All-solid-state tunable DCM dye laser pumped by a diode-pumped Nd:YAG laser

Lasing is observed near 620 nm in a DCM dye doped TiO(2)-content organically modified silicate (ORMOSIL) pumped by frequency-doubled radiation from a diode-pumped Q-switched Nd:YAG laser. The laser wavelength is tunable over 60 nm. A conversion efficiency of 18% is obtained at its central wavelength of 621 nm. The laser output energy has only a 10% reduction after 27,000 pulses at a pump repetition rate of 30 Hz and a pump intensity of 1 J/cm(2). An all-solid-state, compact, long-lifetime, and tunable dye laser has been demonstrated.     

Highly efficient polymeric dye laser pumped at 1.06 μm

A tunable dye laser using a polyurethane-based active element pumped at 1.06 μm was obtained for the first time. The laser, employing polymethine dye 2696_y, has an energy conversion efficiency of 43% and can be tuned within a Δλ=63 nm wavelength interval.     

High-power HF laser pumped by an electron-beam-initiated chemical nonchain reaction

The development of a high-power HF laser pumped by a chemical nonchain reaction initiated by a radially converging electron beam is reported. A radiation energy of ∼ 115 J with an efficiency of ∼ 8% in terms of deposited energy has been achieved in a mixture with an active volume of ∼ 30 liters. It is shown that because of the high SF₆ density, the total pressure jump in SF₆–H₂(D₂) mixtures caused by the electron beam injection and the chemical reactions is several times smaller than that in the active mixtures of exciplex lasers for the same input energies. This factor considerably facilitates the development of wide-aperture HF and DF lasers with an SF₆ fluorine donor pumped by an electron-beam-initiated chemical nonchain reaction. Pis’ma Zh. Tekh. Fiz. 23, 58–64 (March 12, 997)     

Characteristics of a dye laser amplifier transversely pumped by copper vapor lasers with a two-dimensional calculation model

A two-dimensional rate equation model, taking into consideration the transverse absorption loss of pump laser power, is proposed to evaluate the characteristics of a dye laser amplifier with a large input laser beam diameter pumped by high average power copper vapor lasers. The calculations are in good agreement with the measurements taken with a Rhodamine 6G dye, and the model can be used for evaluation of the dye concentration at any wavelength.     

Single-photon ionization quadrupole mass spectrometry with an electron beam pumped excimer light source

The application of soft ionization methods for mass spectrometry (MS), such as single-photon ionization (SPI) using vacuum ultraviolet (VUV) light, provides powerful analytical instrumentation for real-time on-line monitoring of organic substances in gaseous matrixes. A compact and mobile quadrupole mass spectrometer (QMS) system using a novel electron beam pumped rare gas VUV lamp for SPI has been developed for on-line analysis of organic trace compounds (ppb concentrations). The VUV radiation of the light source is employed for SPI in the ion source of the QMS. The concept of the interfacing of the VUV light source with the QMS is described and the SPI-QMS is characterized. On-line detection limits down to 50 ppb for benzene, toluene, and m-xylene were achieved. The instrument is well suited for continuous measurements of aromatic and aliphatic trace compounds and can therefore be used for on-line monitoring of trace compounds in dynamically fluctuating process gases. First measurements of gas standards, petrochemical samples, and on-line monitoring of automotive exhaust are presented.     

Spectroscopy and laser characteristics of copper-vapor-laser pumped pyrromethene-556 and pyrromethene-567 dye solutions

We measured the basic optical properties of Pyrromethene-567 (P567) and Pyrromethene-556 (P556) dye solutions that are relevant to their application as dye lasers. The fluorescence spectra of methanol solutions show mirror images in relation to the absorption spectra, with Stokes shifts of 29.5 and 37.5 nm, respectively, for the two dyes. The central fluorescence peaks were at 546 and 535 nm, with widths of ~40 and ~50 nm (FWHM). The quantum yields were 97% ? 5% and 78% ? 5% for P567 and P556, respectively. Fluorescence lifetimes of 6.0 ? 0.2 ns were obtained for both dyes in methanol. Laser action, obtained by pumping with the green emission line (510.6 nm) from a copper-vapor laser, was measured in a H?nsch-type cavity. Tunability ranged from 531 to 590 nm for P567 and from 522 to 590 nm for P556. Lasing thresholds were ~0.27 and ~0.16 mJ/pulse, with 25% and 27% slope efficiencies for P567 and P556, respectively. Spectroscopy and lasing were studied in other solvents as well.     

New designs and simulations of a 10-kW average-power longitudinally pumped dye laser amplifier

New designs of a 10-kW average-power longitudinally pumped dye laser amplifier pumped by a copper laser and its operating simulations are presented. The new designs, which use a center-hole mirror, make it possible to pump longitudinally without dichroic mirrors. The simulations take into consideration the time-dependent excited-state absorption of both the laser and the pump beam. Dye laser amplifiers, with an input dye laser average power of 10 kW, are simulated. The simulation results suggest that a better than 50% extraction efficiency can be obtained with two pump beams of more than 1 kW. The results also suggest that an amplified gain of 10 with an extraction efficiency of approximately 50% can be obtained with the double-pass amplifier.     

Laser-machining experiment with an excimer laser and a kinoform

We have used a kinoform to increase the beam-power utilization in an excimer-laser-machining experiment. The kinoform creates the pattern to be machined. Thus less power is wasted on the blocking parts of a shadow mask. To achieve as smooth an intensity profile as possible, the kinoform was also used together with a microlens-array beam homogenizer. We discuss the intensity distributions of the patterns created by the kinoform with and without the beam homogenizer as well as the design of the kinoform and the homogenizer, with emphasis on the relation to the coherence properties of the laser beam.     

Surface treatment for adhesive-bonded joints by excimer laser

In this work a treatment for surface preparation to improve mechanical resistance in adhesive bonding of plastic composites reinforced with fibres and metallic material, has been performed using an excimer laser. The following couplings have been selected to reproduce joints commonly used in the aerospace and automotive industry: CFC (carbon fibre composite) with CFC, CFC with Al 2024T3, Al 99% with Al 99%, GFC (glass fibre composite) with zinc-coated sheet in low carbon steel FeP01. The surfaces have been prepared using an excimer laser, adopting several values of laser parameters. The obtained surfaces have been examined by optical and scanning electron microscope: comparative measures of wetting and roughness have been performed to obtain an accurate characterisation and to select the proper finishes suitable to improve the mechanical resistance of the joints. The results obtained show that laser treatment always improves the final resistance of the joint; notable increases, and no significant surface damages have been highlighted. Better results have been obtained with the Al 99% with Al 99% joints which, with a low number of pulses treatment, have shown an increase of mechanical resistance up to the 70%.     

Copper vapor laser pumped by pulse-periodic high-frequency discharge

We present the results of numerical experiments considering the physical processes specific to the laser based on self-terminating atomic transitions of copper and study of the output characteristics of this laser numerically. The laser is pumped by trains of high-frequency (10?70 MHz) current oscillations with the repetition rate of 2?30 kHz. Inductive-type electrodeless discharge pumping is regarded. The calculations were carried out for a small set of the specified basic parameters providing a way to partially optimize the performance of the laser over its basic output characteristics and to reveal its features. The feasibility of efficient laser pumping by high-frequency discharge is demonstrated. In our numerical experiments the maximum value of the physical efficiency was about 6% and the maximum average laser output power was as high as 174 W. These values were obtained for a discharge chamber with a volume of 1.7 L.     

Nanomechanical properties of silicon surfaces nanostructured by excimer laser

Abstract

Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm^?2. A single-crystal silicon [311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses.     

Photoresonant ionization of gaseous media by excimer laser radiation

An identification is made of twenty five elements whose resonance lines overlap the emission lines of high-power pulsed ultraviolet gas lasers or lie in the immediate vicinity of them, so that the mechanism laser ionization based on resonance saturation (LIBORS) can be used to ionize the vapor of these elements. Resonance transitions of atoms and ions excited by the same laser (by krypton fluoride and xenon fluoride lasers, respectively) are observed for tantalum and uranium. It ishas been suggested that these elements may be used as “catalysts” for “ catalytic” resonance ionization (CATRION) of dense multicomponent gas mixtures. Experiments have been carried out to study the krypton fluoride laser irradiation of expanding vapor clouds of different elemental composition, created by the evaporation of targets with a ruby laser. Photographs obtained with an image converter, measurements of the refractive index gradient from the deflection of the laser beam, as well as probe and spectroscopic measurements indicate that the clouds undergo photoresonant ionization if they contain tantalum vapor but that the laser radiation has no influence otherwise. Pis’ma Zh. Tekh. Fiz. 23, 24–32 (May 12, 1997)     

Room-temperature deposition of carbon nanomaterials by excimer laser ablation

Numerous investigators have reported on pulsed laser deposition of carbon nanotubes, mostly using the Nd:YAG laser for ablation. In all cases the depositions have been conducted at high-temperatures and high pressures. Here we report on the deposition of carbon nanostructures at room temperature using a 248 nm excimer laser nm to ablate mixed graphite-nickel/cobalt targets. We find that the formation of the carbon nanomaterials is dependent on the particular ambient gas employed. In O₂ gas, carbon nanotubes and nano-onions are produced. The nanotubes have notably large channel diameters of 100-200 nm and the nano-onion structures are 100-200 nm in diameter, also much larger than previously observed. High-resolution, in-situ, time-resolved emission spectroscopy has been used to follow the production of molecular carbon species such as C₂ and C₃, as well as metals such as Ni or Co in the different ambients employed. Spectral modeling reveals significant differences in the vibrational-rotational temperatures of C₂ spectra in O₂ versus Ar. Mechanistic details of the formation of carbon nanotubes and nano-onions, and in-situ optical emission spectroscopy are described.     

Nanomechanical properties of silicon surfaces nanostructured by excimer laser

Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm⁻². A single-crystal silicon [311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses.     

Ultraviolet HeCd laser pumped by a high-frequency electron beam

An electron beam with a large cross section and with a repetition rate of 3×10⁵ pulses per second in a packet has been obtained for the first time. With this beam a HeCd high-pressure laser has been developed and high-frequency lasing on the Cd ion at a wavelength of 325 nm has also been achieved for the first time. Pis’ma Zh. Tekh. Fiz. 23, 44–47 (March 26, 1997)     

Picosecond laser heating and melting of graphite

Ultrashort laser pulses impinging onto solid, strongly absorbing surface deposit their energy within an absorption depth from the surface. This localized energy deposition may result in rapid and very efficient heating of the surface to temperatures far exceeding the melting or boiling point. Temperature evolution at the surface of samples and their electronic structure may be studied with nonperturbing, time-resolved optical diagnostic techniques. Picosecond laser pulses provide the fastest means for heating matter at high temperature, since the characteristic energy transfer times from photoexcited electrons to the lattice occur in this time scale. Surface evaporation is not affecting the observations in this time scale, simply because there is no time for the surface atoms to escape. As an illustration, measurements on graphite are presented here. The complex index of refraction of highly oriented pyrolytic graphite (HOPG) during picosecond laser irradiation has been measured at 1.06 m via time-resolved ellipsometry at angles of incidence up to 80. In particular, a value of the complex index of refraction for the liquid phase has been derived.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.     

Study of ultra-shallow pn junctions formed by excimer laser annealing

Excellent ultra-shallow p⁺n junctions have been formed by thermally treating the BF₂⁺-implanted Si samples by excimer laser annealing (ELA) at 300–400 mJ cm⁻² with post low-temperature long-time furnace annealing (FA) at 600 °C. A junction with a leakage current density lower than 20 nA cm⁻² and a sheet resistance smaller than 200 Ω □⁻¹ can be well achieved. No considerable dopant diffusion is observed by using this low-thermal-budget annealing process. However, by simply using the ELA treatment at 300–400 mJ cm⁻², the resultant junction shows a leakage current density as high as 10⁴ nA cm⁻² and a peripheral leakage current density of 10³ nA cm⁻¹. The large junction leakage is primarily due to the leakage current generated within the junction region near the local-oxidation-of-silicon (LOCOS) edge, and which is substantially caused by the ELA treatment. The large peripheral junction leakage current density can be significantly reduced to be about 0.2 nA cm⁻¹ after a post low-temperature FA treatment at 600 °C. As a result, the scheme that employs ELA treatment with post low-temperature FA treatment would be efficient for forming excellent ultra-shallow p⁺n junctions at low thermal budget.     

Enhancement of ceramic-to-metal adhesive bonding by excimer laser surface treatment

A silicon nitride (Si₃N₄) based ceramic cutting material and a structural alloy steel (SAE 4340) were surface-treated using a 800 mJ KrF excimer laser with an aim to improve the ceramic-to-metal bond strength. For these two materials, the effects of laser energy density and the number of pulses upon the surface morphologies of the laser-treated surfaces to be joined were examined. Conical surface microstructures were generally observed on the laser-treated surfaces of the Si₃N₄ material, and the number of conical features was found to be significantly influenced by the laser energy density. Moreover, the results of XPS have shown that the surface chemistry of the ceramic was altered after being laser treated. On the other hand, excimer laser treatment had caused the alloy steel surfaces be melted and resulted in some “beach-mark” features. However, the laser energy density has little effect on the overall surface morphology and the roughness of the treated surfaces. Shear tests were performed on adhesive bonded samples of the laser-treated ceramic and alloy steel. Significant improvement in adhesion shear strength was obtained for the laser-treated samples as compared with those tested in the as-received and mechanically abraded conditions. The required laser operation condition for achieving good shear joint strength was discussed.