This section is home to Mid-IR Hybrid Lasers, a family of CW and pulsed solid-state bulk lasers operating in 1.64 to 5.2 μm wavelength range. Exploiting the synergy of IPG's proprietary capabilities, the Mid-IR Hybrid lasers are typically pumped by IPG's low-cost, reliable and efficient Er and Tm fiber lasers, and many are built with unique active crystals manufactured by IPG. Mid-IR Hybrid lasers span all modes of operation from CW to fs pulsed, and are complementary to Er, Tm and Yb Raman-shifted CW and pulsed IPG fiber laser families.
plastics cutting, welding, marking, drilling
forming of plastics
curing of coatings
Sensing and Imaging:
LIDAR, Doppler scattering
diagnostic, therapeutic, surgical;
molecular identification and dynamics
2D IR correlated spectroscopy
noninvasive nondestructive measurements
chemical agent and biomolecular sensing/ detection
target illumination and designation
Near IR extends from 0.7 µm to about 1.5-2.0 µm. The definition of the boundary between NIR and Mid IR depends on market/application/detection technology.
Near IR Vibrational Bands
From Metrohm “NIR Spectroscopy” monograph
Mid IR Vibrational Bands
• Quantum and Intraband Cascade Lasers
• Lead Salt and GaSb Lasers
• Gas Lasers (CO2,CO, HeNe, frequency doubled CO2)
• Chemical Lasers (HF, DF)
• OPO/ OPA/ OPG
• Free Electron Lasers
• Bulk Solid State such as Er:YAG, Ho:YAG, Ho:YLF and other
• Fiber Lasers (Thulium, Holmium and Erbium doped)
• Many Mid-IR lasers don’t work at room temperature due to deactivation of energy accumulated in gain medium via non-radiative phonon assisted decay.
• Although existing Mid-IR sources already have found use in many applications, they have one or more disadvantages: limited power output, limited wavelength selection, limited range of tunability, low wall plug efficiency, large footprint, complex design, cooling, and high cost.
• Many emerging materials processing, medical, environmental, scientific, etc. applications would be enabled by affordable average and peak power, high pulse energies, room temperature operation, efficient, robust commercial design.
Here come Cr2+ and Fe2+ doped ZnSe/S vibronic solid state lasers.
Vibronic Solid State Lasers
The most important types of vibronic lasers are
• In laser gain media doped with transition metal ions, there is a strong interaction of the electronic states with lattice vibrations, i.e. with phonons.
• This vibrational–electronic (vibronic) interaction leads to a strong homogeneous broadening and thus to a large gain bandwidth.
• Lasers based on vibronic solid-state gain media allow for wavelength tuning over large ranges, and also the generation of ultrashort pulses.
• The first laser demonstrated was a ruby (Cr3+:Al2O3) laser, a vibronic laser.
• Ti:Sapphire lasers 0.68 to 1.08 μm
• Cr3+:LiSAF and Cr3+:LiCAF lasers similar to Ti:S
• alexandrite lasers (Cr3+:BeAl2O3) 0.7 to 0.8 μm
• chromium forsterite lasers (Cr4+:Mg2SiO4) 1.17 to 1.34 μm
• Cr2+:ZnSe/S wide-band semiconductor 1.8 to 3.4 μm
• Fe2+:ZnSe/S wide-band semiconductor 3.4 to 5.2 μm
Cr2+ and Fe2+ Doped II-VI Gain Media
•radiative processes can be sustained at room temperature
•non-radiative decay is suppressed
•ultrabroadband up to 50 % λ,
•room-temperature operation over 1.8-6.1 mm range
Cr/Fe : ZnSe/ZnS/CdSe vibronic lasers: a viable gain and passive Q switch Mid IR media
What is special about TM2+:II-VI?
TM (Cr2+, Co2+, V2+, Mn2+, Fe2+, Ni2+ ) doped II-VI (II-Cd, Zn) (VI- S, Se, Te) compounds have a wide band gap and possess several important features that distinguish them from other oxide and fluoride laser crystals.
Maximum Phonon Frequency, cm-1
•Chemically stable divalent TM dopant ions, no need for charge compensation.
•Crystallization as tetrahedrally coordinated structures, Tetrahedral coordination (Td) gives small crystal field splitting, placing the dopant transitions into the IR.
•Optical phonon cutoff occurs at very low energy, maximizing the prospects for radiative decay of mid-IR luminescence in these crystals.
Why Cr2+ & Fe2+?
•First excited levels lie at the right energy to generate 2-3 (Cr) & 3.5-5 mm (Fe) mid-IR emission.
•The ground and first excited levels have the same spin, and therefore will have a relatively high cross-section of emission.
•Higher lying levels have spins that are lower than the ground and first excited levels, greatly mitigating the potential for significant excited state absorption at the pump or laser transition wavelengths.
•The orbital characteristics of the ground and first excited levels are different, and will experience a significant Franck-Condon shift between absorption and emission, resulting in broadband “dye-like” absorption and emission characteristics, suitable for a broadly tunable laser.
Calculated Multiplet Structure for 3d impurities in ZnSe (after A Fazzio, et al., Phys. Rev. B, 30, 3430 (1984)
Absorption and emission cross-sections of Cr:ZnSe, Cr:ZnS (left) and Fe:ZnSe, Fe:ZnS (right).
S. Mirov, V. Fedorov, D. Martyshkin, I. Moskalev, M. Mirov, S. Vasilyev, “Progress in Mid-IR Lasers Based on Cr and Fe Doped II-VI Chalcogenides”, IEEE Selected Topics in Quantum Electronics (Invited paper), vol. 21, no.1, 1601719 (20pp) (2015).
Spectroscopic characteristics of chromium and iron ions in ZnS, ZnSe at 5T2↔5E transitions, σab, σem,—peak absorption and emission cross-sections; λab, λem—peak absorption and emission cross-section wavelengths, respectively; ΔλFWHM –full bandwidth at half maximum; τrad radiative life time; τRT(τ77K) –luminescence lifetime at room temperature and 77K.
Emission central wavelength, nm
Emission bandwidth, nm
Optical damage threshold, J/cm2
Thermal Conductivity, W/(mK)
Thermooptic coefficient dn/dT, K-1
Absorption central wavelength, µm
Absorption bandwidth, nm
Fluorescence lifetime at 77K (300 K)
•Both gain materials are suitable for direct generation of mid-IR laser radiation within 2-3 µm spectral region
•ZnS host has much better thermal properties
•Cr2+:ZnS suffers from thermal quenching at high internal temperatures
•Cr2+ and Fe2+ ZnSe/S gain media allows broad coverage of Mid IR up to 5.2 microns
•SHG of Cr2+ ZnSe/S extends the coverage into Near IR (from 0.9 microns)
•OPOs extend coverage to longer wavelengths
•Research is under way to expand TM doped ZnSe/S coverage to longer wavelengths
•Cr2+ : ZnSe/S are gain materials of choice when one needs a compact fiber or diode pumped CW (or mode-locked) system with continuous tunability at 300K over 1.8-3.4 µm, output powers up to 20 W, and high (up to 70%) conversion efficiency.
•Fe2+ :ZnSe/S crystals are ideal gain materials for room temperature gain-switched lasers tunable over 3.4-5.2 mm spectral range.
Lasers based on Cr2+, Co2+ and Fe2+ : ZnSe/ZnS crystals are promising for spectroscopic, sensing, medical, and defense related applications, as well as for seeding, or pumping middle-infrared optical parametric oscillators.
High values of saturation cross-section (10-18 cm2)
Small saturation energy (~0.1J/cm2)
Good optomechanical (damage threshold - 2 J/cm2) and physical characteristics of ZnSe and ZnS hosts
Cr2+ and Fe2+: ZnSe/S saturable absorbers are ideal materials for passive Q-switching of mid-infrared laser cavities operating in the spectral range of 1.5-4.0 µm
Diode laser pumping of Mid-IR lasers can be used, provided pump diodes operate in required spectral range. However, diode pumps in this wavelength range have several disadvantages:
The diodes in 1.5-2 μm range have low power
Diodes have low brightness/poor beam mode
Wide spectral bandwidth and poor linewidth control
Er and Tm fiber lasers pumped by 1 μm diodes have wall plug efficiencies as good or better than direct diodes in this wavelength range, and can provide up to 200 W of spectrally pure diffraction-limited output. They provide the high power, high brightness, precise linewidth and linewidth control.
IPG Photonics offers Cr2+, Co2+ and Fe2+ diffusion-doped ZnSe/ZnS polycrystalline ceramic gain materials and saturable absorbers. IPG’s proprietary fabrication process allows low cost mass production of a large variety of iron and chromium doped ZnSe/ZnS crystals with low losses, uniform distribution of transition metal dopant, excellent reproducibility and reliability. The optical and spectroscopic characteristics of these crystals make them the gain materials of choice for compact and efficient laser sources operating in 1.8 to 6 microns range. Chromium and iron doped ZnSe/S lasers are promising for spectroscopy, sensing, medical and defense related applications, as well as for seeding or pumping middle-infrared optical parametric oscillators.
Cr2+:ZnSe and Cr2+:ZnS Laser Active Materials
The unique combination of available pump sources (Er-fiber, Tm fiber, telecom or InP diodes, Er:YAG/YLF; Tm: YAG/YLF), technological (low cost ceramic material), optical and spectroscopic characteristics (ultrbroadband gain bandwidth, high st product and high absorption coefficients) make them the gain materials of choice when one needs a compact system with continuous tunability at 300 K over 1.8-3.4 mm, output powers up to 30 W and high (up to 70%) conversion efficiency.
Cr2+:ZnSe/S lasers are promising for spectroscopy, sensing, medical and defense related applications, as well as for seeding or pumping middle-infrared optical parametric oscillators.
IPG’s fabrication process allows low cost mass production of a large variety of diffusion-doped Cr2+:ZnSe/ZnS crystals with low losses, uniform distribution of chromium, good reproducibility and reliability.
Uniformly-doped 5 x 5 x 20 mm Cr:ZnSe Crystals
Output Characteristics of Cr:ZnSe/S Lasers Based on IPG's Gain Materials
CW Output Power, W
CW Tuning Range, nm
1800 - 3400
CW Efficiency, %
Free-running Energy, J
1.05 @7 ms
Gain-switched Energy, mJ
20 @ 15 ns
Mode-locked Pulse Duration, fs
50 @ 2 W
Fe2+:ZnSe Laser Active Materials
Fe²+:ZnSe crystals are ideal gain materials for room temperature gain-switched lasers tunable over 3.4-5.2 µm spectral range.
These lasers are promising for spectroscopic, sensing, medical and defense related applications, as well as for seeding or pumping middle-infrared optical parametric oscillators.
IPG’s fabrication process allows low cost mass production of a large variety of diffusion-doped Fe²+:ZnSe/ZnS crystals with low losses, uniform distribution of iron, good reproducibility and reliability.
State-of-the-art of Fe:ZnSe Laser Characteristics
CW Output Power, W
Tuning Range, nm
3400 - 5200
Free-running Energy, J
0.42 @ 250 μs @ 5 Hz
Free-running Average Power, W
35 @ 150 μs @ 100 Hz
Gain-switched Energy, mJ
5 @ 15 ns
Please contact IPG Photonics for more information.
Co2+:ZnS, Cr2+:ZnS and Cr2+:ZnSe Passive Q-Switches
Co2+:ZnS, Cr2+:ZnS and Cr2+:ZnSe saturable absorbers (SA) are ideal materials for passive Q-switches of eye-safe fiber and solid-state lasers operating in the spectral range of 1.5-2.1 µm.
These lasers are used in numerous applications such as free-space communication systems, target designation, time-of-flight range finding, surgery, reflectometry and laser lidars.
IPG offers a large variety of diffusion-doped Co2+:ZnS, Co2+:ZnSe, Cr2+:ZnS and Cr2+:ZnSe polycrystals appropriate for Q-switching of the lasers operating in the 1.5-2.1 µm spectral range.
Samples of Cr2+:ZnS, Cr2+:ZnSe and Co2+:Zns Saturable Absorbers
Young Modulus, Pa
Thermal Expansion, deg C-1
Thermal Conductivity, W/(m deg C)
Specific Heat, J/(kg deg C)
Refractive Index at 1.0 µm
dn/dt, deg C-1
Transmission Range, µm
0.37 - 14
0.55 - 20
σGSA (at 1.54 µm)
σESA (at 1.54 µm)
τGSA (at 1.54 µm)
Fe2+:ZnSe, Fe2+:ZnS Passive Q-Switches
Fe2+:ZnSe and Fe2+:ZnS saturable absorbers (SA) are ideal materials for passive Q-switches of solid-state lasers operating in the spectral range of 2.5-4.0 µm.
These lasers (e.g. 3.0 µm Er:YAG/YSGG/YLF are used for pumping middle-infrared Optical Parametric Oscillators and for numerous medical and dental applications.
IPG’s fabrication process allows low cost mass production of a very large variety of diffusion-doped Fe2+:ZnSe/Zns crystals with low losses, uniform distribution of iron, good reproducibility and reliability.
Samples of Fe2+:ZnSe Single and Polycrystalline Saturable Absorbers
Peak Coefficient Absorption, cm-1
Upper Level Lifetime at 300 K, µs
σGSA at 2.8 µm, 10-20 cm2
According to the criterion for saturable absorber Q-Switching
(where sQgsa and AQ are absorption cross section and area of the cavity mode at passive Q-switcher; sYSGG and AYSGG are emission cross section and area of the cavity mode at the gain element) Fe2+:ZnSe/S can be used as a saturable absorber Q-Switch for the Cr:Er:YSGG laser without intracavity focusing.
Output energies of 15 and 85 mJ were achieved in single and multipulse modes of operation, respectively. The combination of a high values of saturation cross-section, small saturation energy with good optomechanical (damage threshold - 2 J/cm2) and physical characteristics of ZnSe and ZnS hosts make Fe2+:ZnSe/S crystals an ideal material for passive Q-Switching of mid-infrared laser cavities.