Yb:KGW

Yb:KGW
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Yb3+: KGd(WO4)2 (Yb:KGW) is one of the most promising laser active materials. Yb: KGW crystal is expected to replace Nd: YAG crystal and Yb: YAG crystal in high power diode pumped laser system. Yb:KGW also has great potential for high power, short pulse time femtosecond lasers and their wide application.

Yb3+:KGW has large absorption coefficient, low quantum defect, high absorption and emission cross-section

The simple two-level electronic structure of the Yb ion avoids undesired loss processes such as upconversion, excited state absorption, and concentration quenching. Compared to the commonly used Nd: YAG crystal, Yb: KGW crystal has a much larger absorption bandwidth, 3 or 4 times longer emission lifetime in similar hosts with enhanced storage capacity, lower quantum defect, and is more suitable for diode pumping than the traditional Nd-doped systems.

The smaller Stokes shift reduces heating and increases the laser efficiency. In comparison with other Yb-doped laser crystals, such as Yb: YAG and Yb: YCOB crystals, Yb:KGW has the following characteristics:

  • A much higher (13-17 times) cross-section of absorption
  • Lower quantum defect (~4%)
  • A cross-section of emission that is nine times higher than Yb: YCOB
  • An emission band broader than Yb:YAG
  • A high nonlinear coefficient of refraction
  • The width of absorption line is wide, and the pump wavelength of LD pump source with phase matching can be obtained without strict temperature control;
  • The quantum defect is low, and the pump wavelength is very close to the laser output wavelength, which will lead to a large intrinsic laser slope efficiency, and the quantum efficiency is up to about 90% theoretically;
  • Because the pumped energy level is close to the upper laser level, the thermal load in the material without radiation relaxation is low, which is only one third of that of the same laser material doped with neodymium;
  • No excitation state absorption and upconversion, high light conversion efficiency;
  • Long fluorescence life, more than three times that of the same neodymium-doped laser material, is conducive to energy storage;

Physical and Chemical Properties

Chemical FormulaYb3+：KGd（WO4）2
Crystal StructureMonoclinic Double Tungstate
Density7.27 g/cm3
Transmission Range0.35-5.5 μm
Mohs Hardness4 to 5
1060 nm Refractive Indexng = 2.037,
np = 1.986,
nm= 2.033

Optical and Thermal Properties

Thermal ConductivityKa=2.6 W/mK,
Kb=3.8 W/mK,
Kc=3.4 W/mK
Thermo-optic Coefficient@ 1064 nmdnp/dT=-15.7 * 10-6 K-1
dnm/dT=-11.8 * 10-6 K-1
dng/dT=-17.3 * 10-6 K-1
Thermal Expansionαa=4X10-6 /°C
αb=3.6X10-6 /°C
αc=8.5X10-6 /°C
Melting Point Temperature1075 °C
Absorption Cross Section1.2X10-19 cm2
Stimulated Emission Cross Section（E || a）2.6X10-20 cm2
Laser Wavelength1023-1060 nm
Laser Threshold35 mW
Yb3 +的2F5/2Pure energy level of the manifold at 77 K（cm-1）10682, 10471, 10188
The Stark level of the 2F7/2 manifold of Yb3+ in cm-1 at 77K535, 385, 163, 0
Optical damage threshold, GW/cm220

Spectral properties

Absorption Peak Wavelength，lpump，[nm]981.2
Absorption Line Width，Dlpump，[nm]3.7
Peak Absorption Cross Section, Bubbling，[cm2]1.2×10-19
Peak Absorption Coefficient，[cm-1]26
Emission Wavelength，lse，[nm]1023
Emission Line Width，Dlse，[nm]20
Peak Emission Cross Section，sse，[cm2]2.8×10-20
Quantum Effect，lpump / lse，[nm]0.959
Fluorescence Lifetime，tem [ms]0.6

Absorption and Emission Spectra

Yb KGW laser crystals absorption spectroscopy CRYLINK

References

[1]  Major A ,  Cisek R ,  Greenhalgh C , et al. A diode-pumped high power extended cavity femtosecond Yb:KGW laser: From development to applications in nonlinear microscopy[C]// Photonics North 2006. 2006.
[2]  Zhao H ,  Major A . Megawatt peak power level sub-100 fs Yb:KGW oscillators[J]. Optics Express, 2014, 22(25):30425-31.
[3]  Paunescu G ,  Hein J ,  Sauerbrey R . 100-fs diode-pumped Yb:KGW mode-locked laser[J]. Applied Physics B, 2004, 79(5):555-558.
[4]  Kuleshov N V ,  Lagatsky A A ,  Shcherbitsky V G , et al. CW laser performance of Yb and Er,Yb doped tungstates[J]. Applied Physics B, 1997, 64(4):409-413.
[5]  Holtom G R . Mode-locked Yb:KGW laser longitudinally pumped by polarization-coupled diode bars[J]. Optics Letters, 2006, 31(18):2719-21.
[6]  Kuleshov N V ,  Lagatsky A A ,  Podlipensky A V , et al. Pulsed laser operation of Y b-dope d KY(WO(4))(2) and KGd(WO(4))(2).[J]. Optics Letters, 1997, 22(17):1317-9.
[7]  Zhao H ,  Major A . Powerful 67 fs Kerr-lens mode-locked prismless Yb:KGW oscillator[J]. Optics Express, 2013, 21(26):31846-31851.
[8]  Pekarek S ,  Fiebig C ,  Stumpf M C , et al. Diode-pumped gigahertz femtosecond Yb:KGW laser with a peak power of 3.9 kW[J]. Optics Express, 2010, 18(16):16320-16326.
[9]  Hellstroem J E ,  Bjurshagen S ,  Pasiskevicius V , et al. Efficient Yb:KGW lasers end-pumped by high-power diode bars[J]. Applied Physics B, 2006, 83(2):235-239.
[10]  Major A , D Sandkuijl,  Barzda V . Efficient frequency doubling of a femtosecond Yb:KGW laser in a BiB3O6 crystal[J]. Optics Express, 2009, 17(14):12039-42.
[11] S Chénais,  Druon F ,  Balembois F , et al. Thermal lensing measurements in diode-pumped Yb-doped GdCOB, YCOB, YSO, YAG and KGW[J]. Optical Materials, 2003, 22(2):129-137.
[12]  Major A , D Sandkuijl,  Barzda V . A diode-pumped continuous-wave Yb:KGW laser with Ng-axis polarized output[J]. Laser Physics Letters, 2010, 6(11):779-781.
[13]  Hellstrm J E ,  Bjurshagen S ,  Pasiskevicius V . Laser performance and thermal lensing in high-power diode-pumped Yb:KGW with athermal orientation[J]. Applied Physics B, 2006, 83(1):55-59.
[14]  Akbari R ,  Zhao H ,  Fedorova K A , et al. Quantum-Dot Saturable Absorber and Kerr Lens Mode-Locked Yb:KGW Laser with >300 kW of Peak Power[J]. Optics Letters, 2016, 41(16).
[15]  Russbueldt P ,  Mans T ,  Weitenberg J , et al. Compact diode-pumped 1.1 kW Yb:YAG Innoslab femtosecond amplifier[J]. Optics Letters, 2010, 35(24):4169-71.
[16]  Sandkuijl D ,  Cisek R ,  Major A , et al. Differential microscopy for fluorescence-detected nonlinear absorption linear anisotropy based on a staggered two-beam femtosecond Yb:KGW oscillator[J]. Biomedical Optics Express, 2010, 1(3):895-901.
[17]  Hellstrm J ,  Henricsson H ,  Pasiskevicius V , et al. Polarization-tunable Yb:KGW laser based on internal conical refraction[J]. Optics Letters, 2007, 32(19):2783-2785.
[18]  Joel A , Berger,  Michael J , et al. High-power, femtosecond, thermal-lens-shaped Yb:KGW oscillator.[J]. Optics express, 2008.
[19]  Major A ,  Cisek R ,  Barzda V . Development of diode-pumped high average power continuous-wave and ultrashort pulse Yb:KGW lasers for nonlinear microscopy[C]// Commercial and Biomedical Applications of Ultrafast Lasers VI. International Society for Optics and Photonics, 2006.
[20] Alexander, Klenner, Matthias, et al. A gigahertz multimode-diode-pumped Yb:KGW enables a strong frequency comb offset beat signal[J]. Optics Express, 2013.
[21]  Erhard S ,  Gao J ,  Giesen A , et al. High power Yb:KGW and Yb:KYW thin disk laser operation[C]// Conference on Lasers & Electro-optics. IEEE, 2001.
[22]  Zhao H ,  Major A . Orthogonally polarized dual-wavelength Yb:KGW laser induced by thermal lensing[J]. Applied Physics B, 2016, 122(6):1-6.
[23]  Akbari R ,  Zhao H ,  Major A . High-power continuous-wave dual-wavelength operation of a diode-pumped Yb:KGW laser[J]. Optics Letters, 2016, 41(7):1601.
[24] T Balčiūnas, OD Mücke, P Mišeikis, et al. Carrier envelope phase stabilization of a Yb:KGW laser amplifier[J]. Optics Letters, 2011, 36(16):3242.
[25]  Lagatsky A A ,  Abdolvand A ,  Kuleshov N V . Passive Q switching and self-frequency Raman conversion in a diode-pumped Yb:KGd(WO4)2 laser[J]. Optics Letters, 2000, 25(9):616-8.
[26]  Molis G ,  Adomavicius R ,  Krotkus A , et al. Terahertz time-domain spectroscopy system based on femtosecond Yb:KGW laser[J]. Electronics Letters, 2007, 43(3):190-191.
[27]  Hoos F ,  Li S ,  Meyrath T P , et al. Thermal lensing in an end-pumped Yb : KGW slab laser with high power single emitter diodes[J]. Optics Express, 2008, 16(9):6041-6049.
[28]  Kisel V E ,  Rudenkov A S ,  Pavlyuk A A , et al. High-power, efficient, semiconductor saturable absorber mode-locked Yb:KGW bulk laser[J]. Optics Letters, 2015, 40(12):2707-10.

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