A high stability TEA CO2 laser system, P.N.D. Maggs, Electro-Optic Laser International, '76 UK
This was the first scientific paper I did on my own. When I had completed my three year studentship (1974), the PhD work was far from finished. I was offered a two year post doctoral research fellowship at Essex University, care of good old Alan Gibson. Apart from some teaching, the main task was to construct a high-stability laser system that would be eventually transported to Heriot Watt university in Edinburgh. In parallel, I was able to finish the research work.
In designing the laser system, I attempted to bring together all the current (1974) knowledge and experience of TEA laser design in order to address as many of the practical difficulties of using TEA CO2 lasers to perform useful tasks.
There were three major drawbacks with TEA CO2 lasers at the time: 1) optical mode beating resulting in substantial changes pulse to pulse in peak power and pulse shape; 2) the enormous amount of RF ‘noise’ generated by the high voltage discharge and 3) the low repetition rate available from many systems – generally not more than one or two pulses per second.
The paper describes an excellent method for overcoming the first problem using a low pressure discharge tube, and the results were really good. The downside of this, was that the laser cavity became very long – the high and low pressure systems were optically in series, making a system length of seven or eight feet. To provide laser output at a high repetition rate – 100 pulses per second were chosen – I built a totally overdesigned wind-tunnel in Perspex in order to transport the laser gas – carbon dioxide, helium and nitrogen – through the discharge region at a rate ensuring that the gas was changed many times between pulses. The electrical double-discharge system used a pair of thyratron switches made by EEV in Chelmsford.
The cavity length and the size of the wind-tunnel assembly made resolving the second problem – RF noise – really difficult. There is an excellent and time-honoured method for supressing RF noise, simply enclose the noise source in a Faraday Cage – a box with electrically conducting walls, floor and ceiling. This is what was done, but the resulting structure – a steel frame covered with sheet steel panels – was a monster. It was eight or nine feet long, six feet high and around four feet deep. Getting it to Edinburgh in a Luton Van was a nightmare.
But it did work, and the paper describes the results. The laser certainly accomplished all of the initial objectives, but an engineering masterpiece it definitely was not.
Click below to read the paper...
This was the first scientific paper I did on my own. When I had completed my three year studentship (1974), the PhD work was far from finished. I was offered a two year post doctoral research fellowship at Essex University, care of good old Alan Gibson. Apart from some teaching, the main task was to construct a high-stability laser system that would be eventually transported to Heriot Watt university in Edinburgh. In parallel, I was able to finish the research work.
In designing the laser system, I attempted to bring together all the current (1974) knowledge and experience of TEA laser design in order to address as many of the practical difficulties of using TEA CO2 lasers to perform useful tasks.
There were three major drawbacks with TEA CO2 lasers at the time: 1) optical mode beating resulting in substantial changes pulse to pulse in peak power and pulse shape; 2) the enormous amount of RF ‘noise’ generated by the high voltage discharge and 3) the low repetition rate available from many systems – generally not more than one or two pulses per second.
The paper describes an excellent method for overcoming the first problem using a low pressure discharge tube, and the results were really good. The downside of this, was that the laser cavity became very long – the high and low pressure systems were optically in series, making a system length of seven or eight feet. To provide laser output at a high repetition rate – 100 pulses per second were chosen – I built a totally overdesigned wind-tunnel in Perspex in order to transport the laser gas – carbon dioxide, helium and nitrogen – through the discharge region at a rate ensuring that the gas was changed many times between pulses. The electrical double-discharge system used a pair of thyratron switches made by EEV in Chelmsford.
The cavity length and the size of the wind-tunnel assembly made resolving the second problem – RF noise – really difficult. There is an excellent and time-honoured method for supressing RF noise, simply enclose the noise source in a Faraday Cage – a box with electrically conducting walls, floor and ceiling. This is what was done, but the resulting structure – a steel frame covered with sheet steel panels – was a monster. It was eight or nine feet long, six feet high and around four feet deep. Getting it to Edinburgh in a Luton Van was a nightmare.
But it did work, and the paper describes the results. The laser certainly accomplished all of the initial objectives, but an engineering masterpiece it definitely was not.
Click below to read the paper...
| tea_co2_laser_system.pdf |