Beam expanders

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Beam expanders are optical devices that pick up a collimated light beam and enlarge its cross-section (or vice versa).

In laser physics , they are used either as intracavity or extracavity elements. They can be telescopic or prismatic in nature . In general, prismatic beam expanders use multiple prisms and are known as multiple prism beam expanders.

Telescopic beam expanders can be based on either refractive lenses ( refractors ) or mirrors ( reflectors ). A commonly used refractive telescope is the Galilean telescope , which can act as a simple beam expander for collimated light. The main advantage of the Galilean construction is that the beam within the optical beam path is nowhere focused to a point, so that the effect that at a very high power density (z. B. dielectric breakdown) are connected, are more easily avoided than with focusing drafts like the Kepler telescope. When used as intracavity beam expanders in laser resonators , these telescopes offer a two-dimensional beam expansion in the range of 20 to 50.

In tunable laser resonators , the intracavity beam expansion typically illuminates the entire width of a diffraction grating . The beam expansion thus reduces the beam divergence and allows the emission very narrow line widths , which for many analytical applications, including laser spectroscopy is a desired feature.

Multiple prism beam expanders

Tunable long pulse laser oscillator using a multiple prism beam expander

Multi-prism beam expanders typically employ two to five prisms to achieve large one-dimensional beam expansion factors. Designs applicable to tunable lasers with beam expansion factors of up to 200 have been developed. Multiple prism grating configurations were initially introduced in narrow line width liquid dye lasers, but these were eventually adopted in gas, solid state, and diode laser designs as well. The generalized mathematical description of multiple prism beam expanders introduced by FJ Duarte is known as multiple prism dispersion theory.

Multiple prism beam expanders and arrays can also be described using beam transfer matrices . The multi-prism dispersion theory is also available in 4 × 4 matrix form.

Extra cavity beam shaping

Extra-cavity hybrid beam transformers: With a telescopic beam expander followed by a convex lens and a multi-prism beam expander, a laser beam (with a circular cross-section) can transform in the plane from an extremely elongated beam while it is extremely thin in the orthogonal plane . The resulting plane illumination with an almost one-dimensional (or line) cross-section makes point-by-point scanning superfluous and has become important for applications such as N- slot interferometry , microdensitometry and microscopy . This type of lighting is also referred to in the literature as light sheet lighting or selective area lighting.

Web links

Individual evidence

  1. ^ FJ Duarte: Dye Laser Principles . Ed .: FJ Duarte, LW Hillman. Academic Press , 1990, ISBN 978-0-12-222700-4 , Narrow-linewidth pulsed dye laser oscillators.
  2. ↑ TW Hänsch : Repetitively pulsed tunable dye laser for high resolution spectroscopy . In: Applied Optics . 11, No. 4, 1972, pp. 895-898. bibcode : 1972ApOpt..11..895H . doi : 10.1364 / AO.11.000895 . PMID 20119064 .
  3. ↑ Wolfgang Demtröder: Laser Spectroscopy: Basics and Techniques . Springer, 2007, ISBN 978-3-540-33792-8 .
  4. ^ Wolfgang Demtröder: Laser Spectroscopy Volume 1: Basic Principles . 4th edition. Springer, 2008, ISBN 978-3-540-73415-4 .
  5. ↑ FJ Duarte, TS Taylor, A. Costela, I. Garcia-Moreno, and R. Sastre, Long-pulse narrow-linewidth dispersive solid-state dye laser oscillator, Appl. Opt. 37 : 3987-3989 (1998).
  6. ^ FJ Duarte: Tunable Laser Optics . 2nd Edition. CRC Press , 2015, ISBN 978-1-4822-4529-5 .
  7. ↑ A double-prism beam expander for pulsed dye lasers . In: Optics Communications . 35, 1980, pp. 100-104. bibcode : 1980OptCo..35..100D . doi : 10.1016 / 0030-4018 (80) 90368-5 .
  8. ↑ Dispersion theory of multiple-prism beam expanders for pulsed dye lasers . In: Optics Communications . 43, No. 5, 1982, pp. 303-307. bibcode : 1982OptCo..43..303D . doi : 10.1016 / 0030-4018 (82) 90216-4 .
  9. ↑ Ray transfer matrix analysis of multiple-prism dye laser oscillators . In: Optics and Quantum Electronics . 21, 1989, pp. 47-54. doi : 10.1007 / BF02199466 .
  10. ^ FJ Duarte: High Power Dye Lasers . 1991, ISBN 978-0-387-54066-5 , Chapter 2.