Fibre lasers in the mid-infrared regime are useful for a diverse range of fields, including chemical and biomedical sensing, military applications and materials processing. This Review summarizes the different rare-earth cations and host materials used in mid-infrared fibre laser technology, and discusses the future applications and challenges for the field.

Towards high-power mid-infrared emission from a fibre laser

The New Encyclopaedia Britannica

Infrared (2–12 μm) solid-state laser sources: a review

Frequency down-conversion of solid-state laser sources to the mid-infrared spectral range using non-oxide nonlinear crystals

Quasi-three-level solid-state lasers using trivalent rare earth ions are efficient sources in the near- and mid-infrared spectral regions. Their unique properties arise from special energy level structures in different host materials and highly efficient laser operation became possible with the availability of highly efficient high-brightness pump sources like laser diodes. This work will give an overview of quasi-three-level solid-state lasers emitting in the wavelength range 1–5 μm. Recent research and advances in spectroscopic and laser results will be presented. In comparison to four-level lasers such as e.g. Nd3+ lasers at 1.06 μm, quasi-three-level lasers show a much stronger influence of temperature on laser performance, mainly due to the thermally induced changes in the spectroscopic properties of the laser medium. Nevertheless, highly efficient lasers can be realized by direct diode pumping with high spatial and spectral brightness laser diodes. The population dynamics in the manifolds also play an important role and ion concentrations are used to minimize or maximize energy-transfer effects. These general topics will be addressed in Sect. 1, in which basic aspects of quasi-three-level lasers and their description are discussed. Section 2 deals with the general energy-level structure of trivalent rare earths in hosts, from which the most interesting ions and their transitions can be derived. These ions, Nd3+, Yb3+, Er3+, Tm3+ and Ho3+, are investigated in detail in Sect. 3 in order of their emission wavelengths, focusing on their spectral properties and laser results in different laser architectures and host media. In Sect. 4 the work is finally summarized.

Quasi-three-level solid-state lasers in the near and mid infrared based on trivalent rare earth ions

A simple scheme for generation of high power in the midinfrared is demonstrated. By using a 15 W thulium-doped fiber laser emitting at 1907 nm to pump a Q-switched Ho:YAG laser, we obtained 9.8 W at 2096 nm at a 20 kHz pulse repetition rate with excellent beam quality. The output of this laser was used to pump a doubly resonant zinc germanium phosphide based optical parametric oscillator, and we obtained 5.1 W average power in the 3-5 μm range with M2≈1.8.

Midinfrared laser source with high power and beam quality

Arisholm, Gunnar; Nordseth, Ornulf; Rustad, Gunnar. 
Optical parametric master oscillator and power amplifier for efficient conversion of high-energy pulses with high beam quality. Optics Express 2004 ;Volum 12.(18) s. 4189-4197

Optical parametric master oscillator and power amplifier for efficient conversion of high-energy pulses with high beam quality

A high power, efficient, and tunable laser source in the 8–10 µm range, based on a ZnGeP2 optical parametric oscillator (OPO) pumped by a hybrid 2.1 µm laser is demonstrated. The hybrid laser consists of a Q-switched Ho:YAG laser pumped by a 15 W CW thulium fiber laser. With 8.9 W of 2.1 µm pump power we obtained 0.95 W at 8 µm with an M2- value of 2.7 from an OPO with two walk-off compensating crystals.

High power and efficient long wave IR ZnGeP2 parametric oscillator.

The resonator length of an optical parametric oscillator (OPO) is normally made a short as possible to minimize the signal-buildup time and maximize the output energy. We have found that, when a doubly resonant OPO is pumped by a multilongitudinal-mode beam, its output energy has a significant maximum when its optical length matches that of the pump source, even if this length is much greater than the shortest possible for the OPO. We have observed this effect in a ZnGeP>(2)-based OPO and reproduced it in numerical simulations.

Effect of resonator length on a doubly resonant optical parametric oscillator pumped by a multilongitudinal-mode beam

Absorption at the idler wavelength in an optical parametric oscillator (OPO) is often considered detrimental. We show through simulations that pulsed OPOs with significant idler absorption can perform better than OPOs with low idler absorption both in terms of conversion efficiency and beam quality. The main reason for this is reduced back conversion. We also show how the beam quality depends on the beam width and pump pulse length, and present scaling relations to use the example simulations for other pulsed nanosecond OPOs.

Gunnar Rustad

Papers

Midinfrared laser source with high power and beam quality

Optical parametric master oscillator and power amplifier for efficient conversion of high-energy pulses with high beam quality

High power and efficient long wave IR ZnGeP2 parametric oscillator.

Effect of resonator length on a doubly resonant optical parametric oscillator pumped by a multilongitudinal-mode beam

Effect of idler absorption in pulsed optical parametric oscillators.