Sinterability studies on K0.5Na0.5NbO3 using laser as energy source

The sinterability of K_0.5Na_0.5NbO₃ (KNN) ceramics by a laser beam has been investigated in the present research. A 100 W CO₂ laser with a beam diameter of 0.6 mm has been used to sinter the KNN specimens prepared on a uniaxial pressing machine. The relations between laser power and thickness of densified layer, crystallographic structures and phase compositions have been studied. A comparison has been made between laser and furnace sintered KNN samples according to the SEM, XRD and XRF results. The possibility of KNN used for the layer-wise laser direct sintering 3D components has been confirmed in this paper.     

Comparison of theory and experiment in electron-beam-controlled CO2 laser oscillators

A four-temperature model describing the electron-beam-controlled CO₂ pulsed laser has been developed and used to study the time evolution of a laser pulse and the influence thereon of experimental parameters. This paper explains the experimental results of two different electron-beam CO₂ pulsed laser systems which have been built in the laboratories at Frascati.     

Photothermal effect contribution on film quality improvement in excimer-laser induced metal CVD

KrF excimer laser induced Cr film deposition from Cr(CO)₆ has been studied. Remarkable film quality dependence on laser intensity suggested the photothermal effect contribution of intensive uv laser pulses in the CVD process. A cw Ar-ion laser light and its second harmonic light were used, to separate photochemical and photothermal effects. As a result, photoinduced surface heating has been found to be very important for obtaining good quality metallic films in KrF laser induced Cr film CVD.     

CO-laser photoacoustic detection of phosgene (COCl2)

Detection of COCl₂, a highly toxic gas in chemical industry, using laser photoacoustic spectroscopy is presented. The spectrophone system used has a broad band LN₂ cooled CW CO laser as a source of radiation, which operates from 4.8–8.4 um in the mid-infrared. Using an extracavity open longitudinal resonant cell, absorption signals to about 30 CO laser lines in the 5.45 um region could be observed. detection sensitivity has been estimated to be ppb order.This work has been supported by the NSFC     

CO2 laser assisted removal of UO2 and ThO2 particulates from metal surface

Pulsed laser assisted removal of uranium dioxide and thorium dioxide particulates from stainless steel surface have been studied using a TEA CO₂ laser. Decontamination efficiency is measured as a function of laser fluence and number of pulses. Threshold fluence for the removal of UO₂ particulates has been found to be lower than that required for the removal ThO₂ particulates. Usage of a ZnSe substrate, that is transparent to the laser wavelength used here, enabled us to decouple the cleaning effect arising out of absorption in the particulates from that in the substrate and has contributed towards understanding the mechanism responsible for cleaning. The experimental observations are also corroborated by simple theoretical calculations.     

Discovery and characterization of optically pumped far-infrared laser emissions using laser magnetic resonance spectroscopy

A laser magnetic resonance spectrometer has been used to discover and subsequently measure a far-infrared laser emission: the 166.6-micron line of CH₂F₂, optically pumped by the 9P24 CO₂ laser. By recording spectra for the NH radical, the frequency of this laser emission has been determined to be 1799950±13 MHz. Spectra for the NH radical were also recorded with two other far-infrared laser emissions: the 160.4-micron line of N₂H₄ (9P46 CO₂ pump) and the 328.6-micron line of ¹³CH₃OH (9P12 CO₂ pump). From the NH spectra, a discrepancy of 2.1 GHz with the previously measured laser frequency was identified for the 160.4-micron line. A three-laser heterodyne system was then used to remeasure the frequency to be 1868475.5±0.5 MHz. The NH spectra were also used to determine the frequency for the 328.6-micron line to be 912366±7 MHz, in agreement with the value previously calculated from the Rydberg–Ritz combination principle. PACS 07.57.Hm; 32.60.+i; 42.62.Eh     

CH<Subscript>3</Subscript>OH optically pumped by a <Superscript>13</Superscript>CO<Subscript>2</Subscript> laser: new laser lines and assignments

We report 12 new THz (far-infrared) laser lines from methanol (CH₃OH), ranging from 58.1 μm (5.2 THz) to 624.6 μm (0.5 THz). A ¹³CO₂ laser of wide tunability (110 MHz) has been used for optical pumping, allowing access to previously unexplored spectral regions. Optoacoustic absorption spectra were used as a guide to search for new THz laser lines, which have been characterized in wavelength, polarization, offset, relative intensity, and optimum operation pressure. For 20 laser lines previously observed, we have measured the absorption offset with respect to the ¹³CO₂ laser line center. PACS 33.20.Ea; 33.20.Vq; 33.80.-b     

Isotope separation of some rare-earth elements by two step photoionization

The experimental results of the laser isotope separation (LIS) of europium, samarium and gadolinium atoms by two step selective photoionization are reported. The atom vapour of Eu, Sm, Gd atoms has been produced by the heating of a crucible containing the metal. A dye laser has been used as a selective exciter of the atoms. For the photoionization N₂-laser or mercury lamp have been used.     

Frequencies of cw FIR laser lines for use in laser magnetic resonance spectroscopy

A transversely pumped far-infrared laser cavity has been used to discover two optically pumped laser lines: the 357.7 μm line from H₂C=CF₂ and the 242.3 μm line from CH₃OH. Using heterodyne techniques, the frequencies of fourteen far-infrared laser emissions have been measured, six for the first time. PACS  07.57.Hm; 42.55.Lt; 42.62.Eh     

A simple extended cavity diode laser for spectroscopy around 640 nm

We report on an extended cavity diode laser for operation near 640 nm. The laser is continuously tunable in 10 GHz ranges with a maximum output power of 3 mW. The laser system has been constructed using off-the-shelf optoelectronic components and easily machinable mechanical parts. The constructed system has been used to study the saturated absorption of the closed 1s₅–2p₉ neon transition in a radio-frequency discharge that can be maintained at neon pressures down to 10⁻² Pa.     

Infrared-microwave double resonance as an aid in assignment of optically pumped submillimetre laser lines: CH2CF2, CH2F2, and CH3OH

Infrared-microwave double resonance has been used to confirm recent assignments of optically pumped submillimeter wave laser lines in CH₂CF₂ and CH₃OH, as well as a tentative assignment of a line in CF₂H₂. Intracavity double resonance signals have also been obtained in CF₂CH₂ using a circular copper waveguide laser.     

Short-wavelength far-infrared laser cavity yielding new laser emissions in CD3OH

A significantly improved far-infrared laser has been used to generate optically pumped laser emissions from 26 to 150 μm for CD₃OH. Using an X–V-pumping geometry, several new laser emissions have been found for CD₃OH. In addition, an increase in power, by factors from 10 to 1000, for many of the previously known shorter-wavelength laser lines, below 100 μm, has been observed. Frequency measurements for several lines have also been performed and have been reported to a fractional uncertainty up to ±2×10^-7, permitting the spectroscopic assignment of the laser transition. One of the frequency-measured lines, 44.256 μm observed using the 10R34 pump, has confirmed the assignment of the previously reported FIR emission (n,K;J)=(1,7;20)?(0,8;20)A in the ground vibrational state. Received: 26 October 2000 / Published online: 7 February 2001     

Use of a beam expanding telescope in a grating-tuned waveguide CO2 laser

A Galilean telescope is used as a beam expander in a grating tuned CO₂ waveguide laser to improve line selection while minimizing cavity length to maximise the frequency tuning range. The laser has been used in optoacoustic measurements of saturation of absorption on the transition pumping the 891 m CH₂CF₂ laser.     

Line shape analysis for Zeeman modulation spectroscopy

The technique of Zeeman modulation spectroscopy has been applied to the nitric oxide fundamental in order to compare the observed line shapes and intensities with theory. A predicted change of the sign of theg _J factor at high rotational states has been verified experimentally. The tunable laser source used in the experiment was a spin-flip Raman laser.     

Interaction of CO2 laser radiation with glasses

An illustration of an interaction of pulsed multimode TEA CO₂ laser radiation, through or without a mask, as well as of a laser scanning process of a frequency Q-modulated cw CO₂ laser beam on glass surfaces has been shown. As an object of investigation glass articles with composition as a standard industrial potassium-boron silicate glass, we have used. A complex of investigations shows that the laser treatment leads to qualitative constant changes (well defined peeling structure) depending on the time surface treatment, defocusing and the pulse length of the laser output.     

Resonant light absorption by the ordered structures of ions stored in a trap

Far-infrared laser action has been demonstrated in three previously unknown laser media. The substances used were: propargyl fluoride, 15-N cyanogen fluoride, and hydroxylamine. Assignments of the molecular transitions giving rise to the observed laser lines were made for the latter two compounds.New FIR laser lines were also observed with two substances, vinyl chloride and vinyl fluoride, which were already known as laser media by pumping with isotopic CO₂ and N₂O laser lines.The wavelengths of a total of 26 new FIR laser lines were determined together with the threshold pump power and an indication of the relative line strengths.     

Laser welding of steels for power plant

Many welding applications in CEGB power plant involve components with wall thicknesses in the range 2–10 mm. Therefore, an investigation into the feasibility of laser welding types 316, 310 and DUCOL W30 steels in 6 mm thick plate has been made, the materials being typical of those used in CEGB power plant.The welds were made using the high power, transverse flow, CO₂ laser based at UKAEA Culham Laboratory. The laser welding process used has been compared with TIG (tungsten inert gas), plasma and electron beam using capital cost, power requirement, ease of handling and distortion in workpieces as the criteria for comparison. Possible applications of laser welding to power plant manufacture are discussed.     

Nitrogen-laser-pumped single-mode dye laser

Single-mode operation of a N₂-laser-pumped'dye laser has been obtained in a short laser cavity consisting of a diffraction grating used near grazing incidence and an uncoated resonant reflector. The dye laser pulse has a spectral linewidth of 420±30 MHz and a pulse width of 1.1±0.1 ns, giving a time-bandwidth of 0.46±0.07 close to the Fourier transform limit for Gaussian pulse.     

A comparative study of gadolinium gallium garnet growth by femtosecond and nanosecond pulsed laser deposition

The growth of epitaxial Nd:Gd₃Ga₅O₁₂ (GGG) on Y₃Al₅O₁₂ (YAG) by femtosecond pulsed laser deposition is reported. We have used a Ti:sapphire laser at a wavelength of 800 nm and pulse length of 130 fs, operating at a repetition rate of 1 kHz. The film properties have been studied systematically as a function of the deposition parameters of laser fluence, spot-size, oxygen pressure, target-substrate distance and temperature. Scanning electron microscopy, atomic force microscopy and X-ray diffractometry were used to characterise the surface structure and crystallinity of the films. X-ray diffraction analysis shows that epitaxial growth has occurred. A comparison between the ion velocities produced by nanosecond and femtosecond laser ablation of the GGG target material has been investigated by the Langmuir probe technique. The results indicate a large difference in the plasma characteristics between femtosecond and nanosecond ablation, with ion velocities up to eight times faster observed in the femtosecond case.     

Spectral dynamics of narrow-band F<Subscript>2</Subscript> laser for optical lithography

We describe the spectral dynamics of a line-narrowed F ₂ laser, based on numerical simulation by a newly developed simulation code. The results were compared with the experimental results and it was found that the code could predict well the performance of a line-narrowed operation of the F ₂ laser. The code was also used to obtain a guideline for the optimized operation of an injection-seeded F ₂ laser system. In addition, a new spectral narrowing technique for the F ₂ laser has been proposed and its effectiveness was evaluated by the simulation code.