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Definition: the phenomenon that an input laser beam generates a beam with three times the optical frequency
Frequency tripling is a process of nonlinear frequency conversion where the resulting optical frequency is three times that of the input laser beam. In principle, this can be achieved with a χ(3) nonlinearity for direct third-harmonic generation, but this is difficult due to the small χ(3) nonlinearity of optical media and phase-matching constraints (except for tripling in gases). Therefore, frequency tripling is usually realized as a cascaded process, beginning with frequency doubling of the input beam and subsequent sum frequency generation of both waves, with both processes being based on nonlinear crystal materials with a χ(2) nonlinearity.
Figure 1: A typical configuration for frequency tripling: an infrared input beam at 1064 nm generates a green 532-nm wave, and these two mix in a second crystal to obtain 355-nm light.
The main application of frequency tripling is the generation of ultraviolet light. Most common is the generation of 355-nm light by frequency tripling of a laser beam with 1064 nm, as obtained from a Nd:YAG or Nd:YVO4 laser. A common approach is to use two LBO crystals, the first being phase-matched for second-harmonic generation and the second for sum frequency generation. It is easy to make this process efficient when using pulses from a Q-switched or mode-locked laser, but also possible in continuous-wave operation e.g. with intracavity frequency doubling and resonant sum frequency generation.
It is also possible to generate blue light by frequency tripling the output of a 1.3-μm neodymium laser.
See also: frequency doubling, frequency quadrupling, nonlinear frequency conversion, nonlinear crystal materials, ultraviolet light, ultraviolet lasers
Bibliography
| [1] | G. H. C. New and J. F. Ward, "Optical third-harmonic generation in gases", Phys. Rev. Lett. 19 (10), 556 (1967) |
| [2] | W. Seka et al., "Demonstration of high efficiency third harmonic conversion of high power Nd:glass laser radiation", Opt. Commun. 34, 469 (1980) |
| [3] | R. Craxton, "High efficiency frequency tripling schemes for high-power Nd:Glass lasers", IEEE J. Quantum Electron. 17 (9), 1771 (1981) |
| [4] | A. Lago et al., "Coherent 70.9-nm radiation generated in neon by frequency tripling the fifth harmonic of a Nd:YAG laser", Opt. Lett. 13 (3), 221 (1988) |
| [5] | R. Friedberg et al., "Optimizing third harmonic generation in gases", J. Phys. B: At. Mol. Opt. Phys. 24, 2883 (1991) |
| [6] | R. Wu, "High-efficiency and compact blue source: intracavity frequency tripling by using LBO and BBO without the influence of birefringence", Appl. Opt. 32 (6), 971 (1993) |
| [7] | L. Goldberg et al., "Tunable UV generation at 286 nm by frequency tripling of a high-power mode-locked semiconductor laser", Opt. Lett. 20 (15), 1640 (1995) |
| [8] | D. Eimerl et al., "Multicrystal designs for efficient third-harmonic generation", Opt. Lett. 22 (16), 1208 (1997) |
| [9] | J. Squier et al., "Third harmonic generation microscopy", Opt. Express 3 (9), 315 (1998) |
| [10] | Z. Sun et al., "Generation of 4.3-W coherent blue light by frequency-tripling of a side-pumped Nd:YAG laser in LBO crystals", Opt. Express 12 (26), 6428 (2004) |
