Source: Nature

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Understanding Upconversion Lasers

Introduction

Upconversion lasers are a type of laser where the emitted photon energy is higher than that of the pump source, resulting in a shorter wavelength. This phenomenon is achieved through upconversion pumping schemes, where multiple pump photons are used to transfer a laser ion to a highly excited level.

Types of Upconversion Lasers

Upconversion lasers can be categorized based on the materials used for their construction. Early upconversion lasers utilized bulk crystals that required cooling to very low temperatures. However, advancements have led to the development of upconversion lasers based on glass fibers, which allow for high pump intensities over long lengths.

Examples of Upconversion Fiber Lasers

• Thulium-doped blue upconversion lasers: These lasers are pumped around 1120–1140 nm and emit light around 480 nm.
• Erbium-doped green upconversion lasers: These lasers are pumped around 980 nm and emit light around 546 nm.
• Praseodymium/ytterbium-doped upconversion lasers: These lasers are pumped around 850 nm and emit light in various visible wavelengths in the red, orange, green, or blue spectral regions.

Advantages and Challenges

Upconversion lasers offer the advantage of generating shorter laser wavelengths, which can be beneficial for various applications. However, the choice of materials is crucial, with heavy-metal fluoride glasses often being preferred over silica glass due to their ability to maintain longer metastable level lifetimes.

Future Developments

Research in the field of upconversion lasers continues to focus on improving efficiency, expanding the range of achievable wavelengths, and reducing costs associated with materials and manufacturing processes. Nonlinear frequency conversion methods are also being explored as alternative approaches to obtaining shorter laser wavelengths.

Conclusion

Upconversion lasers represent a unique class of lasers that offer the potential for generating shorter wavelengths than traditional laser systems. With ongoing research and development efforts, the capabilities and applications of upconversion lasers are expected to expand in the future.

Source: Wikipedia
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