Single longitudinal mode pulse from a TEA CO<Subscript>2</Subscript> laser by using a three-mirror resonator with a Fabry–Pérot etalon

We present a single longitudinal mode (SLM) TEA CO₂ laser oscillation by using a three-mirror resonator with a Fabry–Pérot etalon. The etalon was inserted in the optical path taken out from the main resonator of the CO₂ laser for protecting the etalon from damage on the surface. A modified numerical model of the three- mirror resonator was investigated for design the laser. SLM pulse from the TEA CO₂ laser was achieved, and the experimentally measure values were found to have good agreement with the numerical model. The maximum pulse energy of reliable SLM emission is obtained in excess of 200 mJ at 9.57 μm. The reliability of producing SLM pulses was higher than 90%, and there was no damage on the etalon PACS  42.55.Lt; 42.60.Fc     

Energy efficiency of femtosecond laser ablation of polymer materials

We present the results of an experimental study of the ablation spectral energy thresholds for a number of polymer materials ((C₂F₄) _n , (CH₂O) _n ) exposed to femtosecond (τ_0.5 ~ 45–70 fs) laser pulses (λ ~ 266, 400, 800 nm) under atmospheric conditions and under vacuum (p ~ 10–2 Pa). We have analyzed the energy thresholds and the efficiency of optical, thermophysical, and gasdynamic processes in laser ablation vs. the laser pulse duration and photon energy.     

Intracavity parametric conversion of radiation from a pulsed Nd:YVO<Subscript>4</Subscript> laser with high-power diode pumping

We have achieved intracavity parametric conversion of the radiation from a laser based on Nd:YVO₄ with high-power diode pumping. An LiF^2- crystal was used as the passive Q-switch for the Nd:YVO₄ laser. We have shown that by using an active element in the master laser with a passive region, we can form pulsed laser beams at a wavelength of 1.57 μm with peak power 3.2 kW and repetition rates up to 80 kHz, with beam quality parameter 1.4–1.8. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 5–8, January–February, 2006.     

Optical transmission of ceramic shielding blocks made from Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

We have studied the transmission of bulk Al₂O₃ ceramic used as heat shields for the working chamber of a turbine. We have established that radiation scattered from such an object has a pronounced speckle structure, while the scattering indicatrix is the same as the indicatrix for an ideal scatterer. We show that existing highpower semiconductor laser sources make it possible to penetrate sufficiently deeply into such materials, and the small transmission coefficient is not the limiting factor for development of optical methods for inspecting the quality of ceramic shielding blocks. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 237–240, March–April, 2007.     

Temperature variation of the optical absorption edge for ammonium aluminum alum

We have studied the absorption spectra of NH₄Al(SO₄)₂·12H₂O crystal hydrates in the visible region of the spectrum, near the low-temperature phase transition at T_c = 76 K. We have shown that the absorption edge in these materials has an exponential shape, following the empirical Urbach’s rule as a result of exciton-phonon interaction. The relatively strong exciton-phonon interaction is associated with a band formed by self-localized (self-trapped) excitons. The experimental data obtained support the presence of a phase transition in the studied ammonium alum at 76 K. We have shown that ammonium aluminum sulfate dodecahydrate crystals are promising materials for fabricating laser frequency converters. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 258–262, March–April, 2007.     

Optimization of laser hole drilling process on thick gold spherical hohlraums for intense X-ray generation

Hohlraums of high-Z materials are used as soft X-ray sources to study indirect drive fusion, equation of state of materials etc. Here, we describe a method to develop spherical gold hohlraums of large wall thickness (∼70–80 μm) on which laser entrance and diagnostics holes are drilled using a 10 Hz Nd:YLF laser. Holes of different diameters have been drilled with lenses of different focal lengths. The back wall of the hohlraum is protected from the damage by shutting off the laser at pre-determined hole drilling time.     

Sticking efficiency of nanoparticles in high-velocity collisions with various target materials

In order to find reliable collector surfaces for the Mesospheric Aerosol – Genesis, Interaction and Composition (MAGIC) sounding rocket experiment, intended to collect atmospheric nanoparticles, the sticking efficiency of nanoparticles was measured on several targets of different materials. The nanoparticles were generated by a molecular beam apparatus in Jena, Germany, by laser ablation (Al₂O₃ particles, diameter 5–50 nm) and by laser pyrolysis (carbon particles, diameter 10–20 nm). In a vacuum environment (>10⁻⁵ mbar) the particles condensed from the gas phase, formed a particle beam, and were accelerated to ∼ ∼1 km/s. The sticking efficiency on the target materials carbon, gold and grease was measured by a microbalance. Results demonstrate moderate to high sticking probabilities. Thus, the capture and retrieval of atmospheric nanoparticles was found to be quantitatively feasible.     

Azimuthal dependence of the two-photon absorption coefficient for CdP2 crystals with tetragonal syngony

We studied the two-photon absorption coefficient (β) for cadmium diphosphide (CdP₂) single crystals in the tetragonal modification vs. the polarization azimuth (φ) of the incident light for intensities close to the optical breakdown (or optical damage) threshold for the crystal (11 MW/cm²). We have established that the value of β_max = 0.16 cm/MW is reached for φ = 0, i.e., for the ordinary wave. At the lasing frequency of a ruby laser, β_⊥/β_|| = 2.13, which suggests anisotropy of the two-photon absorption in the studied crystals. These dependences are needed for design and fabrication of quantum electronics and nonlinear optics elements whose operation is based on the use of the two-photon absorption effect for high radiation fluxes. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 117–121, January–February, 2009.     

Lasing action of rhodamine B in polyacrylic acid films

 Rhodamine B (Rh-B) has been embedded in PolyAcrylic acid (PAA) films. The materials are studied for the laser action with nitrogen laser excitation. The lasing efficiency of Rh-B/PAA films is comparable to that of rhodamine 6G in methanol. There is a 50% reduction in the laser intensity of the films with 2600 pulses from the N₂ laser (2 Hz). The photostability of these materials is far superior to that of other polymeric materials and is comparable to that of sol–gel materials. Received: 22 May 1996 /Revised version: 10 July 1996     

Near IR laser light visualizators using nonlinear GaSe and other layered crystallites

Two methods of preparation of the devices for visualization of pulsed and continuous near-IR (near infrared) are described and the results of conversion of pulsed and continuous IR (800–1360 nm) laser radiation into the visible range of spectra (400–680 nm) by using a transparent substrate covered with the particles (including nanoparticles) of effective nonlinear materials of GaSe _x S_{1 − x} (0.2 ≤ x ≤ 0.8) are presented. Converted light can be detected in transmission or reflection geometry as a visible spot corresponding to the real size of the incident laser beam. Developed device structures can be used for checking if the laser is working or not, for optical adjustment, for visualization of distribution of laser radiation over the cross of the beam and for investigation of the content of the laser radiation. Low energy (power density) limit for visualization of the IR laser pulses with 2–3 ps duration for these device structures are: between 4.6–2.1 μJ (3 × 10⁻⁴−1 × 10⁻⁴ W/cm²) at 1200 nm; between 8.4–2.6 μJ (4.7 × 10⁻⁴−1.5 × 10⁻⁴ W/cm²) at 1300 nm; between 14.4–8.1 μJ (8.2 × 10⁻⁴–4.6 × 10⁻⁴ W/cm²) at 1360 nm. Threshold damage density is more than 10 MW/cm² at λ = 1060 nm, pulse duration τ = 35 ps. The results are compared with commercially existing laser light visualizators.     

InTaO<Subscript>4</Subscript>-based nanostructures synthesized by reactive pulsed laser ablation

Nanostructured Ni-doped indium–tantalum–oxides (InTaO₄) were synthesized by a reactive pulsed laser ablation process, aiming at the final goal of direct splitting of water under visible sunbeam irradiation. The third harmonics beam of a Nd:YAG laser was focused onto a sintered In_0.9Ni_0.1TaO_4−δ target in pure oxygen background gases (0.05–1.00 Torr). Increasing the oxygen gas pressure, via thin films having nanometer-sized strong morphologies, single-crystalline nanoparticles were synthesized in the reactive vapor phases. The nanostructured deposited materials have the monoclinic layered wolframite-type structure of bulk InTaO₄, without oxygen deficiency.     

Pattern structures fabricated on ZnS–SiO2/AgO x /ZnS–SiO2 thin film structure by laser direct writing technology

In this work, we used the multilayered ZnS–SiO₂/AgO _x /ZnS–SiO₂ films as the laser direct writing materials, and pattern structures with different shapes and sizes were directly written with green laser (λ=488 nm). Compared with traditional photoresist materials, the pattern structures can be directly formed in this film structures without developing and etching procedures and also can be directly written by very low laser power. By tuning the laser parameters precisely, pattern structures with different sizes and shapes could be obtained as well. The analysis indicates that the formation mechanism of the pattern structure is mainly due to the volume expansion caused by AgO _x decomposition into silver particles and oxygen. The oxygen applies pressure to the ZnS–SiO₂ layer and makes a hollow shell under the film. The aspect ratios of the patterns rapidly increase from the minimum of 0.012 in laser power of 3.0 mW to the maximum of 0.201 in laser power of 5.0 mW. The thermal stability of the patterns was also qualitatively studied.     

Structural transformations of polysaccharides exposed to CO2-laser radiation

We have used IR spectroscopy to study conformational transformations of polysaccharide macromolecules (dextran, pullulan, amylose, and microcrystalline cellulose) and changes in their structural ordering when exposed to cw emission of a CO₂ laser. We have established that the structures of conformationally labile polysaccharides are the most sensitive to laser radiation. The effect of laser treatment is greatest for lower molecular weight polymers. We have observed for the first time changes in the conformational states of dextran macromolecules in the direction of an increase in the structural ordering when exposed to emission from a CO₂ laser. This quite different from purely thermal treatment, where disordering of the polysaccharides structure occurs. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 164–169, March–April, 2006.     

Determination of reference values for optical characteristics in multiwavelength optical detection and ranging (lidar) measurements of atmospheric extinction coefficients

We have studied multiple regressions between the spectral aerosol extinction coefficient ε, backscatter indicatrix g_π, and light-scattering coefficients β_θ at angles of θ = 1–180°, which we used to select the optimal scattering angle for determining the extinction coefficient at the wavelengths 0.350, 0.532, and 1.060 μm. We have estimated the errors in determination of the values of ε and g_π at the given wavelengths for different atmospheric situations with different meteorological parameters. We have shown that it is possible to use the spectral β_θ values at a 33° angle to determine the reference values for ε(λ) and g_π(λ) at λ = 0.350, 0.532, and 1.060 μm in laser detection and ranging (lidar) measurements, and we give examples of recovering the vertical profiles of ε in a slightly turbid atmosphere from the results of simultaneous multiwavelength lidar and nephelometric measurements. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 767–772, November–December, 2007.     

Optical properties of films of the ternary compound CuIn<Subscript>3</Subscript>Se<Subscript>5</Subscript>

We have used the laser vaporization method to obtain films of the ternary compound CuIn₃Se₅ and have studied the composition and structure of the films obtained. We have determined the energy and nature of the optical transitions for the indicated compound from the transmission spectra in the region of the intrinsic absorption edge. We have calculated the valence-band crystal-field (Δ_CF) and spin-orbit (Δ_SO) splitting energies according to Hopfield’s quasicubic model for the ternary compound CuIn₃Se₅. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 82–85, January–February, 2007.     

Stimulated Raman conversion of radiation from a YAG:Nd laser with wavelengths of 1.319, 1.338, and 1.357 µm in a barium nitrate crystal

We have studied stimulated Raman (SRS) conversion to the first Stokes component of multimode (M₂ = 8) radiation from a YAG:Nd laser with lasing wavelengths of 1.319 μm, 1.338 μm, and 1.357 μm in a barium nitrate crystal. We have obtained pulses of converted radiation with energies up to 120 mJ. We have achieved conversion efficiencies greater than 40% for each of the three Raman laser wavelengths of 1.530 μm, 1.556 μm, and 1.582 μm with divergence of the beams of converted radiation close to the diffraction-limited value (M₂ < 1.5). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 330–334, May–June, 2006.     

Photoinduced optical activity of C<Subscript>70</Subscript> fullerene in organic solvents

We have experimentally studied for the first time the effect of photoinduced rotation of the plane of polarization for pulsed laser radiation in solutions of C₇₀ fullerene in organic solvents and their mixtures. We have shown that the effect is observed for elliptical polarization of the laser radiation and is absent for linear polarization. We present the results of a study of the nonlinear optical characteristics of the C₇₀ solutions. We discuss the physical mechanisms by which nonlinear gyrotropy is induced in solutions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 93–99, January–February, 2009.     

Tunable optical parametric oscillator based on a KTP crystal,pumped by a pulsed Ti<Superscript>3+</Superscript>:Al<Subscript>2</Subscript>O<Subscript>3</Subscript> laser

We present the characteristics of an optical parametric oscillator based on a KTP crystal, pumped with noncritical phase matching by a pulsed Ti³⁺:Al₂O₃ laser, tunable in the range 677–970 nm. Tunable generation of signal and idler waves is obtained in the ranges 1030–1390 nm and 2690–3050 nm respectively. The efficiency of conversion of the pump to the signal wave is ≈23%, which for pulses of duration ≈8 nsec ensures an energy in the range 1.0–11.5 mJ. The width of the emission spectrum for the signal wave is within the range 0.8–1.8 nm and is predominantly determined by the linewidth of the Ti³⁺:Al₂O₃ pump laser. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 351–356, May–June, 2007.     

Fabrication of polaritonic structures in LiNbO<Subscript>3</Subscript> and LiTaO<Subscript>3</Subscript> using femtosecond laser machining

Fabrication of patterned materials in ferroelectric LiNbO₃ and LiTaO₃ crystals using femtosecond laser micromachining is presented and discussed. Damage feature sizes in the 10–100 μm range were achieved using 800-nm, 50-fs (FWHM) ultra-fast laser pulses with energies ranging from 10 μJ up to 350 μJ. Fabrication of polaritonic devices such as waveguides, resonators, focusing reflectors, diffractive and dispersive elements, photonic band gap materials, and other microstructures is demonstrated. PACS 77.84.Dy; 42.62.Cf; 71.36.+c     

Picosecond laser ablation of SiO2 layers on silicon substrates

In this work, we report on laser ablation of thermally grown SiO₂ layers from silicon wafer substrates, employing an 8–9 ps laser, at 1064 (IR), 532 (VIS) and 355 nm (UV) wavelengths. High-intensity short-pulse laser radiation allows direct absorption in materials with bandgaps higher than the photon energy. However, our experiments show that in the intensity range of our laser pulses (peak intensities of <2×10¹² W/cm²) the removal of the SiO₂ layer from silicon wafers does not occur by direct absorption in the SiO₂ layer. Instead, we find that the layer is removed by a “lift off” mechanism, actuated by the melting and vaporisation of the absorbing silicon substrate. Furthermore, we find that exceeding the Si melting threshold is not sufficient to remove the SiO₂ layer. A second threshold exists for breaking of the layer caused by sufficient vapour pressure. For SiO₂ layer ablation, we determine layer thickness dependent minimum fluences of 0.7–1.2 J/cm² for IR, 0.1–0.35 J/cm² for VIS and 0.2–0.4 J/cm² for UV wavelength. After correcting the fluences by the reflected laser power, we show that, in contrast to the melting threshold, the threshold for breaking the layer depends on the SiO₂ thickness.