Multiple-prism grating laser oscillator

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Multiple-prism grating laser oscillators, [1] or MPG laser oscillators, use multiple-prism beam expansion to illuminate a diffraction grating mounted either in Littrow configuration or grazing-incidence configuration. Originally, these narrow-linewidth tunable dispersive oscillators were introduced as multiple-prism Littrow (MPL) grating oscillators, [2] or hybrid multiple-prism near-grazing-incidence (HMPGI) grating cavities, [3] [4] in organic dye lasers. However, these designs were quickly adopted for other types of lasers such as gas lasers, [5] [6] diode lasers, [7] [8] and more recently fiber lasers. [9]

Beam expanders are optical devices that take a collimated beam of light and expand its size.

Optical cavity arrangement of mirrors that forms a standing wave cavity resonator for light waves

An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric oscillators and some interferometers. Light confined in the cavity reflects multiple times producing standing waves for certain resonance frequencies. The standing wave patterns produced are called modes; longitudinal modes differ only in frequency while transverse modes differ for different frequencies and have different intensity patterns across the cross section of the beam.

Dye laser

A dye laser is a laser which uses an organic dye as the lasing medium, usually as a liquid solution. Compared to gases and most solid state lasing media, a dye can usually be used for a much wider range of wavelengths, often spanning 50 to 100 nanometers or more. The wide bandwidth makes them particularly suitable for tunable lasers and pulsed lasers. The dye rhodamine 6G, for example, can be tuned from 635 nm (orangish-red) to 560 nm (greenish-yellow), and produce pulses as short as 16 femtoseconds. Moreover, the dye can be replaced by another type in order to generate an even broader range of wavelengths with the same laser, from the near-infrared to the near-ultraviolet, although this usually requires replacing other optical components in the laser as well, such as dielectric mirrors or pump lasers.

Contents

Multiple-prism grating narrow-linewidth tunable laser oscillator. The grating in this particular oscillator is deployed in Littrow configuration. Duarte's multiple-prism grating laser oscillator.png
Multiple-prism grating narrow-linewidth tunable laser oscillator. The grating in this particular oscillator is deployed in Littrow configuration.

Excitation

Multiple-prism grating laser oscillators can be excited either electrically, as in the case of gas lasers and semiconductor lasers, [11] or optically, as in the case of crystalline lasers and organic dye lasers. [1] In the case of optical excitation it is often necessary to match the polarization of the excitation laser to the polarization preference of the multiple-prism grating oscillator. [1] This can be done using a polarization rotator thus improving the laser conversion efficiency. [11]

Polarization rotator

A polarization rotator is an optical device that rotates the polarization axis of a linearly polarized light beam by an angle of choice. Such devices can be based on the Faraday effect, on birefringence, or on total internal reflection. Rotators of linearly polarized light have found widespread applications in modern optics since laser beams tend to be linearly polarized and it is often necessary to rotate the original polarization to its orthogonal alternative.

Linewidth performance

The multiple-prism dispersion theory is applied to design these beam expanders either in additive configuration, thus adding or subtracting their dispersion to the dispersion of the grating, or in compensating configuration (yielding zero dispersion at a design wavelength) thus allowing the diffraction grating to control the tuning characteristics of the laser cavity. [11] Under those conditions, that is, zero dispersion from the multiple-prism beam expander, the single-pass laser linewidth is given by [1] [11]

Multiple-prism dispersion theory Theory in optics

The first description of multiple-prism arrays, and multiple-prism dispersion, was given by Newton in his book Opticks. Prism pair expanders were introduced by Brewster in 1813. A modern mathematical description of the single-prism dispersion was given by Born and Wolf in 1959. The generalized multiple-prism dispersion theory was introduced by Duarte and Piper in 1982.

Laser linewidth is the spectral linewidth of a laser beam.

where is the beam divergence and M is the beam magnification provided by the beam expander that multiplies the angular dispersion provided by the diffraction grating. In the case of multiple-prism beam expanders this factor can be as high as 100-200. [1] [11]

When the dispersion of the multiple-prism expander is not equal to zero, then the single-pass linewidth is given by [1] [11]

where the first differential refers to the angular dispersion from the grating and the second differential refers to the overall dispersion from the multiple-prism beam expander. [1] [11]

Optimized solid-state multiple-prism grating laser oscillators have been shown, by Duarte, to generate pulsed single-longitudinal-mode emission limited only by Heisenberg's uncertainty principle. [12] The laser linewidth in these experiments is reported as ≈ 350 MHz (or ≈ 0.0004 nm at 590 nm) in pulses ~ 3 ns wide, at power levels in the kW regime. [12]

Applications

Applications of these tunable narrow-linewidth lasers include:

See also

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Prism transparent optical element with flat, polished surfaces that refract light

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Tunable laser

A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength range.

Atomic vapor laser isotope separation

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Fiber Bragg grating

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Prism compressor optical device used to shorten the duration of a positively chirped ultrashort laser pulse

A prism compressor is an optical device used to shorten the duration of a positively chirped ultrashort laser pulse by giving different wavelength components a different time delay. It typically consists of two prisms and a mirror. Figure 1 shows the construction of such a compressor. Although the dispersion of the prism material causes different wavelength components to travel along different paths, the compressor is built such that all wavelength components leave the compressor at different times, but in the same direction. If the different wavelength components of a laser pulse were already separated in time, the prism compressor can make them overlap with each other, thus causing a shorter pulse.

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Free spectral range (FSR) is the spacing in optical frequency or wavelength between two successive reflected or transmitted optical intensity maxima or minima of an interferometer or diffractive optical element.

F. J. Duarte Chilean-American physicist

Francisco Javier "Frank" Duarte is a laser physicist and author/editor of several well-known books on tunable lasers and quantum optics. He introduced the generalized multiple-prism dispersion theory, has discovered various multiple-prism grating oscillator laser configurations, and pioneered polymer-nanoparticle gain media. His contributions have found applications in a variety of fields including astronomical instrumentation, atomic vapor laser isotope separation, geodesics, gravitational lensing, laser medicine, laser microscopy, laser pulse compression, laser spectroscopy, nonlinear optics, and tunable diode lasers.

Fritz Peter Schäfer was a German physicist, born in Hersfeld, Hesse-Nassau. He is the co-inventor of the organic dye laser. His book, Dye Lasers, is considered a classic in the field of tunable lasers. In this book the chapter written by Schäfer gives an ample and insightful exposition on organic laser dye molecules in addition to a description on the physics of telescopic, and multiple-pism, tunable narrow-linewidth laser oscillators.

Quantum mechanics was first applied to optics, and interference in particular, by Paul Dirac. Richard Feynman, in his Lectures on Physics, uses Dirac's notation to describe thought experiments on double-slit interference of electrons. Feynman's approach was extended to N-slit interferometers for either single-photon illumination, or narrow-linewidth laser illumination, that is, illumination by indistinguishable photons, by Frank Duarte. The N-slit interferometer was first applied in the generation and measurement of complex interference patterns.

Solid-state dye lasers

Solid-state dye lasers (SSDL) were introduced in 1967 by Soffer and McFarland. In these solid-state lasers, the gain medium is a laser dye-doped organic matrix such as poly(methyl methacrylate) (PMMA), rather than a liquid solution of the dye. An example is rhodamine 6G-doped PMMA. These lasers are also referred to as solid-state organic lasers and solid-state dye-doped polymer lasers.

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James A. (Jim) Piper is a New Zealand/Australian physicist, Deputy Vice-Chancellor (Research) and Professor of Physics at Macquarie University.

Organic laser

Organic lasers use an organic material as the gain medium. The first organic laser was the liquid dye laser. These lasers use laser dye solutions as their gain media.

References

  1. 1 2 3 4 5 6 7 F. J. Duarte, Narrow-linewidth pulsed dye laser oscillators, in Dye Laser Principles (Academic, New York, 1990) Chapter 4.
  2. ↑ F. J. Duarte and J. A. Piper, A double-prism beam expander for pulsed dye lasers, Opt. Commun.35, 100-104 (1980).
  3. ↑ F. J. Duarte and J. A. Piper, A prism preexpanded grazing incidence pulsed dye laser, Appl. Opt.20, 2113-2116 (1981).
  4. ↑ F. J. Duarte and J. A. Piper, Narrow linewidth high prf copper laser-pumped dye-laser oscillators, Appl. Opt.23, 1391-1394 (1984).
  5. ↑ F. J. Duarte, Multiple-prism Littrow and grazing incidence pulsed CO2 lasers, Appl. Opt.24, 1244-1245 (1985).
  6. ↑ R. C. Sze and D. G. Harris, Tunable excimer lasers, in Tunable Lasers Handbook, F. J. Duarte (Ed.) (Academic, New York, 1995) Chapter 3.
  7. ↑ P. Zorabedian, Characteristics of a grating-external-cavity semiconductor laser containing intracavity prism beam expanders, J. Lightwave Tech.10, 330–335 (1992).
  8. ↑ P. Zorabedian, Tunable external cavity semiconductor lasers, in Tunable Lasers Handbook, F. J. Duarte (Ed.) (Academic, New York, 1995) Chapter 8.
  9. ↑ T. M. Shay and F. J. Duarte, in Tunable Laser Applications, 2nd Ed., F. J. Duarte (Ed.) (CRC, New York, 2009) Chapter 9.
  10. ↑ F. J. Duarte, T. S. Taylor, A. Costela, I. Garcia-Moreno, and R. Sastre, Long-pulse narrow-linewidth disperse solid-state dye laser oscillator, Appl. Opt.37, 3987–3989 (1998).
  11. 1 2 3 4 5 6 7 F. J. Duarte, Tunable Laser Optics, 2nd Ed. (CRC, New York, 2015).
  12. 1 2 F. J. Duarte, Multiple-prism grating solid-state dye laser oscillator: optimized architecture, Appl. Opt.38, 6347-6349 (1999).
  13. ↑ R. J. Hall and A. C. Eckbreth, Coherent anti-Stokes Raman spectroscopy: applications to combustion diagnostics, in Laser Applications (Academic, New York, 1984) pp. 213-309.
  14. ↑ W. B. Grant, Lidar for atmospheric and hydrospheric studies, in Tunable Laser Applications, 1st Ed. (Marcel-Dekker, New York, 1995) Chapter 7.
  15. ↑ W. Demtröder, Laserspektroscopie: Grundlagen und Techniken, 5th Ed. (Springer, Berlin, 2007).
  16. ↑ W. Demtröder, Laser Spectroscopy: Basic Principles, 4th Ed. (Springer, Berlin, 2008).
  17. ↑ S. Singh, K. Dasgupta, S. Kumar, K. G. Manohar, L. G. Nair, U. K. Chatterjee, High-power high-repetition-rate capper-vapor-pumped dye laser, Opt. Eng.33, 1894-1904 (1994).
  18. ↑ A. Sugiyama, T. Nakayama, M. Kato, Y. Maruyama, T. Arisawa, Characteristics of a pressure-tuned single-mode dye laser oscillator pumped by a copper vapor oscillator, Opt. Eng.35, 1093-1097 (1996).
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