Source: Nature

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Vibronic Lasers: Understanding the Interaction of Electronic States and Phonons

Introduction to Vibronic Lasers

In some laser gain media, particularly those doped with transition metal ions, there is a significant interaction between electronic states and lattice vibrations, known as vibronic interaction. This interaction can lead to laser transitions where not only photons are emitted but also phonons. The vibrational-electronic interaction results in a broadening of the transition, leading to a large gain bandwidth.

Role of Phonons in Rare-Earth-Doped Gain Media

While most rare-earth-doped gain media are not vibronic, phonons still play essential roles in the laser processes of these materials. Phonons facilitate fast thermalization within Stark level manifolds and non-radiative transitions between energy levels, crucial for the pumping mechanism and depopulation of the lower laser level.

Types of Vibronic Lasers

Vibronic solid-state lasers offer wavelength tuning over broad ranges and the generation of ultrashort pulses. Some important types of vibronic lasers include:

• Titanium-sapphire lasers
• Cr3+:LiSAF and Cr3+:LiCAF lasers
• Cr4+:YAG lasers
• Alexandrite lasers
• Chromium forsterite lasers
• Cr2+:ZnSe and Cr2+:ZnS lasers
• Tm3+:YAG lasers

Notable Examples of Vibronic Lasers

The ruby laser, operating at 694.3 nm, is not a vibronic laser as it operates on a narrowband line without phonons. However, most transition-metal-based laser gain media exhibit vibronic interactions.

Advancements in Vibronic Lasers

The first vibronic laser, a Ni:MgF2 laser, was demonstrated in 1963, albeit requiring cryogenic cooling. Fe2+:ZnSe is a relatively new vibronic gain medium that enables mid-infrared emission.

Conclusion

Vibronic lasers, characterized by the interaction of electronic states with phonons, have paved the way for tunable solid-state lasers with broad gain bandwidths and unique emission properties. Understanding the vibronic interactions in laser gain media is crucial for the development of advanced laser technologies.

Source: Researching
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