Glass - Back to the Future!



Presenting Author:
Elena Krekhova
<e.krehova@mail.ru>

article posted 05 Jan 2016


Elena Krekhova is a Leading Engineer Technologist at Lytkarino Optical Glass Factory in Moscow, and she is also a Senior Lecturer at the Moscow Technical University.

Her PhD was awarded in 2000 for research in the chemical technology of refractory non-metallic materials at the University of Chemical Technology of Russia in Moscow.






Defining of the damage threshold of optical materials, used as
laser active medium with the help of a new system

Y.A. Kalinin1, E.Y. Krekhova2*, A.E. Pozdnyakov2, D.A. Khramogin2


Further development of glasses application as laser active medium is restricted by their insufficient damage threshold. That's why development of reliable tools for testing the glasses for their damage threshold remains vital. This report describes the main principles of constructing the measuring facilities for testing the glasses for their damage threshold and the experience of developing a such system for testing of laser phosphate glass samples.

It is known that the beam damage threshold of materials under testing depends on the following: equivalent area exposed to radiation (Seq); duration of radiation impulse, statistic character of destruction process. These factors were considered while developing the damage threshold measurement system.

Apart from that, application conditions of glasses were considered. In case the maximum radiation density on the amplifier active elements are approximately 10 J/cm2, the strength margin should be 2~3 times, i.e. the value of beam strength threshold is established at the level of 30 J/cm2. This value defined the energetic parameters. Apart from that, the system should be characterized by operational wave length - 1054 nm and radiation impulse duration - 3~5 ns.

In the paper presented hereby, the laser system for damage threshold measurement is built using standard schematic used for systems operating in nanosecond range of impulse durations (ref. Fig 1a, 1b).


Figure 1a: General view of the laser system - amplifier cascades


Figure 1b: General view of the laser system - system of radiation focusing



The system specific feature is the potential of increasing the radiation energy (increase coefficient is not less than 10 000) and creating the sample equivalent zone of exposure with the uniform distribution of radiation density in a spot of quite large dimensions 5x5 mm while using the low power generator (ref. Fig 2).




Figure 2: Profile of the focused radiation beam




Threshold energy density (damage threshold) for series of phosphate glass disc active elements witness samples, obtained through various manufacturing processes, was measured using the newly made system. The resulting data allowed choosing the optimal manufacturing process ensuring the required beam strength value - not less than 30 J/cm2. The measurement error came to 8 % with quantity of sample exposures to radiation 8~10 times.

Institutions:

1 JSC Shvabe-Issledovaniya, Volokolamskoe shosse, H. 112, b1,c.3, Moscow, 125424, Russia; <kalin-yurij@yandex.ru>

2 JSC LZOS, H.1, Parkovay str., Lytkarino, 140080, Russia <npk-74@lzos.ru>