Emission spectra of MgI and MgII from a plasma induced by the interaction of a laserpulse with the surface of aqueous solutions of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>MgCl</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>, were recorded by a timeresolved spectroscopy method to obtain information on the processes involved in theformation and the evolution of the two different species. A kinetic model based onion-electron recombination produced during the relaxation of the plasma isconstructed with the aim to explain the origin and the temporal shift of observed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mtext>Mg</mml:mtext></mml:mrow><mml:mtext>+</mml:mtext></mml:msup></mml:mrow></mml:math> and Mg emissions. Comparison with the experimental results is presented and discussed.

J.  Ben Ahmed

Z.  Ben Lakhdar

G.  Taieb

Kinetics of Laser Induced Plasma on an Aqueous Surface

The temporal evolution of a plasma formed by the interaction of a Nd-YAG 10 ns laserpulse with the surface of aqueous solutions of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>CaCl</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>, has been observed by analyzing thevariation of the emission spectra of ions and neutral atoms in the time interval after thelaser pulse, 500 ns &#60; t &#60; 5000 ns. The intensity measurements of the lines of CaII at3158 &#197;, 3179 &#197;, 3706 &#197;, 3736 &#197;, 3933 &#197;, 3968 &#197; were used to obtain the electronictemperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math> using a Saha-Boltzmann analysis. The broadening of the resonance lineof CaI at 4227 &#197; was used to deduce the electronic density <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>N</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math>, with the aid of the semiclassicaltheory of Stark broadening. A value of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math> &#8776; 28000 K decreasing slightly to21000 K, and an exponential decay for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>N</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math> were found, with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>N</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math> &#8776; 1:25 &#x00D7; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>18</mml:mn></mml:mrow></mml:msup><mml:mtext>&#x2009;</mml:mtext><mml:msup><mml:mtext>cm</mml:mtext><mml:mrow><mml:mtext>-3</mml:mtext></mml:mrow></mml:msup></mml:math> at 500 ns and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>&#x03C4;</mml:mi><mml:mi>e</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mn>1200</mml:mn><mml:mo>&#x00B1;</mml:mo><mml:mn>50</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math> ns.

N.  Terzi

Temporal Characterization of a Plasma Produced by Interaction of Laser Pulses with Water Solutions

In this paper we report the use of the dual beam thermal lens technique as a quantitativemethod to determine absolute fluorescence quantum efficiency and concentrationquenching of fluorescence emission from rhodamine 6G doped Poly(methylmethacrylate) (PMMA), prepared with different concentrations of the dye. Acomparison of the present data with that reported in the literature indicates that theobserved variation of fluorescence quantum yield with respect to the dyeconcentration follows a similar profile as in the earlier reported observations onrhodamine 6G in solution. The photodegradation of the dye molecules under cw laserexcitation is also studied using the present method.

Achamma  Kurian

Nibu A. George

Binoy  Paul

V. P. N. Nampoori

C. P. G. Vallabhan

Studies on Fluorescence Efficiency and Photodegradation of Rhodamine 6G Doped PMMA Using a Dual Beam Thermal Lens Technique

Changes in the pharmaceutical L-adrenaline-D-hydrogentartrate, incorporated in KBrmatrices, induced by a pulsed carbon-dioxide Transversely Excited Atmospheric(TEA) laser, were observed. Modifications of the sample were monitored via infraredspectra. Special attention was devoted to the dependence of the sample changes on thelaser energy density used. The irradiation of the pharmaceutical has been performedwith two laser lines at wavelengths of about 10.6 &#181;m. The laser lines coincide wellwith the absorption band of the pharmaceutical, which is assigned to the ringvibrations/out-of-plane OH deformation vibrations, within the carboxyl (COOH)group of L-adrenaline-D-hydrogentartrate. Laser energy densities of 1.20 and1.70 J/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>cm</mml:mtext><mml:mtext>2</mml:mtext></mml:msup></mml:math> modified the pharmaceutical/compound. It was found that thismodification is in essence a thermal effect. The level of change showed a dependenceon the laser energy density, number of accumulated laser pulses and temporal shapeof the pulse.

Tatijana S. Jovanovic

Milica R. Bogavac

Bojan B. Radak

Milan S. Trtica

IR Laser-Induced Changes to L-adrenaline-D-hydrogentartrate Incorporated in KBr Matrices

A sensitive method based on the principle of photothermal phenomena to realize opticallogic gates is presented. A dual beam thermal lens method using low power cw lasers in adye-doped polymer can be very effectively used as an alternate technique to perform thelogical function such as NAND, AND and OR.

K. P. Unnikrishnan

Thomas Lee S.

Realization of Optical Logic Gates Using the Thermal Lens Effect

Laser ablation of deposited silver colloids, active in SERS, is carried out at three different laserwavelengths (KrF, XeCl and Nd:YAG at &#955; = 248, 308 and 532 nm respectively). Emissionform excited neutral Ag and Na atoms, present in the ablation plume, is detected withspectral and temporal resolution. The expansion velocity of Ag in the plume is estimated in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>~</mml:mo><mml:mn>1</mml:mn><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mn>4</mml:mn></mml:msup><mml:mtext>m</mml:mtext><mml:mtext>&#x2009;</mml:mtext><mml:msup><mml:mtext>s</mml:mtext><mml:mrow><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>. Low-fluence laser ablation of the colloids yields ionized species that areanalyzed by time-of-flight mass spectroscopy. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>Na</mml:mtext><mml:mo>+</mml:mo></mml:msup></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>A</mml:mtext><mml:msubsup><mml:mi>g</mml:mi><mml:mi>n</mml:mi><mml:mo>+</mml:mo></mml:msubsup><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mtext>n</mml:mtext><mml:mo>&#x2264;</mml:mo><mml:mn>3</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math> are observed. Composition of the mass spectra and widths of the mass peaks are found to be dependenton laser wavelength, suggesting that the dominant ablation mechanisms are different at the different wavelenghts.

R. Torres La Porte

D. Silva Moreno

M. Castillejo Striano

M. Marti&#237;n Mun&#241;oz

J. V. Garc&#237;a-Ramos

S. S&#225;nchez Cort&#233;s

E.  Koudoumas

Laser Ablation Studies of Deposited Silver Colloids Active in SERS

Chemical modifications are expected to be the major type of side-effect in the UV laserprocessing of molecular substrates. For their systematic characterization, studies onpolymeric systems consisting of poly(methyl methacrylate) and polystyrene films dopedwith aromatic dopants exemplifying different degrees of photoreactivity are undertaken. Inparticular, the dependence of the nature and extent of the modifications on chromophoreproperties and laser parameters (laser fluence, wavelength, and number of pulses) isexamined. The substrate absorptivity and the number of employed laser pulses turn out tobe the critical parameters in determining the quantity and nature of photoproducts thatremain in the substrate. The implications of these results for the optimisation of laserprocessing of molecular/organic solids are discussed. It is suggested that the importance ofemploying relatively strongly absorbed wavelengths in laser processing may relate, besidesthe efficient etching and good surface morphology, to the minimization of the chemicalmodifications. In contrast, irradiation with successive laser pulses is indicated to be highlydisadvantageous for the chemical integrity of the substrate. In all, the study of such modelsystems appears to be most appropriate for establishing criteria for the systematicoptimisation of laser processing techniques of molecular substrates.

E.   Andreou

A.  Athanassiou

D.  Fragouli

D.  Anglos

S.  Georgiou

Laser and Material Parameter Dependence of the Chemical Modifications in the UV Laser Processing of Model Polymeric Solids

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Laser Chemistry