Abstract
The beam pointing of a multi-terawatt laser wave laser is stabilized on a millisecond time scale using an active control system. Two piezo mirrors, two position sensing detectors, and a computer based optimization program ensure that both near- and far-field are stable, even during single shot operation. A standard deviation for the distribution of laser shots of 2.6 μ rad is achieved.
| Original language | English |
|---|---|
| Article number | 033102 |
| Journal | Review of Scientific Instruments |
| Volume | 82 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - 1 Jan 2011 |
| MoE publication type | Not Eligible |
Funding
The authors would like to acknowledge the fruitful discussions and collaboration within Lund University with L. Österman, B. Lundberg, B. Wittenmark, K. J. Åström, A. Cervin, and L. Sörnmo. The authors acknowledge the financial support from the Swedish Research Council and the Knut and Alice Wallenberg Foundation. This research was supported by the Marie Curie Early Stage Training Site MAXLAS (Contract No. MEST-CT-2005-020356) within the 6th European Community Framework Programme and the NEST Activity under the FP6 Structuring the European Research Area programme (project EuroLEAP, Contract No. 028514). FIG. 1. Schematic view of the beam pointing stabilization system of the Lund Laser Centre multi-TW laser (details in the text). The inset shows a side view of the injection point of the reference beam. The system works in the following way: two piezo mirrors are compensating for fluctuations in the beam pointing, one controls the near-field and other the far-field. Right before a main laser pulse arrives, the mirrors are fixed while fast shutters close to protect the detectors from the high power laser pulse. Once the laser pulse has passed the shutters open and the system starts regulating again. FIG. 2. (a) Typical step responses of the system. The gray and black curves are the signals recorded by the horizontal axis of the PSDs monitoring the far-field and near-field, respectively. In (b) the timing of the fast shutter used to protect the detectors is described. The black line shows the intensity recorded by the PSD and the gray line is the voltage sent to the piezo mirror. The dashed line corresponds to the time when the TW laser pulse arrives. FIG. 3. Filtering of the laser shots is necessary to avoid the short but intense burst of high frequency vibrations produced by the cryogenic cooler. The main shutter of the laser delivers shots only when the vibrations are minimal. FIG. 4. Pointing of 200 consecutive laser shots recorded by a microscope objective and a CCD camera. On the right side corresponding distributions of deviations from the mean. In (a) and (b) no active stabilization is used, in (c) and (d) the laser shots are gated in time in order to avoid firing when intense vibrations are produced by the cryogenic cooler in the laser amplifier. Finally, in (e) and (f), active stabilization is added with the help of two piezo mirrors. The circle represents the deviation corresponding to one standard deviation and its radius decreases for each step of the stabilization. FIG. 5. Near-field position of the reference beam for 200 consecutive shots recorded by a CCD camera imaging the position of the beam on the focusing optics. In (a) no active stabilization is used and in (b) the active stabilization is added.
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