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Laser Noise

Definition: fluctuations of various parameters of laser light, such as the optical power and phase

More specific terms: intensity noise, phase noise, timing jitter

German: Laserrauschen

Categories: lasers, fluctuations and noise

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Due to various influences of quantum noise and fluctuations of various technical origins, the output of a laser always contains some noise. There are different kinds of laser noise:

Origins of Laser Noise

The origins of laser noise can be divided into two groups:

  • quantum noise, in particular associated with spontaneous emission in the gain medium
  • technical noise, arising e.g. from excess noise of the pump source, from vibrations of the laser resonator, or from temperature fluctuations

Impacts of Laser Noise

Laser noise is important for many laser applications. Some examples are:

intensity noise spectrum
Figure 1: Intensity noise spectrum of a solid-state laser.

Methods for Noise Reduction

Laser noise can be reduced in many ways:

  • Quantum noise can be reduced e.g. by increasing the intracavity power level and by minimizing optical losses.
  • Technical noise influences can be reduced, e.g. by building a stable laser resonator, by temperature stabilization of the setup, or by using a low-noise pump source.
  • Laser parameters can be optimized so that the laser reacts less strongly to certain noise influences.
  • Mode hopping may be suppressed, e.g. with an optical filter.
  • There are various active or passive techniques for the stabilization of lasers.

A prerequisite for effective noise reduction is that the origin of the most disturbing noise is known, in addition to the parameters determining the laser's sensitivity to thus noise influences. Depending on the case, it can be more effective to reduce either noise influences themselves or the laser's sensitivity.

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Suppliers

The RP Photonics Buyer's Guide contains 5 suppliers for laser noise measurement equipment.

Bibliography

[1]A. L. Schawlow and C. H. Townes, “Infrared and optical masers”, Phys. Rev. 112 (6), 1940 (1958), doi:10.1103/PhysRev.112.1940
[2]C. C. Harb et al., “Intensity-noise dependence of Nd:YAG lasers on their diode-laser pump source”, J. Opt. Soc. Am. B 14 (11), 2936 (1997), doi:10.1364/JOSAB.14.002936
[3]B. C. Buchler et al., “Feedback control of laser intensity noise”, Phys. Rev. A 57 (2), 1286 (1998), doi:10.1103/PhysRevA.57.1286
[4]T. C. Ralph et al., “Understanding and controlling laser intensity noise”, Opt. Quantum Electron. 31, 583 (1999), doi:10.1023/A:1006943801659
[5]R. Paschotta, “Noise of mode-locked lasers. Part I: numerical model”, Appl. Phys. B 79, 153 (2004); R. Paschotta, “Noise of mode-locked lasers. Part II: timing jitter and other fluctuations”, Appl. Phys. B 79, 163 (2004), doi:10.1007/s00340-004-1548-9
[6]R. Paschotta et al., “Optical phase noise and carrier–envelope offset noise of mode-locked lasers”, Appl. Phys. B 82 (2), 265 (2006), doi:10.1007/s00340-005-2041-9
[7]R. Paschotta, H. R. Telle, and U. Keller, “Noise of Solid State Lasers”, in Solid-State Lasers and Applications (ed. A. Sennaroglu), CRC Press, Boca Raton, FL (2007), Chapter 12, pp. 473–510
[8]R. Paschotta, “Noise in Laser Technology”. Part 1 – Intensity and Phase Noise; Part 2: Fluctuations in Pulsed Lasers; Part 3: Beam Pointing Fluctuations

(Suggest additional literature!)

See also: noise specifications, laser specifications, quantum noise, shot noise, intensity noise, phase noise, linewidth, Schawlow–Townes linewidth, amplifier noise, coherence, stabilization of lasers, mode hopping, The Photonics Spotlight 2006-08-01, The Photonics Spotlight 2006-08-20, The Photonics Spotlight 2006-10-09
and other articles in the categories lasers, fluctuations and noise

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