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Optics Letters

Optics Letters


  • Vol. 25, Iss. 5 — Mar. 1, 2000
  • pp: 311–313

Cancellation of laser dither modulation from optical frequency standards

Matthew S. Taubman and John L. Hall  »View Author Affiliations

Optics Letters, Vol. 25, Issue 5, pp. 311-313 (2000)

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We demonstrate the removal of the dither modulation from an iodine-stabilized He–Ne laser by using a frequency-modulated acousto-optic modulator and feed-forward techniques. This procedure reduces the linewidth of the beat between this laser and a flywheel He–Ne laser from 6 MHz to 8 kHz, the undithered beat linewidth being ∼7 kHz. Dither suppression greatly reduces counter errors during beat measurements from stroboscopic effects between the counter's gate and the frequency of the dither modulation and increases the utility of the already formidable array of dithered laser frequency standards by making locking to them an easier task.

© 2000 Optical Society of America

OCIS Codes
(000.2170) General : Equipment and techniques
(120.3940) Instrumentation, measurement, and metrology : Metrology
(120.5060) Instrumentation, measurement, and metrology : Phase modulation

Matthew S. Taubman and John L. Hall, "Cancellation of laser dither modulation from optical frequency standards," Opt. Lett. 25, 311-313 (2000)

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  1. T. J. Quinn, Metrologia 30, 524 (1994).
  2. A. J. Wallard, J. Phys. E 5, 926 (1972); J. L. Hall, G. Kramer, and R. L. Barger, in Conference on Precision Electro Magnetic Measurement Digest 1972 (Institute of Electrical and Electronics Engineers, New York, 1972), p. 75.
  3. Early digital frequency counters typically accumulate the number of positive zero crossings in a set time, giving correct counts but limited precision. A newer design (HP53132A) has vastly higher resolution by using a random sampling. At carrier frequencies above 50 MHz this strategy works even with the 6-MHz peak-to-peak FM discussed in this Letter. But, at much below this carrier frequency, such deep FM causes erratic operation, giving errors of many megahertz.
  4. M. L. Eickhoff and J. L. Hall, IEEE Trans. Instrum. Meas. 44, 155 (1995).
  5. See Ref. 1. For example, the Comité Consultatif du Longeur (CCL, formerly CCDM) has recommended values for five He–Ne laser lines and one argon-ion laser line locked to several lines in I2 by dither-locking techniques.
  6. The unit used was Model 925A from Berkeley Nucleonics. This information is provided for technical communication purposes only and does not constitute an endorsement by the National Institute of Standards and Technology or the University of Colorado.
  7. Feedback alone could in theory cancel such FM and was in fact tried with the goal of inherently correcting for the nonlinearity of the AOM driver. However, the noise performance of feedback was found to be far inferior to feed forward, because to have a useful gain of G at modulation frequency f a required feedback servo bandwidth of greater than Gf brings added noise across this entire frequency region. Feed forward can provide exact cancellation of a known perturbation with essentially no bandwidth and hence practically zero added noise.
  8. M. S. Taubman and J. L. Hall, “Precise removal from a laser beam of large frequency modulations generated either internally or externally to the laser,” Provisional Application No. 60/134, 884, May 19, 1994.

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