Semiconductor lasers are generated via radiative recombination of charge carrier pairs in semiconductors. They are more efficient, cost-effective, and require less power than conventional laser systems, making them a popular choice in the manufacturing, medicine, and energy sectors.
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Semiconductor lasers are based on semiconductor gain media, where generation occurs due to the stimulated emission of photons during inter-band electron transitions under conditions of high carrier concentration in the conduction band.
Most semiconductor lasers have electrically-pumped laser diodes with p-doped and n-doped semiconductor contact, optically pumped semiconductor lasers where the carriers are generated through light absorption, and quantum cascade lasers utilizing intra-band transitions.
The primary components of most semiconductor lasers are elements from the third and fifth groups of the periodic table, such as gallium (Ga), aluminum (Al), indium (In), Phosphorus (P), and Arsenic (As).
The Working Principle of Semiconductor Laser
A semiconductor laser is a semiconductor diode whose active medium is a forward-biased PN junction diode.
A PN junction forms at the interface when a p-type semiconductor with an excess of holes is close to an n-type semiconductor with an excess of electrons.
When a forward bias voltage is applied, electrons and holes from the n-region and p-region, respectively, are pushed into the junction. These holes and electrons attract each other, and when they collide, they emit recombination radiation.
The energy of radiation emitted is equal to the energy band gap of the material, which is the energy differential between the conduction and valence bands.
Why are Semiconductor Lasers Used?
Semiconductor lasers are employed in various applications due to their unique features of small light spot size, monochromatic nature, high light density, straightness and coherence.
In addition, semiconductor lasers use low voltage and constant current modes, resulting in a low power failure rate, safe operation, and minimal maintenance costs.
Industrial Applications of Semiconductor Lasers
Semiconductor lasers are the only efficient light source for fiber optic communication systems. With the rise of fiber optic communication, they have become the focal point of modern communication technology.
2D array surface-emitting semiconductor lasers are ideal light sources for optical parallel processing systems, which will play a significant role in computer and optical neural network technology.
Recent advancements in high-power laser diodes have also made them suitable for material processing applications. In addition, their ability to emit various wavelengths gives them the versatility to be used for high-end scientific applications such as spectroscopy.
Photosensitive chemicals with a strong affinity for tumors are preferentially gathered in malignant tissues and treated with a semiconductor laser by generating reactive oxygen species in tumor tissue without harming healthy tissues.
Another application is optical tweezers, which allow the manipulation of living cells and chromosomes, making them useful for cell synthesis stimulation, cell interaction studies and forensic diagnostics.
Limitations of Semiconductor Lasers
Semiconductors in electronic devices are vulnerable to static electricity discharges, so lasers can cause damage if the power supply is unstable and fluctuating. In addition, semiconductor lasers are subject to gradual aging; they become less effective and use more power.
The laser's lens, which is used for beam correction, can also add to its fragility, and any damage to the lens will render the laser inoperable.
Recent Research and Development
Powerful Single-Mode Semiconductor Laser
The capacity to preserve a single mode of light while maintaining the ability to increase in power and size is now possible thanks to a novel semiconductor laser developed by Berkeley engineers.
In the study published in the journal Nature, the researchers demonstrated that the use of open-Dirac electromagnetic cavities with linear dispersion led to single-mode lasing that could be maintained even as the size of the cavity was increased.
This study implies lasers can be more powerful and span longer ranges for various applications without sacrificing coherence.
High-Power Distributed-Feedback Bragg Semiconductor Laser
In a study published in Applied Sciences, researchers presented a new type of 1550 nm distributed-feedback Bragg semiconductor laser that can be manufactured using a simpler and less expensive process compared to traditional 1550 nm band tunable distributed-feedback Bragg lasers.
The new laser does not require high-precision lithography or secondary epitaxial growth methods and can be produced using i-line lithography, which increases yield and creates stable working conditions.
This makes it a more cost-effective, high-yield, and high-efficiency laser solution for applications in laser ranging, LiDAR and space laser communication.
Continuous-Wave Lasing of Deep-Ultraviolet Semiconductor Laser at Room Temperature
A research group from Nagoya University has achieved a breakthrough in semiconductor lasers. The team conducted the first successful continuous-wave lasing at room-temperature in a deep-ultraviolet semiconductor laser.
This was achieved by reducing crystal defects that previously hindered effective current flow in the laser. By tailoring the side walls of the laser stripe, the researchers could suppress the defects, resulting in efficient current flow and lower operating power.
This study is a significant step towards the development and practical application of semiconductor lasers in various wavelength ranges.
Future Outlooks of Semiconductor Lasers
High-power semiconductor lasers have revolutionized the technology industry with their advancements. These lasers have replaced older technologies and paved the way for new products due to reduced cost and increased efficiency.
The application fields of semiconductor lasers are expanding, and this trend will continue in pursuing cost-effective, higher-power, and shorter-pulse lasers.
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References and Further Reading
Hofmann, M. R., & Koch, S. W. (2022). Semiconductor Lasers. In Springer Handbook of Semiconductor Devices (pp. 851-864). Cham: Springer International Publishing. https://doi.org/10.1007/978-3-030-79827-7_23
Zhang, Z., Kushimoto, M., Yoshikawa, A., Aoto, K., Sasaoka, C., Schowalter, L. J., & Amano, H. (2022). Key temperature-dependent characteristics of AlGaN-based UV-C laser diode and demonstration of room-temperature continuous-wave lasing. Applied Physics Letters, 121(22), 222103. https://doi.org/10.1063/5.0124480
Contractor, R., Noh, W., Redjem, W., Qarony, W., Martin, E., Dhuey, S., ... & Kanté, B. (2022). Scalable single-mode surface-emitting laser via open-Dirac singularities. Nature, 608(7924), 692-698. https://doi.org/10.1038/s41586-022-05021-4
Li, X., Liang, L., Qin, L., Lei, Y., Jia, P., Tang, H., ... & Wang, L. (2022). Development of a High-Power Surface Grating Tunable Distributed-Feedback Bragg Semiconductor Laser Based on Gain-Coupling Effect. Applied Sciences, 12(9), 4498. https://doi.org/10.3390/app12094498