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Section 3:
Common Laser Types
Lasers are often classifi ed by the gain medium used for light amplifi cation.
Common gain media types are gas, semiconductor (diode), and solid
state. The key parameters of laser systems can be found on pages 6-7.
Section 3.1: Overview of
Common Industrial Lasers
Figure 3.1 shows 23 of the most common lasers and their wavelengths,
modes of operation, and typical gain media.
Gas lasers, such as helium neon (HeNe), are often used for metrology
applications due to their high beam quality and long coherence length.
Other types of gas lasers, such as carbon dioxide (CO2) lasers, are frequently
used for materials processing because they can reach exceptionally
high average powers.
Diode lasers contain a semiconductor p-n junction as the gain medium.
They tend to have the highest power-to-cost ratio and benefi t from high
power conversion effi ciency, high quantum effi ciency, and a wide range
of available wavelengths. Diode lasers are utilized in many applications
including telecommunication, materials processing, bar code scanning,
medical lasers, and LIDAR systems.
Solid state lasers utilize crystals or glass materials doped with transition
metal or rare earth ions. They are often utilized for high power
applications, such as material processing and medical lasers, because
they can reach some of the highest peak powers out of all commercially
available lasers,3 However, it is harder to cool solid state gain media,
which limits repetition rate and average power.
Two special cases of solid state lasers are quantum cascade lasers
(QCLs) and interband cascade lasers (ICLs). QCLs are tunable, semiconductor,
mid-IR lasers that operate through intersubband transitions in
alternating layers of thin semiconductor layers, or “wells”. Intersubband
transitions are excitations between quantized energy states within the
conduction band (Figure 3.2). Because of the extremely small size of the
wells, quantum eff ects take over and the emission wavelength shifts as a
function of well thickness. QCLs can produce high power at long wavelengths
through the combination of both quantum and cascade eff ects.
Most commercially-available QCLs tend to have wavelengths around
4 -11 μm, but the extremes of commercially available QCLs have wavelengths
ranging from 2,63 - 150 μm,4.5,6
ICLs are similar to QCLs in that they use layered semiconductor structures
and quantum wells for mid-IR lasing, but photons are generated
through interband rather than intrasubband transitions (Figure 3.2). They
are able to operate with lower input powers than QCLs.
Fiber lasers are a special type of solid state laser which use an optical
fi ber doped with rare earth ions as the gain medium. They are optimal
for creating very fi ne features in highly precise machining and medical
applications because they contain a high average power in a single optical
mode with high beam quality.
Thin-disk lasers are another special type of solid state laser in which
the gain medium is a very thin disk of solid material. They are a balance
between fi ber lasers and other solid state lasers in that they achieve a
high peak power and gain while utilizing a geometry that makes them
easier to cool, improving their repetition rate and average power. However,
they require complex system designs and therefore cost more than
other laser types.
Figure 3.1: Common commercial lasers with typical modes of operation
and gain media, where CW stands for continuous wave1,2
Conduction Band
ESB
v = h/Eg
(a) Valance Band (b)
Eg
v = h/ESB
Figure 3.2: Comparison of (a) interband and (b) intersubband transitions
in a cascade laser
References
1. Paschotta, Rüdiger. Encyclopedia of Laser Physics and Technology,
RP Photonics, October 2017, www.rp-photonics.com/encyclopedia.html.
2. Lasers and Their Uses Reference Wall Chart. Photonics Media, 2010
3. Weber, Marvin J. Handbook of laser wavelengths. CRC Press, 1999.
ISBN 978-0-8495-3508-2.
4. Cathabard, O., Teissier, R., Devenson, J., Moreno, J.C. and
Baranov, A.N., 2010. Quantum cascade lasers emitting near 2,6 μ m.
Applied Physics Letters, 96(14), p,141110.
5. Walther, C., Fischer, M., Scalari, G., Terazzi, R., Hoyler, N. and
Faist, J., 2007. Quantum cascade lasers operating from 1,2 to 1,6 THz.
Applied Physics Letters, 91(13), p,131122.
6. Wade, A., Fedorov, G., Smirnov, D., Kumar, S., Williams, B.S., Hu, Q. and
Reno, J.L., 2009. Magnetic-fi eld-assisted terahertz quantum cascade laser
operating up to 225 K. Nature Photonics, 3(1), pp,41-45.