The water absorption spectrum has a huge peak around 3 um and this is great for many reasons. First, it is possible to build lasers operating near this region. Second, we, as a human being consisting of more than 70% of water, are good candidates to try such lasers on us. Let me explain what I mean. The below figure is the absorption graph of the water up to 10 micron. The absorption peak around 2.9 um is 100 times higher than absorption at 10.6 um and 1000 times higher at 1.06 um (this is a classical wavelength of and 2.1 um this is wavelength of Thulium lasers. Namely, if we have lasers operating near 2.9 um, we will be able to process the materials consisting of water much efficiently than other laser wavelength.

Today, there are three popular technologies that we could use to generate laser wavelength near 3 um. The most known is the Er:YAG solid state lasers. This technology is mature and has very good advantages such as generating high pulse energy (multi-mJ-level) and output power (above 50W) is possible. On the other hand, the pulse duration capability of such systems is limited to microsecond or dozens of nanosecond length. Additionally, the beam quality at high power levels is low. Another laser type is optical parametric generators, which are very promising systems especially for generating short pulses near 3 um. Differently from Er:YAG systems, it is possible to obtain high output power and single mode beam quality at the same time. However, improving pulse energy or output power leads to foot print of such systems larger and larger, and they are getting more complex and expensive. Lastly, fluoride fiber lasers are newer technology compared to two others and provides many advantages and also some disadvantages. First of all, they are simple and versatile, the beam quality obtained from such systems is quite good and it is possible to achieve high-power levels. However, in pulsed mode, they have low damage threshold, either laser induced damage or thermal damage, due to low glass transition temperature. Moreover, lack of fluoride components such as WDMs, fiber coupled isolators etc. is a problem and it limits the architectures and performance of the fluoride fiber-based laser systems.
Achiving higher output levels is important for the most of the materials processing applications. Because of such pros and cons explained above, one of the method is to combine both solid state and fiber technology in order to achieve high pulse energy and output power.