determined by the band gap and thermophysical characteristics. This work was devoted to studying the features of the structure change of the Li0.81Ag0.19InSe2 crystal in the temperature range 90–490 K. The temperature dependences of the thermal expansion coefficients, dispersion and optical characteristics in this range were studied. A relationship between the temperature change in the structure and other parameters has been established. In Li0.81Ag0.19InSe2 crystals, pyroluminescence was observed during heating or cooling in the range of 100–300 K, which indicates the crystal is attributed to pyroelectrics. The dispersion characteristics (nx, ny and nz) for wavelengths of 2 and 7 μm were studied, the values of birefringence Δn (nz - nx) were calculated in the temperature range 300–500 K. The detected fluctuations of Δn in the temperature range from 300 to 478 K may be associated with structural changes.

Functional possibilities of nonlinear crystals for laser frequency conversion: biaxial crystals

We report the method and results of a complex analysis of phase-matching and nonlinear properties for biaxial crystals of all point groups of symmetry, which determine their functional possibilities in solving various problems of nonlinear frequency conversion of laser radiation.

Effect of doping on the mechanical properties of nonlinear GaSe crystals

The effect of doping with sulfur, indium, tellurium, aluminum, erbium, and silver on the mechanical properties of nonlinear GaSe crystals grown by a modified Bridgman method with the rotation of a thermal field is studied. GaSe:S crystals have the best optical properties and GaSe:Al crystals have the highest microhardness. Under identical experimental conditions, we revealed an additive influence of double doping on the properties of GaSe: the crystals doped with sulfur and aluminum demonstrate the maximum efficiency of laser radiation frequency conversion and the maximum hardness. The increased hardness is supported by the appearing ability of the crystals to undergo cracking under the action of high-intensity radiation, which is characteristic of glass.

Functional possibilities of nonlinear crystals for frequency conversion: uniaxial crystals

The method and results of the analysis of phase-matching and nonlinear properties for all point groups of symmetry of uniaxial crystals that determine their functional possibilities for solving various problems of nonlinear frequency conversion of laser radiation are presented.

Ultra-broadband hybrid infrared laser system

A hybrid IR laser system consisting of molecular gas lasers with frequency conversion of laser radiation in a solid-state converter (nonlinear crystal) was developed. One of these gas lasers is a carbon monoxide laser operating in multi-line or single-line mode. Another one is a carbon dioxide laser operating in multi-line mode. The two lasers operate under Q-switching with a joint rotating mirror. Due to sum- and difference-frequency generation in nonlinear crystals, the laser system emits within wavelength range from 2.5 to 16.6μm. The laser system emitting radiation over such an extremely wide wavelength range (2.7octaves) is of interest for remote sensing and other applications connected with laser beam propagation in the atmosphere.

Broadband frequency conversion of laser radiation in ZnGeP2 crystal

The phase matching conditions in the ZnGeP2 crystal are calculated and analyzed from the viewpoint of broadband frequency conversion of mid-IR radiation. The frequency conversion of Cr:ZnS laser radiation in the ZnGeP2 crystal is calculated. The results show the possibility of developing a broadband laser source whose spectrum spans a wavelength range of 3.2–9.5 µm.

Sub-femtosecond hard X-ray radiation generated by electron bunches ejected from water jet

AbstractA new two-step approach for frequency conversion of laser radiation towards hard X-rays is developed and examined experimentally. Fast electrons are produced in a form of thin jets at the first stage, as an intense femtosecond laser pulses impinges on a micrometer water target. In the second stage the accelerated electrons hit a secondary metal target and generate characteristic K-shell radiation with a duration down to sub-femtosecond. It is shown that counter propagating laser radiation experiences very strong up-shift with up to 6 × 103 times of fundamental frequency by reflection from the electron jets.

Laser radiation frequency conversion in carbon- and cluster-containing plasma plumes under conditions of single and two-color pumping by pulses with a 10-Hz repetition rate

This work reviews a series of investigations of different plasma plumes using single- and two-color laser systems that emit femtosecond pulses with a 10-Hz repetition rate. Results of investigation of the resonant enhancement of harmonics in tin plasma with the use of two types of pumps are analyzed, and it is shown that the tuning of the wavelengths of harmonics to ion-resonance levels plays an important role in increasing the conversion efficiency to high-order harmonics of the radiation to be converted. Investigations of different carbon-containing plasma media (carbon nanotubes, graphite, carbon aerogel, etc.) exhibit attractive properties of the nonlinear medium of this type for efficient generation of high-order harmonics. The results of the first experiments on the use of nanoparticles produced directly in the course of laser ablation of metals for increasing the efficiency of harmonics generated in this cluster-containing medium are analyzed. It is shown that new approaches realized in these investigations give hope that the nonlinear optical response of plasma media in the far-ultraviolet range can be further increased.

New Approaches in Frequency Conversion of Laser Radiation in Plasma Plumes

Recent studies of plasma harmonic generation are reviewed. We show the advances of this technique for generation of coherent ultrashort pulses in the extreme ultraviolet range. Among the achievements highlighted in this review are the comparative experimental and theoretical studies of high-order harmonic generation in silver plasma, isolated subfemtosecond pulse generation in Mn plasma ablation, stable generation of high-order harmonics of femtosecond laser radiation from laser produced plasma plumes at 1 kHz pulse repetition rate, and high-order harmonic generation in fullerenes using few- and multi-cycle pulses of different wavelengths. We show that new developments of plasma harmonic studies can lead to the creation of an attractive field of laser ablation induced high-order harmonic generation spectroscopy.

Strong Field-Induced Frequency Conversion of Laser Radiation in Plasma Plumes: Recent Achievements

New findings in plasma harmonics studies using strong laser fields are reviewed. We discuss recent achievements in the growth of the efficiency of coherent extreme ultraviolet (XUV) radiation sources based on frequency conversion of the ultrashort pulses in the laser-produced plasmas, which allowed for the spectral and structural studies of matter through the high-order harmonic generation (HHG) spectroscopy. These studies showed that plasma HHG can open new opportunities in many unexpected areas of laser-matter interaction. Besides being considered as an alternative method for generation of coherent XUV radiation, it can be used as a powerful tool for various spectroscopic and analytical applications.

Crystal growth, structural, optical, spectral and thermal studies of tris( l-phenylalanine) l-phenylalaninium nitrate: A new organic nonlinear optical material

Tris( l-phenylalanine) l-phenylalaninium nitrate, C 9H 12NO 2 +·NO 3 −·3C 9H 11NO 2 (TPLPN), a new organic nonlinear optical material was grown from aqueous solution by slow evaporation solution growth at room temperature. The grown crystals were subjected to powder X-ray diffraction and single crystal X-ray diffraction studies to confirm the crystalline nature and crystal structure. The modes of vibration of different molecular groups present in TPLPN have been identified by FTIR spectral analysis. The presence of hydrogen and carbon in the grown crystal were confirmed by using proton and carbon nuclear magnetic resonance (NMR) spectral analyses. The optical transmission spectral study establishes good transmitting ability of the crystal in the entire visible region. The thermogravimetric (TG) and differential thermal analyses (DTA) were carried out to understand the thermal stability of the sample. The nonlinear optical property of the compound observed using Kurtz powder second harmonic generation test assets the suitability of the grown material for the frequency conversion of laser radiation of Nd:YAG.

Generation of higher harmonics of femtosecond radiation in clusters

The frequency conversion of laser radiation in cluster media is studied by the method of laser ablation of surfaces containing different nanoparticles (Cr2O3, In2O3, Ag, Sn, Au, and Cu). Using plasma that contains In2O3 nanoparticles as an example, it is shown that the resonant amplification of certain harmonics in the plateau-like distribution of harmonics, which is characteristic of the ablation of certain solid targets, is considerably modified in the case of targets that contain cluster formations. An increase in the conversion efficiency to harmonics in nanoparticle-containing media is discussed. In order to determine optimal characteristics of laser plasma with nanoparticles, their morphology is studied before and after laser ablation.

Generation of higher-order harmonics of chirped radiation from a titanium-sapphire laser in plasma generated by pulses of different durations

The frequency conversion of laser radiation in plasma created by pulses of different durations under conditions of the chirp variation of the radiation to be converted is investigated. It is shown that the chirp variation of the laser pulse during the generation of higher-order radiation harmonics of the femtosecond laser leads to a considerable change in the brightness, wavelength shift, and maximal order of generated harmonics. The long-and short-wavelength shifts of harmonics observed in these studies are attributed to the manifestation of a considerable concentration of free charge carriers in the plasma, as well as the self-modulation of the laser pulse. The generation of plasma by pulses whose durations vary from 160 fs to 20 ns is considered and it is shown that the generation efficiency of harmonics depends to a greater extent on the energy of the heating prepulse than on its intensity on the surface of a target to be ablated. The effect that the atomic number of the target has on the formation of optimal plasma at different delays between the heating prepulse and the femtosecond pulse to be converted is discussed.

Higher harmonic generation in laser plasma upon interaction of femtosecond laser pulses with doubly and singly charged ions under conditions of resonance frequency conversion of laser radiation

The higher harmonic generation (HHG) in plasmas formed on the surface of different solid targets (Pb, Ag, Ge, In, Au, Cr, Pt, V, Mn, Ga, Bi, Sb, Cu, Al, Ca, and Sn) by laser ablation is studied. The possibility of HHG upon interaction of femtosecond radiation with doubly charged ions is studied on the example of Mn plasma. This process allowed generation of higher harmonics of up to the 101st order. The results of investigation of individual enhanced harmonics in Sn, Sb, In, and Cr plasmas are presented. Comparison of the conditions of HHG in weakly and strongly excited plasmas showed that the latter is preferable for efficient frequency conversion. It is demonstrated that the use of laser plasma spectroscopy with high time resolution allows one to determine the optimal conditions for generation of harmonics with a plateaulike distribution in the far-UV spectral region.

A new method of calculating the efficiency of nonlinear frequency conversion of laser radiation with focused beams

This paper proposes a theoretical model of the nonlinear frequency conversion of laser radiation in a nonlinear crystal (NC) in which the model makes it possible to carry out calculations both in the absence of focusing and in the case of various geometries of the focusing system: spherical or cylindrical. The model is based on the numerical solution of a system of coupled differential equations that describe the nonlinear conversion process, combined with a homogeneous wave equation, by means of which the propagation of focused radiation in the NC is calculated.

Efficient dye jet laser pumped by CuBr vapor laser

Possibilities for efficient dye jet laser pumping by CuBr vapor laser are investigated. 8×10 -3 M/1 solution of R590 dye in ethylene glycol is found most suitable for CuBr laser radiation frequency conversion. After experimenting with different dye laser cavity configuration 63% conversion efficiency and tunability in a broad spectral range are achieved.

Influence of color centers on the optical properties of KTP crystals and on the efficiency of the laser radiation frequency conversion in these crystals

Color centers were observed in nonlinear KTiOPO4 (KTP) crystals under conditions of second harmonic generation (SHG) of λ = 1.064 μm neodymium laser radiation at power densities > 100 MW/cm2. The additional absorption at the SHG wavelength (λ = 0.532 μm) reduced the efficiency of conversion of the laser radiation frequency in KTP crystals and their optical strength at the second harmonic wavelength.

Gamma: an instrument for frequency conversion of laser radiation and modification of laser pulse duration

Gamma: an instrument for frequency conversion of laser radiation and modification of laser pulse duration

Use of "skew" elements for frequency conversion of laser radiation

The use of skew crystal elements with the surfaces parallel to a natural growth face for conversion of laser radiation frequency (oee phase matching) made it possible to increase considerably the utilization of such crystals without loss of the conversion efficiency. Skew elements were used to generate the second harmonic of neodymium laser radiation and the conversion characteristics were determined for elements used in frequency doubling and tripling.