Ruby Lasers

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Definition: solid-state lasers based on a ruby crystal

Category: article belongs to category laser devices and laser physics laser devices and laser physics

DOI: 10.61835/kxz Cite the article: BibTex plain text HTML Link to this page LinkedIn

A ruby laser is a red solid-state laser based on a synthetic ruby laser crystal as gain medium. Ruby is chromium-doped corundum (aluminum oxide, Cr³⁺:Al₂O₃). The first laser, demonstrated by Theodore H. Maiman at Hughes Research Laboratories in 1960, was a free-running flash-lamp pumped ruby laser emitting at 694.3 nm [1]. Optical pumping is possible in the green and blue spectral region.

Although many other solid-state lasers have later on been developed, ruby lasers belong to the relatively few solid-state visible lasers; most others are emitting in the infrared spectral region. In contrast to other red lasers, such as helium–neon lasers, they are suitable for generating intense pulses.

Ruby belongs to the class of three-level laser gain media and therefore requires quite high pump intensities for producing laser gain. Nd:YAG, a prominent example for a four-level gain medium, is much easier to operate. In addition, the required green or blue pump light makes diode pumping similarly difficult as for titanium–sapphire lasers; it is possible, however, with blue laser diodes [2]. Mostly, ruby lasers are pumped with flash lamps, either in free-running mode (with pulse durations of the order of 1 ms) or with Q switching for nanosecond pulse with correspondingly higher peak power. Quite high pulse energies (e.g. 1 J) can be achieved, although hardly in combination with high beam quality.

Due to their limited performance, ruby lasers are not widely used. Initial applications were for laser rangefinders, high-speed photography, pulsed holography, tattoo and hair removal (→ medical lasers), apart from the pulsed pumping of infrared dye lasers. Nowadays, some Q-switched ruby lasers are used for diamond drilling.

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Encyclopedia articles:

Bibliography

[1]	T. H. Maiman, “Stimulated optical radiation in ruby”, Nature 187, 493 (1960) (first experimental demonstration of a laser); https://doi.org/10.1038/187493a0
[2]	W. Luhs and B. Wellegehausen, “Diode pumped cw ruby laser”, OSA Continuum 2 (1), 184 (2019); https://doi.org/10.1364/OSAC.2.000184

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Questions and Comments from Users

2023-09-06

Can a ruby laser really produce single mode beam (transverse and longitudinal)?

Also, a ruby laser operates on two separate wavelengths (R1 and R2), so how can one force it to operate in R1 and suppress R2?

The author's answer:

In such respects, a ruby laser is not different from other solid-state lasers. With lamp pumping, as in the original experiments, it may be difficult, though, to get it single-mode.

You can insert some optical filter to suppress lasing on one of the lines.

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