Copper Vapor Laser Beam Research Articles

Local Crystallization of Lithium-Niobium-Silicate Glass by Copper-Vapor Laser Beam

The possibility of laser crystallization of lithium-niobium-silicate glass by means of visible- and UV-range nanosecond pulses is demonstrated. Glass with the composition 32 mol.% Li2O, 26 mol.% Nb2O5, and 42 mol.% SiO2 was irradiated with a copper vapor laser in the sum-frequency lasing regime at wavelength 271 nm. Glass additionally containing 1.5 mol.% Nd2O3 was irradiated. Local Raman scattering spectroscopy showed the crystal structure formed to be ferroelectric lithium niobate LiNbO3.

Impacts of Acetone–Butanol–Ethanol (ABE) ratio on spray and combustion characteristics of ABE–diesel blends

Abstract Acetone–Butanol–Ethanol (ABE), the intermediate product while producing bio-butanol, has been proposed to be used as an alternative fuel directly to reduce the butanol recovery/separation costs. It is important to understand how the ABE ratio influences the combustion process because of the large differences in physical and chemical properties between the ABE components and diesel. Therefore, a wide range of ratios of ABE (0%, 20%, 50%, and 80% in volume referred to as D100, ABE20, ABE50 and ABE80 respectively) were blended with diesel and combusted in a constant volume chamber under various ambient temperatures (1200 K, 1000 K, and 800 K) and various ambient oxygen concentrations (21%, 16%, and 11%). Mie scattering images of the liquid spray and broadband flame luminosity images were captured by a high speed camera coupled with a copper vapor laser beam as light source. The results show that ABE20 exhibits spray characteristics similar to those of D100 while ABE50 exhibits spray characteristics similar to those of ABE80. However, the sprays of ABE50 and ABE80 are much shorter and narrower compared to those of D100 and ABE20. It is predicted that there exists a critical ratio between 20% and 50% for ABE, beyond which the spray characteristics of the blend will be dominated by ABE. The intermediate ABE blend, ABE50 achieves a shorter ignition delay (slightly longer than that of D100) and combustion duration compared to those of ABE20 and ABE80 because of its improved spray performance and relatively low latent heat and high cetane number. The natural flame luminosity is found to be reduced significantly with an increasing ABE ratio due to the fuel-borne oxygen that accelerates soot oxidation along with longer flame lift-off length that effectively decreases the equivalence ratio in the combustion region. Overall, ABE50 is the blend that displays combustion characteristics similar to neat diesel while achieving a shorter combustion duration and lower natural flame luminosity. Thus, ABE50 could potentially increase thermal efficiency and decrease soot emissions when applied in diesel engines.

Spray and Combustion Characteristics of Neat Acetone-Butanol-Ethanol, n-Butanol, and Diesel in a Constant Volume Chamber

Intermediate product of biobutanol production, acetone-butanol-ethanol (ABE) as an alternative fuel has drawn increasing attention in recent years due to its potential to eliminate various production costs. In this work, neat acetone-butanol-ethanol (ABE) with a component volumetric ratio of 3:6:1, n-butanol, and neat diesel were studied in a preburn type constant volume chamber with optical access. The ambient temperature and oxygen ranged from 800 to 1200 K and 21% to 11%, respectively, covering both conventional and low temperature combustion (LTC) regimes. Time resolved images of the spray and natural flame luminosity (indicator of soot) were captured by a high speed camera coupled with a copper vapor laser beam. The images show that the flame lift-off length and liquid penetration of n-butanol and ABE are much longer and shorter, respectively, than that of diesel under all tested conditions. This results in a longer “gap” between the liquid spray and the flame in ABE and n-butanol combustion that provides more space and time for the droplets to evaporate and mix with the ambient air, which is expected to decrease the local equivalence ratio at the combustion region. Indeed, the natural flame luminosity of ABE and n-butanol is reduced significantly under all tested conditions compared to that of diesel. For all the tested fuels, especially ABE, the combustion duration decreases with the reduction of ambient temperature due to a stronger premixed combustion, while it increases with the reduction of oxygen concentration due to the dilution effect. Therefore, ABE has a high potential to reduce soot emissions when used in diesel engines, but it would also suffer from combustion phasing retardation like butanol under LTC conditions with high EGR.

Comparative study on second harmonic conversion and saturation characteristics of three copper vapor laser beams of same average power and different spatial coherence

This paper presents a comparative study on second harmonic conversion and saturation behavior of three copper vapor laser (CVL) beams of same average power up to 11 W (510 nm), however with different spatial coherence width of 17%, 35%, and 100% of the full beam cross-section. The nonlinear crystal employed is beta barium borate. It is observed that the trends in second harmonic (SH) conversion efficiency and its saturation are widely different for the three CVL pump beams. As expected, the conversion efficiency scaled up with increase in pump power. However, very interesting trends are observed in SH saturation characteristics with scaling of pump beams spatial coherence. For lower coherence CVL beam, the saturation of SH efficiency is observed at lower pump flux and at higher average power. Also, the saturation occurred at lower SH efficiency for CVL beam of lower spatial coherence. The fall in the SH efficiency after the peak is more rapid for lower spatial coherence pump beam. The experimental trends are explained in terms of combined effect degree of spatial coherence of pump beams and the thermal dephasing in the nonlinear crystal by high pump average power.

Role of optical resonator on the pointing stability of copper vapor laser beam

This paper presents a first comprehensive study on the pointing stability of copper vapor laser with an emphasis on bringing out the role of optical resonator. Long term (∼10min), single pulse, far-field beam pointing stability of a 5.5kHz repetition rate copper vapor laser (λ=510nm) with plane–plane, unstable and filtering resonators, is studied. It is established that the resonator optics largely decides the CVL pointing stability. Minimum beam pointing angle of 8μrad from generalized diffraction filtered resonator (GDFR) is obtained in contrast to a maximum value of 120μrad from the plane–plane resonator. The unstable resonators data is in between. The relative trends in CVL pointing stability are discussed in terms of wave-front distortions due to resonator mode build up from optical noise, thermal and mirror misalignment effects. The degree of optical resonator immunity to phase distortions dictates the net pointing stability achieved.

Thermal dephasing in second-harmonic generation of an amplified copper-vapor laser beam in beta barium borate

The conversion efficiency in second-harmonic generation of an amplified beam in a master-oscillator power amplifier copper-vapor laser (CVL) is lower than that of the oscillator beam alone. This lower efficiency is often vaguely attributed to wave-front degradation in the amplifier. We investigate the role of wave-front degradation and thermal dephasing in the second-harmonic generation of a CVL from a beta-barium borate crystal. Choosing two beams with constant intrapulse divergence, one from a generalized diffraction filtered resonator master oscillator alone and other obtained by amplifying oscillator by use of a power amplifier, we show that at low flux levels the decrease in efficiency is due to wave-front degradation. At a fundamental power above the critical power for thermal dephasing, the decrease is due to increased UV absorption and consequent thermal dephasing. Thermal dephasing is higher for the beam with the lower coherence width.

Nonlinear frequency conversion of copper vapor laser radiation using convergent and parallel laser beams

Results of experiments are presented on the comparison of the efficiency of radiation generation at the sum frequency (λ=0.271 µm) of copper vapor laser (CVL) in a nonlinear DKDP crystal using either convergent or parallel laser beam. An intensity of UV radiation of 0.34 W and a conversion efficiency of 6% obtained under conditions of strong focusing occur to be substantially lower as compared to those obtained using a parallel laser beam of the same power (0.73 W and 12%, respectively). Experimental data on the structure of a CVL beam generated with an unstable resonator are presented, and physical reasons for the limitation of the efficiency of nonlinear frequency conversion are analyzed.

Spatial coherence of the generalized diffraction-filtered resonator copper vapor laser

The results of a study on the spatial coherence of a generalized diffraction-filtered resonator (GDFR) copper vapor laser (CVL) for various magnifications are presented. The coherence width and output power are compared with that of unstable resonators (UR's) of equivalent magnifications. It is established, by use of reversal shear interferometry, that the GDFR CVL beam has better spatial coherence and average power characteristics than the UR CVL beam for equivalent resonator magnifications.

47-W, 255-nm source based on second-harmonic generation of a copper-vapor laser in cesium lithium borate

We have generated 4.7 W of UV (255-nm) radiation with wall plug efficiency of 0.12% by frequency doubling the green (511-nm) output of a kinetically enhanced medium-scale copper-vapor laser (CVL) in cesium lithium borate (CLBO). Frequency doubling in beta -barium borate produced 3.9 W of UV radiation with wall plug efficiency of 0.1%. We found that conversion was better with CLBO because of the reduced constraints on CVL beam quality, less UV absorption, and smaller UV walk-off.

Intra-pulse decrease of M2 of a copper vapor laser beam

The temporal behavior of the beam divergence of a copper vapor laser (CVL) equipped with on- or off-axis unstable resonators at 510.6 nm has been investigated experimentally and theoretically. The temporal change of the beam divergence is measured using a streak camera and is evaluated by the M 2 factor. Narrowing of the beam divergence during the pulse is observed. Also is found that the difference of the narrowing ratio between the on-axis and off-axis unstable resonators resulted from the near-field pattern of the laser beam.

Spatially confined laser-induced damage of Si under a liquid layer

Experimental results are presented on the Si damage induced by a copper-vapor laser beam under a layer of chemically neutral liquid (H2O, DMFA, DMSO). The lateral dimensions of the damaged area coincide with those of laser beam, while the depth of the damaged area increases with time. The rate of hole formation may be as high as 75 μm/s. The qualitative interpretation of the results is given on the basis of laser generation of vacancies, and their combination and redistribution in the field of the inhomogeneous mechanical strains due to multiple heating/cooling cycles of the surface of the semiconductor.

Time-resolved measurement of spatial coherence of a copper vapor laser beam using a reversal shear interferometer

We have measured the temporal change of spatial coherence of a copper vapor laser (CVL) beam with an unstable resonator by a reversal shear interferometer and a streak camera. By this method, we can evaluate the temporal change of the spatial coherence function from a single-shot measurement. We have observed stepwise increase of the coherence width at intervals equal to the transit time of the resonator. The values of the first, second and third plateaus were 5 mm, 6.7 mm and 13 mm, respectively, when an unstable resonator of magnification factor 60 was used. Moreover we have verified the result by a theoretical calculation on the basis of a passive resonator model.

One watt average power by second harmonic and sum frequency generation from a single medium scale copper vapor laser

Ultraviolet (UV) powers of over 1 W have been obtained by second harmonic and sum frequency generation from a single medium scale (20 W) copper vapor laser (CVL) using a new focal geometry in which the CVL beam is focused in only one direction to produce a line focus within a BBO crystal. High optical conversion efficiencies, 20 and 30%, are observed for the low divergence ( approximately -10 times the diffraction limit) and diffraction-limited components of the CVL output, respectively. Wall-plug efficiencies for UV generation are up to 0.04%. Efficient frequency conversion has also been demonstrated for CVL operating conditions unsuited to the generation of diffraction limited output. >

Laser-assisted engraving of HgCdTe under a liquid layer

Experimental results are presented on spatially confined damage of Hg x Cd 1- x Te induced by a copper-vapor laser beam under a layer of either a Br-containing liquid or a chemically neutral liquid (H 2O, DMFA, DMSO). Engraved grooves have a triangular profile with a minimal width of 5 μm. The thickness of the nonstoichiometric layer of s/c is about a few μm. Via-holes produced in the s/c under a layer of liquid containing organometallic molecules (soluble compounds of Au, W, Mo) provide the interconnection of two sides of a s/c wafer with a DC resistance of 5 Ω at 77 K.

Kinetics of laser-induced Au pyrolytic deposition from the liquid phase

Kinetics of Au pyrolytic deposition from organic solutions of triphenyl phosphine complexes induced by a copper-vapor laser beam is studied experimentally. Activation energies Ta and pre-exponential factors are determined for 7 different Au complexes. Measured Ta values range from 1800 K to 9400 K. The average temperature of the GaAs wafer is found to be 70° C for a laser beam power of 10 mW.

Non-collinear interaction model of the second harmonic generation of a copper vapor laser

We estimated theoretically the conversion efficiency of the second harmonic generation of a copper vapor laser (CVL) beam. Since the CVL beam is only partially coherent, the theory for the coherent beam is useless for the second harmonic generation of the CVL beam. The focused CVL beam was considered as a set of bundles of rays with propagated in different directions through a crystal and non-collinear interaction between these bundles of rays was investigated. On the basis of this model, we found that the conversion efficiency depends on the product of the beam divergence and the beam diameter, and the length of a nonlinear crystal.

Beam quality improvement of a copper vapor laser by long pulse excitation and injection locking.

Laser oscillations with nearly diffraction limited output beam of a copper vapor laser (CVL) were investigated. The beam divergence less than 0.3 mrad in the pulse duration of 75ns was attained by the long pulse excitation. Also, good beam quality in the whole pulse duration was obtained by the injection locking, with the threshold injection power of only 0.1 W. The CVL beam quality has been successfully established for the master oscillator power amplifier.

Thermally induced refractive index gradients in a dye-laser cell

The program GABI calculates refractive index gradients generated in a dye solution, flowing in a planar cell, and pumped by a repetitively pulsed copper vapor laser beam. The calculation results serve for design evaluation and selection of optimal pump geometry, dye solvent and dye solution flow velocity.