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Laser alignment servo method and apparatus
| Details |
Inventors: Hobart, James L.; Mefferd, Wayne S.; Peuse, Bruce;
Assignee: Coherent, Inc. (Palo Alto, CA)
Primary Examiner: Scott, Jr.; Leon
Assistant Examiner:
Attorney, Agent or Firm: Limbach, Limbach & Sutton
A servo alignment method and apparatus for maintaining laser beam alignment. An operating parameter of the laser (such as output beam power) is measured, and error signals are generated from the measured operating parameter signal for controlling the laser beam alignment. In one class of embodiments, modulation signals are supplied to an intra-cavity component of a laser system to modulated the beam path. The beam path may be modulated by reciprocating a laser resonator mirror about a mirror axis or two substantially orthogonal mirror axes. In the latter case, the mirror may be vibrated about the axes either alternately (first about one axis and then about the other) or simultaneously. In embodiments in which an intra-cavity component is modulated, the laser operating parameter is measured during such modulation, the measured operating parameter signal is demodulated (preferably by multiplication in a mixer with a selected frequency component of the modulation signal currently being asserted), and error signals are generated from the demodulated signal for controlling the laser beam alignment. |
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DETAILED DESCRIPTION The invention is a servo method and apparatus for maintaining laser beam alignment.
An operating parameter of the laser (such as output beam power) is measured, and error signals are generated from the measured operating parameter signal for controlling the laser beam alignment.
In one class of embodiments, modulation signals are supplied to an intra-cavity component of a laser system (such as a laser resonator mirror) to modulate the beam path.
The beam path may be modulated by reciprocating a laser resonator mirror about an axis or two substantially orthogonal axes.
In the latter case, the mirror may be vibrated about the axes either alternately (first about one axis and then about the other) or simultaneously.
In embodiments in which an intra-cavity component is modulated, the laser operating parameter is measured during such modulation, the measured operating parameter signal is demodulated (preferably by multiplication in a mixer with a selected frequency component of the modulation signal currently being asserted), and error signals are generated from the demodulated signal for controlling the laser beam alignment.
In one example, transducers reciprocate a laser resonator mirror about two orthogonal mirror axes while an error signal is generated for each axis, the error signals are then integrated, and the integrated error signals are then supplied to the transducers to tip the mirror into an optimal orientation (an orientation achieving optimal laser beam alignment).
One preferred embodiment includes a pair of transducers for independently controlling the alignment of a resonator mirror about either of a pair of orthogonal axes (sometimes referred to herein as horizontal and vertical axes), and mirror modulation signals are alternately supplied to the transducers.
Each mirror modulation signal has a DC component and a time varying component having frequency f.
sub.
0 (for example, a 15 Hz square wave).
A photodetector monitors the laser output beam power, and a band pass filter is provided for filtering the analog output signal from the photodetector
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