Elena A. Shakhno

Laser–induced film deposition by LIFT: Physical mechanisms and applications

Peculiarities of the technique of the laser-induced film transfer (LIFT) are investigated. Possible mechanisms of tearing-off and transference of the films from the donor substrate (target) to the acceptor one are investigated. The main fields of LIFT applications are considered. One of the most interesting directions of LIFT applications—decontamination of radioactive surfaces—is investigated in detail. The main peculiarities and regimes of the processing are defined.

Pulsed laser ablation mechanisms of thin metal films

The ablation of thin films by single laser pulse is a well known technique with widespread industrial applications. Ablation occurs in a well defined power density region if a supported thin film is illuminated by a single laser pulse. In the literature there are a number of theoretical description of ablation, but a very few based on in-situ experiments. In our study we have directly visualized the ablation processes with fast photography based on application of dye laser probe pulses. The ablation of chromium and tungsten layers supported onto glass substrates with pulses of ArF excimer laser was investigated. The ablated area was illuminated by a delayed short pulse of a fluorescein dye laser or a Rhodamine6G dye laser. Snapshots of initial phase of ablation and the forthcoming material transport were recorded by an optical system and a video camera. Blowing-off mechanisms and thermo-mechanical mechanisms are considered to take place during ablation. Pressures formed during laser ablation were calculated and compared with experimental data. It was found that thermo- desorption of gas adsorbed on to the substrate surface, substrate materials evaporation and film exfoliation by its longitudinal thermal enlargement may be acting during laser ablation of thin films.

Local laser-induced deposition of thin films

Possible mechanisms of tearing off and transference of the film from the donor substrate (target) to the acceptor substrate as a result of a local laser action are considered. Thermal, gas-dynamic and hydrodynamic models for explanation of a number of effects observed at local laser film deposition are proposed. The range of technological parameters close to optimal ones is determined.

Laser Cleaning of Metal Surfaces: Physical Processes and Applications

Physical processes occurring by laser cleaning of metal surfaces from soiling particles, coatings and near-surface oxide or corroded layer are considered. Unconventional methods of laser cleaning which promote increasing the quality and effectiveness of cleaning and solving of the problem of soiling substance gathering are proposed. Applications of these methods in a number of novel fields, such as pinholes cleaning, coatings removal, radioactive contaminated layers removal, cleaning of objects of historic and cultural heritage are considered.

Laser decontamination of radioactive nuclides polluted surfaces

The article is devoted to the results of the regular researches in laser decontamination. Task relevance is discussed. Basic theoretical principles of laser cleaning are considered. Decontamination factor measurement method is described. Experimental results for different materials and laser sources are presented.

Mechanisms of local laser-induced front transfer of films

Peculiarities of the technique of the local laser-induced front transfer (LIFT) of thin films are investigated. Possible mechanisms of tearing-off and transference of the films from the donor substrate (target) to the acceptor one are considered. Thermal, gas-dynamical and hydrodynamical models are proposed for explanation and numerical estimation of a number of effects observed with local laser film deposition. Applications of the LIFT method are considered.

Thermomechanical mechanisms of laser cleaning

The physical mechanisms of dry and steam laser cleaning of the surface are investigated theoretically. At dry laser cleaning particles are removed from the surface due to inertial force that caused by particles and/or substrate thermal expansion by light absorption and thermal conduction. The condition of complete particle removal, when it does not return to the substrate, is defined. The considered physical mechanism of dry laser cleaning is propagated to multipulse regime. The physical mechanisms of steam laser cleaning are proposed to be caused by liquid layer vaporization near the particle surface due to substrate and/or particle light absorption and non-uniform action of vapor pressure to the particles. The evaluated thresholds of dry and steam laser cleaning are in a good agreement with known experimental data.

Local laser-induced film transfer: theory and applications

The technique of the local laser-induced film transfer (LIFT) is considered. The peculiarities of the front LIFT and the back one are investigated. The main fields of the LIFT applications are considered. Some particulars of the front and back LIFT applications--laser trimming of the coordinate characteristic of the position sensitive photoreceiver and deposition of the quartz glass local cover on to the silicic substrate--are considered in detail.

Laser technologies in micro-optics. Part 1. Fabrication of diffractive optical elements and photomasks with amplitude transmission

This paper is a review of studies carried out by the staff of the National Research University of Information Technologies, Mechanics and Optics (ITMO University, Saint-Petersburg) and the Institute of Automation and Electrometry of the Siberian Branch of the Russian Academy of Sciences (IAE SB RAS, Novosibirsk) in the field of development of laser engineering processes for the formation of the structure of diffractive optical elements (DOEs) and photomasks with amplitude binary and grayscale transmission. This paper also describes the results of the study of laser thermochemical technology for fabricating chrome DOEs and technologies for the fabrication of grayscale DOEs and photomasks based on the use of amorphous silicon and LDW glass.

Laser polishing of vidicon's glass substrates

Many micro- and nanoelectronic, micro- and nanooptic devices include different films and layers deposited at the surfaces of dielectric substrates. Properties of these films and layers sufficiently depend on properties of the substrate surface. Therefore substrate surface preparation before layers and films deposition is very important. One of the main parameters of the surface is its roughness that influence on such parameters of thin layers as specific resistance, electric strength, chemical resistance etc. By mechanical treatment of the surface its roughness is defined by the size of polishing powder grain. That is why preparation of the surface with low roughness is laborious one. Besides, preliminary mechanical grinding with coarse-grained powder causes appearance of near-by-surface cracked layer, which can be removed by deep mechanical, chemical or flame polishing. Laser polishing is sort of last one. The problem of laser polishing was repeatedly discussed. 10.6 μm CO2-laser is the only acceptable one, as all glasses well absorb radiation at this wave length. The regime of continuous radiation is used in most cases, for which typical duration of influence by surface scanning is several milliseconds. Though the beneficial effect was obtained (in before mentioned and other papers), the technique is not wide spread. In our opinion the reason of this is that there are problems connected with phenomena specific for laser polishing: hydrodynamical waves in the softening layer and thermomechanical tensions in the substrate. Both of them are aggravated by the three-dimensional locality of laser action. This situation can be changed by using of short nanosecond laser pulses - in this case the heated layer of substrate decreases and the problem becomes not so critical.