Tunable Coherent Light Sources in the Visible and UV Spectrum

Abstract of PhD-thesis

The title of this project is "Tunable Coherent Light Sources in the Visible and UV Spectrum". In this project a new approach to generate tunable ultra violet (UV) and yellow light is investigated. Light in these spectral areas is useful in many applications within research, biology, medicine and entertainment. The approach is based on sum frequency mixing of a tunable laser and its pump source. The technique was implemented on a system based on the Ti³⁺:sapphire laser and on a system based on the Cr⁴⁺:forsterite laser.

First a intracavity frequency doubled Ti³⁺:sapphire laser was constructed. In this setup the nonlinear crystal BiB₃O₆ was used. The laser yielded 100 mW at 405 nm, as well as 53 mW at 393 nm. It was demonstrated that the system could be tuned 7 nm around the latter wavelength. By placing a BiB₃O₆ crystal intracavity in a Ti³⁺:sapphire laser and pumping this laser through the BiB₃O₆ crystal, 5 mW at 319 nm and 3.4 mW at 317 nm was generated by sum frequency mixing. However this system was not continually tunable.

An experiment was conducted in which a beam from a Cr⁴⁺:forsterite laser was single passed through a periodically poled lithium niobate crystal, placed intracavity in a Nd:YVO⁴ laser. This experiment yielded tunable yellow light from 573 to 587 nm. In another system the nonlinear crystal was placed intracavity in a Cr⁴⁺:forsterite laser. The Nd:YVO4 based pump beam was first passed through this nonlinear crystal, before it was absorbed by the Cr⁴⁺:forsterite laser, whereby tunable light from 572 to 579 nm was generated.

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Selected results

A number of different tuneable Ti:Sapphire laser has been build. Both lasers where the tuning element is a prism and where it is a birefringent filter has been constructed and both in linear and ring cavity versions. A typical tuning curve can be seen in Figure 1.

A first attempt to make UV by sum frequency generation failed and the nonlinear crystal (BiBO) was unfortunately damaged. Therefore a new setup making second harmonic generation was made instead, with this setup blue light at 392.5 nm was produced, the result can be seen in Figure 2.

Note that this curve only represents a first “quick and dirty” experiment, in later experiments several mW was archived. A new nonlinear crystal for Sum frequency generation has been ordered, and it is expected to have the first results with UV generation shortly after this crystal has arrived. Whit respect to the generation of yellow light there are still problems getting the Cr:Forsterite laser to oscillate, to change this situation a new Cr:Forsterite crystal with lower doping, and a more sensitive power meter has been ordered. A Nd:YVO laser has been constructed to pump the Cr:Forsterite laser, this laser can produce more than 6 W CW at 1064nm. In a parallel project a Yellow-orange laser has been build by which can give more than 600 mW of light.

References

1. J. Janousek,  S. Johansson,  P. Tidemand-Lichtenberg,  S. Wang,  J. L. Mortensen,  P. Buchhave, and F. Laurell, "Efficient all solid-state continuous-wave yellow-orange light source," Opt. Express 13, 1188-1192 (2005),
   http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-4-1188

Figure 1: Tuning curve of the Ti:Sapphire

Figure 2:  Blue output as a function of the pump power

Figure 3: Phase match diagram showing the phase-mismatch as a function of the cutting angles