vibronic lasers (original) (raw)
Definition: lasers based on gain media with a large gain bandwidth, caused by a strong interaction of electronic transitions with phonons
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optical materials, 
laser devices and laser physics
Related: transition-metal-doped laser gain mediachromium-doped laser gain mediatitanium–sapphire lasersphononsgain bandwidthgas lasersmid-infrared laser sources
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Contents
What are Vibronic Lasers?
Vibronic lasers are tunable solid-state lasers (and some molecular lasers) in which the lasing transition involves both an electronic transition and the creation or annihilation of one or more phonons (quanta of lattice vibrations). Strong electron–phonon (vibronic) coupling produces unusually broad emission and absorption bands, since phonons are available with a wide range of frequencies. This enables wide wavelength tuning and the generation of ultrashort pulses.
Early literature called these systems phonon-terminated lasers. The first demonstration was a Ni:MgF2 laser at Bell Labs in 1963 [1], which required cryogenic cooling. McCumber provided a foundational theory the following year {McCumber 1964}.
Rare-earth-doped Media
Rare-earth-doped laser gain media are mostly not vibronic, since the 4f shell is shielded by outer 5s/5p electrons, which leads to weaker coupling with phonons. Nevertheless, phonons can play important roles in their laser processes. In particular, they lead to the fast thermalization within Stark level manifolds and to fast non-radiative transitions between manifolds with a not too large energy spacing. In many cases, such fast non-radiative transitions are essential for the mechanism of pumping and/or for depopulating the lower laser level.
Exceptions are rare-earth-doped media where 5d–4f transitions are utilized, e.g. in Ce3+, Pr3+, Tb3+ or Eu2+). As the 5d orbital is not shielded, the coupling to phonons is much stronger.
Types of Vibronic Lasers
Solid-state Lasers
Vibronic solid-state lasers are all based on transition-metal-doped laser gain media, containing ions such as Ti3+, Cr3+, Cr4+, Ni2+ and Fe2+. The 3d-electrons interact strongly with the host lattice, giving broad vibronic bands and large gain bandwidths.
The most important types of vibronic solid-state lasers are:
- titanium–sapphire lasers for wavelengths between 0.65 and 1.1 μm, also allowing the shortest pulse duration with passive mode locking
- Cr2+:ZnSe and Cr2+:ZnS lasers for very broad emission in the mid-infrared region at 2.1–3 μm [10] or even up to 3.5 μm
- Cr3+:LiSAF and Cr3+:LiCAF lasers (colquiriite lasers) [8], rivaling Ti:sapphire lasers, with a potential for diode pumping, although with a lower gain bandwidth
- alexandrite lasers (Cr3+:BeAl2O3) for 0.7–0.82 μm, an early type of tunable solid-state lasers
- Cr4+:YAG lasers, emitting around 1.35–1.65 μm
- chromium forsterite lasers (Cr4+:Mg2SiO4) for 1.17–1.34 μm, a wavelength region difficult to access with other lasers
- Fe2+:ZnSe, a newer mid-IR system for ≈3.7–5.3 μm [13]
Note that not all transition-metal-based gain media are vibronic. For example, the ruby laser operating at 694.3 nm is not a vibronic laser; it is operating on the (phonon-less) narrowband R1 line. Some solid-state laser gain media such as alexandrite exhibit both vibronic and non-vibronic (“R line”) transitions; the latter have much lower optical bandwidths.
Molecular Lasers
The term vibronic lasers is also used in the context of molecular gas lasers if lasing occurs between vibrational levels of different electronic states:
- excimer lasers emitting in the ultraviolet — for example ArF at 193 nm, KrF at 248 nm and XeCl at 308 nm
- CO lasers at 500–650 nm
- (Note: the far more common CO lasers operate in the mid-infrared on vibrational-rotational transitions and are not vibronic.)
- nitrogen (N2) lasers for 337 nm
- NO lasers at 1.8–5 μm
- O2 lasers at 762 nm
Not all molecular lasers are vibronic — for example, CO2 lasers.
Frequently Asked Questions
This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).
What is a vibronic laser?
A vibronic laser is a type of laser where the lasing transition involves a change in both the electronic state of the active medium and its vibrational state, involving the creation or annihilation of phonons.
What is the key advantage of vibronic lasers?
What kind of gain media are used for solid-state vibronic lasers?
Why are most rare-earth-doped lasers not vibronic?
In rare-earth-doped laser gain media, the active 4f electrons are shielded by outer electron shells. This results in weak coupling to lattice vibrations (phonons), leading to narrow emission lines rather than broad vibronic bands.
Are all lasers with transition-metal ions vibronic?
No. A prominent example is the ruby laser (Cr3+ in sapphire), which operates on a narrow, non-vibronic (phonon-less) R-line transition. Some media, like alexandrite, can exhibit both vibronic and non-vibronic transitions.
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Bibliography
| [1] | L. F. Johnson, R. E. Dietz and H. J. Guggenheim, “Optical maser oscillations from Ni2+ in MgF2 involving simultaneous emission of phonons”, Phys. Rev. Lett. 11 (7), 318 (1963); doi:10.1103/PhysRevLett.11.318 |
|---|---|
| [2] | D. E. McCumber, “Theory of phonon terminated optical masers”, Phys. Rev. 134 (2A), A299 (1964); doi:10.1103/PhysRev.134.A299 |
| [3] | C. F. Cline et al., “Physical properties of BeAl2O4 single crystals”, J. Materials Sci. 14, 941 (1979); doi:10.1007/BF00550725 |
| [4] | J. C. Walling et al., “Tunable alexandrite lasers”, IEEE J. Quantum Electron.16 (2), 1302 (1980); doi:10.1109/JQE.1980.1070430 |
| [5] | A Budgor, “Overview of chromium doped tunable vibronic lasers”, Proc. SPIE 0461, New Lasers for Analytical & Industrial Chemistry, 62 (1984); doi:10.1117/12.941074 |
| [6] | J. Walling et al., “Tunable alexandrite lasers: Development and performance”, IEEE J. Quantum Electron. 21 (10), 1568 (1985); doi:10.1109/JQE.1985.1072544 |
| [7] | P. Schwendimann, “Model for laser action in vibronic systems”, Phys. Rev. A 37 (8), 3018 (1988); doi:10.1103/PhysRevA.37.3018 |
| [8] | S. A. Payne et al., “LiCaAlF6:Cr3+: a promising new solid-state laser material”, IEEE J. Quantum Electron. 24 (11), 2243 (1988); doi:10.1109/3.8567 |
| [9] | Cr. R. Pollock et al., “Cr4+ lasers: present performance and prospects for new host lattices”, IEEE Sel. Top. Quantum Electron. 1 (1), 62 (1995); doi:10.1109/2944.468370 |
| [10] | I. T. Sorokina et al., “Efficient broadly tunable continuous-wave Cr2+ :ZnSe laser”, J. Opt. Soc. Am. B 18 (7), 926 (2001); doi:10.1364/josab.18.000926 |
| [11] | E. Sorokin et al., “Ultrabroadband infrared solid-state lasers”, JSTQE 11 (3), 690 (2005) (a review mainly concerning Cr2+ and Cr4+ lasers) |
| [12] | A. Teppitaksak et al., “High efficiency >26 W diode end-pumped Alexandrite laser”, Opt. Express 22 (13), 16386 (2014); doi:10.1364/OE.22.016386 |
| [13] | P. Fjodorow et al., “Room-temperature Fe:ZnSe laser tunable in the spectral range of 3.7–5.3 µm applied for intracavity absorption spectroscopy of CO2 isotopes, CO and N2O”, Opt. Expr. 29 (8), 12033 (2021); doi:10.1364/oe.422926 |
| [14] | Y. Cheng et al., “Phonon engineering in Yb:La2CaB10O19 crystal for extended lasing beyond the fluorescence spectrum”, Light: Science & Applications 12 (1) (2023); doi:10.1038/s41377-023-01243-x |
| [15] | I. T. Sorokina, “Crystalline mid-infrared lasers” (eds. I. Sorokina and K. L. Vodopyanov), in Solid-State Midinfrared Laser Sources, Springer, Berlin (2004) |
(Suggest additional literature!)
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