The Copper Bromide Metal Vapor Laser
Annotation
The copper bromide vapour laser that is a new variant of the copper vapour laser, the most powerful and efficient visible laser, is a Bulgarian invention (Bulg. patent No.:28674, 1975).
Introduction
The copper vapour laser is among the 12 laser sources having found wide practical applications and being of commercial interest. This laser is of particular importance for applications in medicine, industry, navigation, laser isotope separation, speed photography, laser microscopy, laser displays, etc. Many companies have adopted it for industrial production.
The copper vapour laser was created in 1965 by the American scientist William Walter. This laser is the most powerful source of coherent visible radiation. It emits two wavelengths, 511 nm and 578 nm with 1% efficiency. The main problem with copper vapour lasers is the high temperature necessary for the laser active medium where laser action processes take place. This temperature is 1500°C and this makes difficult both the technology for producing reliable laser sources and their practical applying.
Invention
In the beginning of the 70s of the 20th century many research laboratories working on copper lasers, focused their efforts toward the creation of a low temperature variant of the copper vapour laser. The idea to be created such a laser with using some chemical compounds of copper had been suggested still in the first scientific reports by Walter. This idea, however, had turned out to be no easily realizable due to the influence of different chemical elements on laser action processes in the laser active medium. The first experimental results were obtained later. In 1973, American scientists at the Westinghouse laboratories reported laser action with the use of copper iodide. The same year, another American research team at the Pasadena rocket laboratory obtained laser action with the use of copper chloride.
In 1974, a Bulgarian research team guided by N. Sabotinov at the Institute of Solid State Physics, the Bulgarian Academy of Sciences, attained laser action with using copper bromide. This result was patented by N.Sabotinov (Bulgarian patent No.:28674, (1975). Subsequent investigations on the three types of copper halidelaser showed that the output laser powers are mutually correlated as 3:2:1 for the lasers with copper bromide, copper chloride and copper iodide, respectively. These scientific investigations proved that the Bulgarian idea was the most advanced and could be applied in the creation of a low-temperature copper laser. Thus in Bulgaria was set the beginning of profound scientific research aimed at the creation of copper bromide vapour laser with capabilities for practical applications.
Investigations
The first scientific investigations of the copper bromide vapour laser shown that it offered many excellencies over the elemental copper vapour laser. The operating temperature of the active medium is 500°C. The construction of the laser active element, the laser tube, is made of quartz glass without using high-temperature ceramics. Quartz glass is considerably cheaper and easier for technological processing. The copper bromide vapour laser has short warm-up times, 5-10 min., while the copper vapour laser begins to oscillate in no less than 30-40min. after the switch-on. The superiority of the copper bromide vapour laser over the elemental copper vapour laser led to a significant interest in this Bulgarian invention. The research laboratory of metal vapour lasers headed by Prof. Dr. N.Sabotinov, directed its scientific research towards overcoming three essential problems related with the development of the copper bromide vapour laser. These problems included obtaining stable laser generation, achieving long life-times for the laser active element and attaining high output power and efficiency with this new variant of copper laser. The scientific investigations have led to the following important scientific results.
Zones to limit the discharge with using diaphragms in the laser tubes were introduced for the first time. This solution enabled to obtain stable laser action and to extend the lifetime of the copper bromide laser. The idea was patented.
Porous electrodes with reservoirs for bromine and copper bromide were suggested and investigated for the first time. The electrodes remain clean during the time of laser exploitation and maintain a stable discharge regime. The idea was patented and a license was sold.
A copper laser without a pulsed power supply block was realized. The laser tube itself serves as a commutating element. The system works in the regime of relaxing generator.
Molecular dissociation and recombination processes in the copper bromide in the active discharge zone were studied.
A spectral method to control the bromine partial pressure in the laser active zone was developed.
A strong effect of hydrogen in the Ne-CuBr laser was found. It was proved that small admixtures of hydrogen with partial pressures of 0.3-0.5 torr increase twofold the average laser output power and laser efficiency.
Novel electric schemes (IC and ICP) for excitation of the CuBr vapour laser were developed. The novel schemes increase by 40%-50% the output power and efficiency of the CuBrVL.
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Experimental investigation of a CuBr vapour laser
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The kinetics of population of copper atom laser levels in the Ne-CuBr laser active plasma was studied.
Causes limiting the lifetime of the laser active medium were investigated.
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Lifetime testing of CuBr vapour laser tubes
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The influence of bromine concentration on laser action processes were investigated.
A cold zone (-5°C/-8°C) was introduced to control the optimum bromine concentration in the laser active medium. Operating regimes of a CuBr laser MOPA system, including an oscillator and an amplifier, were investigated. An output power of 100W was attained. Results were achieved in the Project NATO SfP-972685 “NATO SfP-Copper Bromide Laser” under the Programme Science for Peace of NATO.Abilities of the CuBr laser active medium to generate maximum specific average output power were investigated. The record output power of 1.4 W/cm3 was achieved. Investigations to achieve maximum average output power were carried out. A record output power of 125 W was obtained at the maximum for copper lasers efficiency of 3%. An efficiency of 3.8% was obtained at 100 W. The results were achieved in the Project CIPA-CT94-0214 of the European Union. Record high beam quality, BQ, M2=1.2-1.5 for lasers emitting in the visible spectrum was achieved. This is very important for the industrial applications of the CuBr laser in precision materials processing. The successful scientific investigations resulted in the achievement of 1%-stability for the laser beam power over 8-hour operation, a lifetime for the laser active element of no less than 1000 h, a record average output power as high as 125 W and a maximum efficiency of 3.8% for the copper lasers.
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40 W CuBr vapour laser beam in the sky of Sofia, 18 April, 2005:
Bulgarian participation in the world light bridge to commemorate the 50th anniversary of Einstein’s death
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Scientific investigations concerning this laser were reported in more than 100 scientific publications in prestigious international journals.
In connection with the development of the copper bromide vapour laser, the laboratory patented still 12 inventions. After the successful scientific investigations, the copper bromide vapour laser in fact has reached a high technological level and readiness for introduction into industrial production.
The invention and the Bulgarian priority in the creation and development of the CuBr laser has been reflected in the international scientific literature including the most extensive monograph on metal vapour lasers, “Metal Vapour Lasers” by Dr. Christopher E. Little, Wiley, 1999.
International acknowledgment of the above described achievements also was received from the survey paper by Prof.C.Webb, a Member of the British Royalty Society. Of particular importance is the attitude of Acad. N.G.Bassov, a Nobel Prize laureate of quantum electronics, about the creation of the copper bromide vapour laser by N.Sabotinov.
The copper bromide vapour laser has gained wide popularity. It is used in different human activities. International conferences sections are organized on the development and the problems of the copper bromide laser. The CuBr laser development is considered to be an essential stage in the development of copper lasers.
Transfers to industry
Introducing the copper bromide vapour laser into the industry of Bulgaria
In order to demonstrate the capabilities of the copper bromide vapour laser for practical applications, in the Laboratory of Metal Vapour Lasers at the Institute of Solid State Physics, BAS, were made two trial samples for work under out-of-laboratory conditions. The invention “Copper bromide vapour laser” wined the prize of BAS for the best invention for 1979. The first steps of the Laboratory for transfer of the copper bromide laser toward industrial production were made jointly with the company Optical Technologies, Plovdiv, Bulgaria.
The copper bromide vapour laser was demonstrated at the Bulgarian stand in the International Technical Fair, Hanover, 1985. The laser attracted the attention of West-European companies producing copper vapour lasers.
A production section for making tubes for copper bromide vapour lasers of up to 10 W output power was organized in the ISSP, BAS in 1988-1990. The tubes made were built into lasers produced as in Bulgaria, so abroad.
Introducing the copper bromide vapour laser into the industry abroad
Interest in acquiring a license for the copper bromide vapour laser was shown by the Australian company Norseld, the American companies Metal Laser Technology and Metal Laser, and the British company Oxford Lasers. Bulgarian scientists carried out successful investigations together with the Australian company Norseld and the American company Metal Laser Technology. These investigations showed the high quality of the Bulgarian invention product. Norseld was selected as the most relevant partner and in 1988 a technology transfer was realized.
Realization of the copper bromide vapour laser today
Today, the copper bromide vapour laser is produced successfully in Bulgaria on the basis of contract relationships between the Laboratory of Metal Vapour Lasers at the ISSP, BAS and the small enterprise Pulslight Co. , Bulgaria. The production of the company Pulslight includes mainly making laser display units, medical laser systems and laser industrial systems for precision processing of materials. The output powers of the lasers made by the company are in the range 2-100 W depending on the model. The Bulgarian company Pulslight produces lasers for the Bulgarian market and also exports production to the USA, Mexico, Canada, Germany, Poland, Italy, Cyprus, Romania, and so on.
Another two Bulgarian companies also produce lasers and laser systems on the basis of the copper bromide vapour laser invented by Prof.N.Sabotinov. The one is Laser Product, which works in close cooperation with Pulslight, and the other is Spektronika, which produces low-power lasers, mainly for laser displays.
The Australian company Norseld which continues its contacts with the research team of Prof. N. Sabotinov, has successfully realized its copper bromide vapour laser products on the markets of the USA, Europe and Asia. The main applications of the copper bromide vapour lasers produced by this company are in medicine, dermatology and industry for precision materials processing. The cooperation of Bulgarian researchers with the Australian company Norseld is an example of successful introduction of a Bulgarian technology into foreign industry.
At present, the research team guided by Prof.N.Sabotinov is continuing investigations related with the development of copper bromide vapour lasers and is working on the creation of a powerful laser with high beam quality for precision material processing for industry. These scientific investigations are well financed by scientific programmes of the European Union and NATO.
The development of the copper bromide laser has been financed by the Project No.: CIPA-CT940214 “New Generation Lasers for High Precision Materials Processing” under the FP4 of the European Union. Participating countries in this project were Great Britain, Bulgaria and Poland. The total budget of the Project was 300,000 EUR as for Bulgaria were 90,200 EUR.
The creation of a high-power copper bromide vapour was financed by the Project NATO SfP-972685 “NATO SfP-Copper Bromide Laser”, entitled “Development of a System Based on a High Power and High Efficiency Copper Bromide Laser for Precision Materials Processing”. Project partners were from Germany, Italy, Bulgaria and Poland. The total budget for the Project was 275,191EUR, for Bulgaria: 91,940 EUR.
Applications of the copper bromide laser
- Medicine: The copper bromide laser yellow radiation is used in dermatology for photocoagulation
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| Dual yellow laser [Norseld Pty Ltd ] |
- Industry: for drilling, cutting, marking
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80-Watt CuBr vapour laser MOPA system for material processing [ Pulslight Ltd. ] |
- Laser navigation, laser microscopy, scientific studies
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| Studying atmosphere parameters with a CuBr vapour laser |