Research and development of new laser source and their application 

  • Optimization of the developed at MVL laboratory pulsed visible copper bromide (CuBr) laser, aimed at longer lifetime, increased efficiency, better beam quality and higher output power continued. A patent protected method for increasing the lifetime of a powerful 40-W CuBr laser by a cold point laser tube was demonstrated and studied. The spectral and pulse characteristics at different excitation frequencies were investigated. The developed in the laboratory CuBr laser is produced by a Australian company Norseld Pty Ltd for medical applications and by a Bulgarian company Pulselight Ltd., with which there are permanent contacts for scientific support for manufacturing CuBr laser tubes [P1, P2]. Parametric studies of the interaction between the laser beam from a copper bromide vapour laser and different materials (Cu, Al, Ti) were carried out in order to optimize the     processes of laser drilling, cutting and marking. A master oscillator-power amplifier (MOPA) system, based on the atomic CuBr laser with divergence close to the diffraction limit (100 μrad) and maximum output power of 100 W was developed. The effect of hydrogen on the system performance and the coherent properties of the CuBr amplifier system were investigated. Divergence-evolution studies were carried out to improve the spatial coherence and reduce the laser beam divergence. Manipulating the laser pulse shape of the MOPA system was realized.

 

40-watt-cubr
The 40-W CuBr laser 

 

  • Development and optimization of the invented at MVL copper ion UV laser, oscillating in Ne-CuBr nanosecond pulsed discharge continued. The effect of different admixtures on the laser oscillation parameters was investigated. It was demonstrated that small admixtures of hydrogen (0.2-0.4 Torr) increase of twice in the laser output power. Lifetime investigations under a stabilized temperature regime of the active zone were carried out. An average output power of 500-600 mW, beam divergence of 0.1 mrad and laser tube lifetime of 700 hours were achieved.

 

uv-ne-cubr
The UV Ne- CuBr laser

 

  • Investigations of a strontium recombination laser, oscillating at 6.45 microns in nanosecond He-Sr discharge were performed. A record average output power of 12.5 W was obtained. A new version of the strontium atomic laser oscillating in He-SrBr2 discharge was developed. Laser generation of the following atomic and ion lines: 1.03 mm, 1.09 mm, 2.06 mm, 2.20 mm, 2.69 mm, 2.92 mm, 3.01 mm, 3.07 mm and 6.45 mm was achieved and the optimal conditions were determined. Different tube designs were studied with the aim to increase the output power of the 6.45 mm. 

  • Various hollow cathode geometries were tested at discharge parameters typical for laser generation of ion lines in hollow cathode discharge. The optimal plasma conditions for efficient cathode sputtering and excitation of laser lines in He-Cu discharge were determined.

Applications:

The MOPA copper bromide laser system was applied for precision processing of different types of hard materials such as metals, ceramics and plastics; for drilling microholes, for marking and cutting. It was used for high-precision micromachining of nickel and tool steel samples in order to improve their mechanical characteristics for application in automobile industry in the frame of a project with University of Windsor Canada. The laser micromachining consists in drilling of microholes in highly polished square plates with 10-mm size of the corresponding material. New software is developed to control the MOPA system and the XY table, on which the samples are placed, for drilling of the microholes by special patterning, i. e. in the apex of equilateral triangle and microhole depth is equal to the hole radius. The microhole diameter and the distance between their centres (the side of the equilateral triangles) are varied for each sample. A minimal hole diameter of 4-6 mm and heat affected zone of 0.3 mm are achieved.
The CuBr laser is used for induced laser–liquid–solid formation of extracellular matrix/hydroxyapatite composites and for creating micrometer-scale structures by precise and flexible irradiation of small and complex shapes.
The developed UV Ne-CuBr laser was used for laser-induced modification by 248.6 nm line of a conducting polymer. A significant growth of copper electrocrystallization on the polymer layers was achieved. The refractivity of polymer layers in the visible and ultraviolet spectral range was determined. Fabrication and testing of optical elements, as well as processing of polymer film substrates for Nemoptic Company, France was done. Micron holes of 10, 20 and 40 microns in size were drilled in glass, polymer and ZnSe. Structural modifications in the surface layer of copper and aluminium were investigated by the use of visible laser radiation.
On the base of both high-power mid-infrared He-SrBr2 and deep-ultraviolet Ne-CuBr lasers, two laser systems equipped with opto-mechanical systems to control laser beam have been developed for application to the treatment of PEDOT films with DUV laser output and to determine optical linear properties of CaxSr1-xF2 crystals in the midinfrared, visible and deep-UV spectral regions.
Interdisciplinary research based on application of different laser techniques for diagnostics, restoration and conservation of cultural heritage has started. The investigations are in the frame of a big project of the department and participations of scientists from the National Institute of Archaeology with Museum, BAS and Sofia University, with the financial support of the National Science Fund. An interdisciplinary team of experts in the field of physical archaeometry was formed. New modern laboratories for qualitative and quantitative spectral analysis of different artifacts based on laser induced plasma (LIBS) and fluorescent (LIF) diagnostics were equipped. Analysis of different ceramic, glass and metal artifacts was done. Diagnostics of valuable museum objects (gold and gilded objects, for example) were performed in-situ with the portable LIBSCAN apparatus. In-situ analyses of metallurgic ovens near ancient copper mines in the region of Sozopol were also done. The developed apparatus and methods can be applied for remote element control in real-time during the process of new material synthesis or other technological processes, as well as for diagnostics of environment pollution or wasted industrial zone contaminations.
Laboratory set-up for laser cleaning based on CuBr and Q-switched Nd:YAG lasers was built with optical systems for guiding the laser beam. The cleaning parameters for different stone, marble, metal and leather samples were determined. Preliminary tests of laser cleaning of real marble and metal archaeological artefacts were done. The research is done in collaboration with INOE, Bucharest, under a bilateral project.