Overview of Laser Types and Lasing Media

By Owais AliReviewed by Lexie CornerUpdated on Aug 19 2024

Since its first medical application in 1962 to treat skin melanoma, laser technology has significantly expanded and is now employed across numerous medical, manufacturing, and telecommunication technologies. This article provides an overview of various types of lasers and their lasing media, highlighting their applications, advantages, and limitations.¹

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How Lasers Work?

"Laser" stands for light amplification by stimulated emission of radiation. Lasers operate based on the principles of stimulated emission and population inversion.

In a typical laser setup, a pump source excites photons in the gain medium, leading to spontaneous emission. These photons then stimulate excited atoms, causing more photons to be emitted. When the number of excited atoms exceeds those in the ground state (population inversion), stimulated emission dominates, producing coherent laser light.

Properties of Lasers

Lasers have distinct properties that set them apart from conventional light:

• Coherence: Laser light waves are synchronized and maintain a stable wavefront, enabling them to travel long distances with minimal diffraction.
• Mono-chromaticity: The laser consists of a single color or wavelength, determined by the gain medium.
• Collimation: The photons in a laser beam are parallel, preventing divergence and allowing the beam to retain its size and shape over long distances.
• Directionality: Lasers travel in a concentrated, focused beam, providing precise targeting and control essential for applications like cutting.¹

Laser Media and Common Types of Lasers

The laser gain medium (active medium) is a collection of atoms or molecules capable of stimulated emission, which can be in a gaseous, liquid, solid, or plasma state. This medium amplifies light by compensating for resonator losses and dictates the laser's wavelength emissions based on the specific energy level transitions within the material.

Lasers are often named after their gain medium, reflecting the medium's role in generating photons.²

Liquid Lasers

Liquid lasers, commonly represented by dye lasers, use organic dyes dissolved in solvents as their laser medium. These dyes, such as stilbene, coumarin, and rhodamine 6G, absorb light at specific wavelengths and re-emit it at longer wavelengths through fluorescence. The active dye molecules are excited to higher energy states by optical pumping and return to lower energy states by emitting light.

Advantages and Limitations

Liquid lasers offer several advantages, including the flexibility to operate across a broad wavelength range (400-800 nm) due to the customizable nature of the dye solution, which is easy to replace. This capability allows them to target specific wavelengths, such as the 585-595 nm range (yellow visible light), which is effective for cosmetic procedures targeting substances like hemoglobin and melanin.

Additionally, the circulation of the dye solution enables effective heat removal, allowing for variable pulse lengths and radiation power, providing an edge over solid-state lasers.

However, the degradation of organic dyes over time due to photobleaching impacts their longevity and efficiency. They also require high-power pump sources, leading to higher operational costs.^3,4

Semiconductor Lasers

Semiconductor lasers, commonly known as laser diodes, use a semiconductor junction as the laser medium. These lasers operate on the principle of recombination of charge carriers in the junction region, which is typically a thin layer between two-dimensional semiconductor materials.

Unlike other lasers, semiconductor lasers do not require external mirrors for optical feedback; instead, the reflectivity from the junction layers provides sufficient feedback. They can be classified into homojunction and heterojunction types, depending on whether the junction is made from a single semiconductor material or two different materials.

Advantages and Limitations

Semiconductor lasers are compact and easily integrated into portable devices and space-limited applications. They offer high energy conversion efficiency and low power consumption, contributing to significant energy savings. Their ability to operate across a broad range of wavelengths supports diverse applications, while their direct modulation capability makes them ideal for telecommunications and data transmission.

However, they are vulnerable to static electricity discharges and fluctuations in power supply, which can cause damage. Over time, these lasers tend to degrade, leading to reduced effectiveness and increased power usage. Additionally, the laser's lens, used for beam correction, is prone to fragility; any damage to the lens can render the laser inoperable.^3,4

Gas Lasers

Gas lasers generate light by passing an electric current through a gas medium, where accelerated electrons in a discharge tube induce atoms or molecules to achieve population inversion and stimulate emission. The choice of gas, such as helium-neon, argon ion, carbon dioxide, or excimer, determines the wavelength of the emitted light.

These lasers are available across various power levels (milliwatts to megawatts) and wavelengths (UV-IR) and can operate in pulsed or continuous modes.

Advantages and Limitations

Gas lasers provide a wide range of wavelengths, enhancing their versatility for applications needing specific wavelengths. They can achieve high power outputs with excellent beam quality, making them effective for precise and efficient processing. They also exhibit strong coherence and stability, which are crucial for applications demanding high precision and reliability.

However, these lasers are generally larger and more complex, which can restrict their use in space-limited environments. Moreover, gas lasers need periodic refilling and cooling, adding to the operational complexity and maintenance requirements.^3,4

Solid-State Lasers

Solid-state lasers use crystalline or glass substrates such as sapphire, neodymium-doped yttrium aluminum garnet (Nd:YAG), and ytterbium-doped glass as their laser medium. These lasers rely on light energy for pumping, and the doped ions, like neodymium, chromium, erbium, thulium, or ytterbium, provide optical gain.

They can be configured as bulk, fiber, or waveguide lasers, providing output powers ranging from milliwatts to several kilowatts.

Advantages and Limitations

Solid-state lasers deliver high beam quality, providing exceptional precision and focus suitable for diverse applications. They feature efficient energy conversion, minimizing energy waste. Their compact and robust design makes them ideal for industrial and scientific uses, and their long lifespan ensures durability and extended use.

However, solid-state lasers have limited wavelength versatility, which can restrict their use in some applications compared to other laser types. Due to their high power output, they often require cooling systems, adding to the complexity and cost. Furthermore, the initial cost of solid-state lasers is typically higher, which may limit their accessibility for certain applications.^4,5

Applications of Lasers

Solid-state lasers are prominent in industrial and scientific applications, including cutting, welding, LIDAR, and medical procedures like tattoo removal and kidney stone treatment. Nd:YAG lasers are particularly valued in material processing and research, while Neodymium-Doped Glass Lasers are used in high-energy physics and fusion studies.

Gas lasers, including CO₂ and excimer lasers, excel in versatile applications such as material processing, vision correction, and semiconductor manufacturing. They are integral to holography, barcode scanning, and air pollution measurement.

Semiconductor lasers are crucial in modern technology, powering devices like barcode readers, laser pointers, and fiber optic communication systems. They are favored for their efficiency and small size, which makes them suitable for short-distance optical interconnects. These lasers are also used in lithography for nanopatterning, biological imaging, and various industrial and lighting applications.

Despite their historical decline in popularity due to cost and complexity, liquid lasers remain valuable in cosmetology and medical treatments for their unique wavelength capabilities and adjustable power. They continue to be used for vascular surgery and skin treatments, leveraging their precision and effectiveness.^6,7,8

Conclusion

Lasers have become indispensable tools in various industries due to their unique properties and the diverse range of lasing media available. As technology progresses, advancements in laser efficiency, power output, and wavelength range are expected to lead to more compact and versatile laser systems, achieving higher precision, broader application scopes, and enhanced performance across various fields.^1,2

More from AZoOptics: What Role Do Lasers Play in Reducing Plastic Pollution?

References and Further Reading

1. Stenhoff, S., Mills, J. (2023). Basic principles of lasers. Anaesthesia & Intensive Care Medicine. doi.org/10.1016/j.mpaic.2023.10.013
2. Paschotta, R. (2021). Laser Gain Media. RP Photonics Encyclopedia. https://doi.org/10.61835/z5z
3. Singh, SC., Zeng, H., Guo, C., Cai, W. (2012). Lasers: fundamentals, types, and operations. Nanomaterials: Processing and Characterization With Lasers, First Edition, Wiley-VCH Verlag GmbH & Co. KGaA. doi.org/10.1002/9783527646821
4. Han's Laser Corporation. (2023). Advantages, Disadvantages, and Applications of Different Types of Lasers. [Online] Han's Laser Corporation. Available at: https://www.hanslaserus.com/knowledge/advantages-disadvantages-and-applications-of-different-types-of-lasers/
5. Paschotta, R. (2022). Solid-state Lasers. RP Photonics Encyclopedia. https://doi.org/10.61835/qcw
6. Luke, AM., Mathew, S., Altawash, MM., Madan, BM. (2019). Lasers: A review with their applications in oral medicine. Journal of lasers in medical sciences. doi.org/10.15171/jlms.2019.52
7. Pinkerton, AJ. (2016). Lasers in additive manufacturing. Optics & Laser Technology. doi.org/10.1016/j.optlastec.2015.09.025
8. Paschotta, R. (2008). Field guide to lasers. Bellingham, WA: SPIE. doi.org/10.1117/3.767474

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