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Control of Laser Focusing using a Deformable Mirror and a Genetic Algorithm

Lundh, Olle LU (2003) In Lund Reports on Atomic Physics
Abstract
In this thesis an adaptive optics system has been developed, implemented and evaluated at the Lund High Power Laser facility, Atomic Physics Division, Lund Institute of Technology. The laser system delivers ultrashort pulses with peak powers exceeding 40 TW at a repetition rate of 10 Hz. The pulses are focused to achieve extreme irradiance exceeding 1019 W/cm2 . In order to increase the peak intensity at the focal spot it is possible to either increase the pulse energy, to reduce the pulse length or to make the focal spot smaller. Cost and the laser bandwidth put limits to the two first alternatives. This thesis explores the third option.

The aim for this project was to investigate the abilities of an adaptive optics system to... (More)
In this thesis an adaptive optics system has been developed, implemented and evaluated at the Lund High Power Laser facility, Atomic Physics Division, Lund Institute of Technology. The laser system delivers ultrashort pulses with peak powers exceeding 40 TW at a repetition rate of 10 Hz. The pulses are focused to achieve extreme irradiance exceeding 1019 W/cm2 . In order to increase the peak intensity at the focal spot it is possible to either increase the pulse energy, to reduce the pulse length or to make the focal spot smaller. Cost and the laser bandwidth put limits to the two first alternatives. This thesis explores the third option.

The aim for this project was to investigate the abilities of an adaptive optics system to precompensate for alignment or intrinsic optical errors that would degrade the focusing power of the laser system. A test system, using a smaller deformable mirror than required for the main laser system was developed and implemented by the author and comprise a deformable mirror, a detection system and an optimization algorithm. The deformable mirror was a Micromachined Membrane Deformable Mirror (MMDM), it had 37 electrostatic actuators and was coated with gold. The detection system measured the focal spot peak intensity and the mirror shape was optimized by a Genetic Algorithm (GA). Heavily astigmatic foci were routinely corrected and the MMDM was used to precompensate for the astigmatic errors introduced by off-axis focusing with a spherical mirror. At an off-axis angle of 17o , the focal spot size was improved from 6.5 to 1.3 times the diffraction limit. When the laser was focused with a well aligned parabolic mirror, the algorithm and the deformable mirror were still able to increase the focal spot peak intensity by 85%. The deformable mirror was also used to manipulate the focal spot intensity profile. Multiple

focal spots of equal intensity were successfully generated from a single beam and a scheme that would allow tailored focal spots was tested. (Less)
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Lund Reports on Atomic Physics
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83 pages
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  • other:LRAP-315
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English
LU publication?
yes
id
45e141d8-7354-4d19-b38e-ac6bda17fe91 (old id 1894498)
date added to LUP
2011-04-19 19:08:25
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@techreport{45e141d8-7354-4d19-b38e-ac6bda17fe91,
  abstract     = {In this thesis an adaptive optics system has been developed, implemented and evaluated at the Lund High Power Laser facility, Atomic Physics Division, Lund Institute of Technology. The laser system delivers ultrashort pulses with peak powers exceeding 40 TW at a repetition rate of 10 Hz. The pulses are focused to achieve extreme irradiance exceeding 1019 W/cm2 . In order to increase the peak intensity at the focal spot it is possible to either increase the pulse energy, to reduce the pulse length or to make the focal spot smaller. Cost and the laser bandwidth put limits to the two first alternatives. This thesis explores the third option.<br/><br>
The aim for this project was to investigate the abilities of an adaptive optics system to precompensate for alignment or intrinsic optical errors that would degrade the focusing power of the laser system. A test system, using a smaller deformable mirror than required for the main laser system was developed and implemented by the author and comprise a deformable mirror, a detection system and an optimization algorithm. The deformable mirror was a Micromachined Membrane Deformable Mirror (MMDM), it had 37 electrostatic actuators and was coated with gold. The detection system measured the focal spot peak intensity and the mirror shape was optimized by a Genetic Algorithm (GA). Heavily astigmatic foci were routinely corrected and the MMDM was used to precompensate for the astigmatic errors introduced by off-axis focusing with a spherical mirror. At an off-axis angle of 17o , the focal spot size was improved from 6.5 to 1.3 times the diffraction limit. When the laser was focused with a well aligned parabolic mirror, the algorithm and the deformable mirror were still able to increase the focal spot peak intensity by 85%. The deformable mirror was also used to manipulate the focal spot intensity profile. Multiple<br/><br>
focal spots of equal intensity were successfully generated from a single beam and a scheme that would allow tailored focal spots was tested.},
  author       = {Lundh, Olle},
  institution  = {[Publisher information missing]},
  language     = {eng},
  pages        = {83},
  series       = {Lund Reports on Atomic Physics},
  title        = {Control of Laser Focusing using a Deformable Mirror and a Genetic Algorithm},
  year         = {2003},
}