The term visible lasers is used to denote lasers emitting visible light, or sometimes laser devices generating visible light via nonlinear frequency conversion. Visible light (for human eyes) corresponds to optical wavelengths roughly between 400 nm and 700 nm.
Lasers with Direct Visible Emission
- Various laser diodes can emit visible light. Examples are GaInP and AlGaInP-based red laser diodes, and GaN-based blue-emitting diodes.
- The first demonstrated laser was a ruby laser emitting at 694.3 nm.
- Titanium–sapphire lasers emit mostly in the infrared spectral region, but can be tuned down to roughly 650 nm.
- There are various upconversion lasers, including both bulk and fiber lasers, with visible light emission.
There are also various gas lasers emitting visible light:
- The helium–neon laser was the first gas laser with visible emission. It can emit on various visible wavelengths, including the well-known 632.8 nm red wavelength but also in the green (543.5 nm), yellow (594.1 nm) and orange (604.6, 611.9 nm) spectral region.
- Helium–cadmium lasers (→ metal vapor lasers) emit in the blue at 441.6 nm.
- Argon ion lasers emit mostly at 514.5 and 488 nm, but also at 465.8, 472.7 and 528.7 nm.
- Krypton ion lasers emit at various wavelengths throughout the visible spectrum, in particular at 647.1 nm and 530.9 nm.
- Copper vapor lasers (→ metal vapor lasers) emit at 510.6 nm (green) or 578.2 nm (yellow).
Finally, various dye lasers have broad emission ranges throughout the visible spectral region.
Visible Laser Systems Based on Nonlinear Frequency Conversion
Various methods allow the generation of visible light in laser diodes via nonlinear frequency conversion:
- The most frequently used approach particularly for green and blue emission is frequency doubling, either intracavity or in an external nonlinear crystal (single-pass or resonant). This can be applied to traditional solid-state bulk lasers and also to VECSELs. Most common are green-emitting laser sources based on frequency-doubled 1064-nm neodymium lasers.
- Sum frequency generation in a nonlinear crystal can generate visible light. For example, sum frequency mixing of a 1064-nm Nd:YAG laser and a 1.5-μm fiber laser leads to red light.
- A Raman laser can be pumped with light from a regular laser. This is most often done with solid-state bulk lasers, which may be Q-switched or continuous-wave, and often intracavity frequency doubled.
- For broadband visible radiation, there are laser sources involving supercontinuum generation.
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