Cw Argon Laser Research Articles

Photoacoustic characterization of cw argon-ion laser irradiation of Ge

Photoacoustic detection has been used to characterize cw argon-ion laser irradiation of Ge. Laser-induced heating, damage, and melting are studied. The heating process is seen to be nonlinear with incident laser power until close to melting. Two laser-induced-damage time constants are obtained associated with thermal etching and oxidation. An incident power level of 2.24 W is estimated to initiate the melting of an undamaged Ge surface under the experimental conditions described.

Lanthanide ion probes of structure in biology: Environmentally sensitive fine structure in laser-induced terbium(III) luminescence

The 488 nm line of the CW argon ion laser provides a convenient visible source for the direct excitation of the emissive 5D 4 state of the Tb(III) ion. Room temperature emission spectra of Tb(III) in a variety of environments have been examined under relatively high resolution. The samples studied include structurally well-characterized crystalline solids, model chelate complexes in solution and Tb(III) bound to the enzyme thermolysin and the protein parvalbumin. The fine structure in the emissions is caused by ligand field splittings of both ground and excited state J manifolds. These spectra provide signatures sensitive to the immediate coordination environment of the Tb(III) ion. Solid state/solution state structural comparisons are made. The emission fine structure reveal differences between the EF side calcium-binding sites of parvalbumin and the calcium site 1 of thermolysin.

Cw argon laser annealing of ion-implanted silicon

We report on the annealing behavior of ion-implanted silicon exposed to cw argon laser radiation. The quality of the annealing was studied using channeling, in situ reflectivity, phase-contrast microscopy, and electrical resistivity. Strong dependence of anneal quality on laser power, crystal orientation, and implant dose is reported. Reflectivity measurements with a focused probing laser show that the onset of annealing occurs just below the melting point, and the annealing extends into the region where a thin layer of liquid silicon is formed at the crystal surface. We conclude that the physical mechanism responsible for crystal recovery is similar to the solid-state epitaxial regrowth observed for over-annealed samples.

On the effects of different laser energy sources upon the iris of the pigmented and the albino rabbit.

The irides of pigmented and albino rabbits have been irradiated by a) a CW argon laser beam (exposure duration up to 1 s), b) a 1 ms pulses Nd:YAG laser and c) a 30 ns pulses Q-switched ruby laser. The immediate and long-term pathologies were analysed by scanning and transmission electron microscopy over a period of 13 months. At both the gross and ultrastructural levels, damage configuration may differ considerably, depending on the three modes of irradiation. For each source there are both thermal and mechanical damage components and the significance of mechanical effects increases with decreasing pulse duration for a constant pulse energy. In the argon experiments, tissue destruction is predominantly a consequence of heat, resulting from conduction and convection. The subsequent regeneration of tissue after such heat-induced trauma is fast. The effects of the Nd:YAG laser, at the irradiance levels used in the present study, are again predominantly of a thermal nature and are caused by heating and local evaporation. The pigmented and the nonpigmented iris epithelium are destroyed and widespread decay of the stroma occurs over some months. Such damage never results in full repair. The most prominent feature of Q-switched ruby laser irradiations is their independence of the iris pigment content. In contrast, at the energy levels studied, the argon laser is entirely ineffective, whilst the effect of the Nd:YAG laser is much reduced in the absence of pigment. The consequences of these findings for the clinical applications of such lasers are discussed.

Continuous-wave backward-wave generation by degenerate four-wave mixing in ruby

This is the first reported demonstration of cw wavefront conjugation by degenerate four-wave mixing in a solid. Conversion efficiencies of 3% for conjugate-wave generation were obtained in a ruby crystal using a cw argon-ion laser.

Mode selection in high-power argon lasers

An analysis is made of the feasibility of using various types of resonators for mode selection in a highpower cw argon laser with large-aperture discharge tube. Three resonator configurations were investigated experimentally. Single-frequency radiation with a power of 20 W at λ =514.5 nm and a coefficient of conversion to the single-frequency regime of η≈0.4 was obtained from an argon laser with a discharge tube of diameter d =14 mm and active length l0≈1.7 m. Some aspects of further improvement of the output parameters of a high-power argon laser with mode selection are discussed.

Isotope fractionation in two-step photoionization of Li 2

A cw argon-ion laser beam intersects a thermal-energy lithium-beam. Sequential two-photon ionization of Li 2 is observed. Li + 2 ions are formed by most of the available laser lines. Large isotope fractionations result from this process.

Picosecond excitation of I 2 B→X Emission in CCl 4 solution: ultrafast decay and spectrum

Excitation of the B 3π 0 + u state of I 2 in CCi 4 solution with ≈8 ps fwhm 531 nm mode-locked pulses yields substantial fluorescence, which contrasts with the pure resonance Raman emission spectrum displayed under 514.5 nm cw argon ion laser pumping.

Photodissociation of positive cluster ions by CW and pulsed laser radiation

Several positive cluster ions, formed at temperatures around 130 K in a supersonic flow apparatus, have been examined for their photosensitivity. Two laser light sources were used: a modulated CW argon ion laser, emitting several lines in the blue—green spectral region, and a pulsed nitrogen laser emitting at λ = 337.1 nm. Fragmentation cross-sections (σ f) are calculated relative to those for the species O 2 +(H 2O) in the visible and for N 2 +(N 2) in the ultraviolet. Rough estimates for the absolute values give σ f for the former ion as 1.1 × 10 −18 cm 2 at λ = 514.5 nm and 5 × 10 −18 cm 2 for the latter ion at λ = 337.1 nm. The ions with the largest σ f are NO +(NO) and NO +(NO)(NO 2); for these ions σ f exceeds 10 −17 cm 2. Most of the cluster ions studied seem to photodissociate via a transition to a purely repulsive state. The hydrate ions O 2 +(H 2O) 1,2 show unusual behaviour in that the first, but not the second, hydrate is photosensitive. The effect of imposed electric fields on the apparent values of σ f is discussed, with particular reference to the ions H +(H 2O) n . The implications of the results for ionospheric chemistry are considered.

Laser photoluminescence of zirconium oxide at 4 K

Laser induced photoluminsecence spectra of ZrO trapped in Ne at 4 K have been obtained. Continuous wave tunable dye and cw argon ion lasers were used to excite ZrO from the X 1Σ+ ground state to the e 1Π and B 3Π electronic states, respectively. Red emission from e 1Π (v=0) →X 1Σ+(v=0,1,2) was observed. In addition, e 1Π (v=0) and e 1Π (v=2) have been found to undergo matrix induced intersystem relaxation into the E 3Π and A 3Φ states, respectively. Infrared emissions of ZrO have been observed and tentatively identified as belonging to E 3Π→X′ 3Δ and e 1Π→c 1Δ. Bandheads of observed transitions are shifted not more than 2% from known gas-phase values. Line shapes of the transitions to the ground state from the e and B states are characterized by a sharp zero-phonon line accompanied by a multiphonon sideband. An additional system overlapping the e 1Π−X 1Σ+ system has been observed and is identified as the A 3Φ2→X′ 3Δ1 band system. The energy of the low-lying c1Δ and X′ 3Δ states are determined to be 5200 and 1650 cm−1 above the ground state.

Evaluation of C 2 resonance fluorescence as a technique for transient flame studies

Resonance fluorescence from C 2 in flames induced by the 514.53 nm line of a cw argon ion laser has been studied experimentally and theoretically using computer-generated spectra. An assessment is made of the feasibility of resonance fluorescence techniques for making real-time measurements of C 2 number density fluctuations in atmospheric hydrocarbon flames.

Automatic ultrasonic absorption spectrometer

A completely automatic ultrasonic absorption spectrometer covering the frequency range from 5 MHz to in excess of 250 MHz has been developed. The instrument utilizes Debye–Sears and Bragg reflection of light to modulate the output of a cw argon-ion laser and is interfaced to a minicomputer that interactively controls experimental parameters and accumulates data.

Anomalies in scattered spectra of a hydrogen arc plasma irradiated by a continuous argon ion laser

Results of scattering diagnostics oń a magnetically stabilized arc with a CW argon ion laser are presented. For certain parameters of the experiment the scattered spectrum deviates considerably from the expected profile.

Laser destruction of photosensitized superficial malignant tumours

After intraperitoneal administration the photosensitizing dye acridine orange localized to malignant mouse tumours. Subsequent irradiation with a cw argon laser, at energy levels that did not cause heat damage, produced destruction of these tumours. In nine out of ten mice there was no evidence of regrowth after four months.

CW Thomson scattering from a low electron density hydrogen plasma using a photon counting technique

Thomson scattering from a low electron density (3×10 12cm −3) stationary hydrogen plasma was performed using a 3 watt CW argon ion laser along with a photon counting technique. An estimation is given for the laser power required for CW Thomson scattering in pulsed plasma experiments.

Anomalous competition of λ=488 and 514.5 nm lines emitted by a cw argon laser

An experimental investigation was made of the frequency spectrum of the stimulated emission from an argon laser at ?=514.5 nm in the region of of anomalous competition with a line at ?=488 nm. The relationship between the frequency spectrum and the nature of the optical competition was determined. A mechanism explaining the anomalous interaction between these lines was put forward.

Excitation of optical harmonics in lithium iodate and formate crystals by cw dye laser radiation

The results are given of an investigation of the efficiency of second harmonic generation in lithium iodate and formate crystals (these harmonics are needed in ultraviolet spectroscopy). Ultraviolet radiation of wavelengths shorter than 350 nm was generated for the first time in lithium iodate. The source of exciting radiation was an organic dye laser pumped by a cw argon laser.

Laser photoluminescence of TiO in Ne at 4 °K

Pseudo-gas-phase photoluminescence spectra of TiO isolated in Ne matrices at 4 °K have been obtained. Photoluminescence is induced by laser excitation from the X 3Δ ground state to B 3Π and C 3Δ electronic levels using a cw tunable dye laser and a cw argon ion laser, respectively. Red emission from B 3Π vibrational levels terminating in ground state levels is observed. In addition, the B 3Π (v=0) and B 3Π (v=1) levels have been found to undergo matrix-induced intersystem relaxation into the b 1Π state. Near-infrared emission between excited states in the singlet manifold of TiO has been observed and identified as belonging to the δ (b 1Π→a 1Δ) and the φ (b 1Π→d 1Σ+) band systems. Observed δ and φ emission bands are uniformly shifted by −93 cm−1 and +73 cm−1, respectively, from observed or predicted gas phase bandheads. The line shape of the δ and φ emission in the solid is that of a sharp zero-phonon line accompanied by a broad multiphonon sideband. An additional sharp zero-phonon emission system, here labeled the ζ system, is found to overlap several broad multiphonon bands of the red γ′ (B 3Π→X 3Δ) emission. Evidence obtained supports the tentative conclusion that the ζ system is due to intercombination b 1Π→X 3Δ emission. From the assigned intercombination transition the energy of the low-lying a 1Δ state is determined to be 3500 cm−1 above the X 3Δ ground state. The 3500 cm−1 value for the relative energy between the isoconfigurational a 1Δ and X 3Δ states is in qualitative agreement with theoretical expectations based on consideration of the bonding in the TiO molecule.

Dependence of two-photon absorption efficiency on the relative intensities of two modes simultaneously generated by a cw laser

The two-photon absorption induced by a cw argon laser has been investigated. The efficiency of this process has experimentally been found to depend on the relative intensities of two modes simulataneously generated by the laser. Good agreement with presented theoretical predictions has been established.

Use of argon laser radiation in restoration of single-crystal state of ion-implantation-amorphized silicon surface

High-power (up to 500 W) radiation of a cw argon laser was used to restore the single-crystal state of a silicon surface made amorphous by ion implantation. The experiments were carried out in air and the power density of the laser radiation was 100 W/cm2. The duration of illumination did not exceed several seconds. The experiments were carried out on single-crystal silicon plates doped by implantation of arsenic ions at room temperature (ion energy 100 keV, dose 1800 μC/cm2). Surface melting was observed after several seconds under soft laser heating conditions. Reflection electron micrographs indicated that laser radiation restored the single-crystal structure of an ion-implanted amorphous layer of silicon even when the illumination was brief (3 sec). Complete recovery was achieved after melting the surface.