Yb-doped CaGdAlO4 crystal (Yb:CALGO) is now recognized to exhibit outstanding properties for the production of high-power and ultra-short laser pulses. It has the broad and smooth emission bandwidth to generate very short pulses (<100 fs). Additionally its’ high thermal conductivity make it is able to hold high power pumping(2 at. % Yb:CALGO thermal conductivity to be 6.9 and 6.3 WK−1 m−1 along the a and c axis); The generation of both very short pulse and high average power femtosecond oscillators has been demonstrated
Yb3+:CaGdAlO4 has been recently demonstrated to be very interesting for the development of diode–pumped short-pulsed modelocked lasers. Compared with Ti: Sapphire crystal（the choice for the development of ultrashort laser system producing very short and powerful pulses using the Chirped Pulse Amplification technique，Since the beginning of the 90’s）,Yb:CALGO can be directly pumped by very efficient and high power semiconductor laser.( Titanium Sapphire crystal pumped by green laser)
Physical and Chemical Properties
| Formula | Yb:CaGdAlO4 (Yb:CALGO) |
| Crystal Structure | Tetragonal K2NiF4 type structure |
| Melting Point | 1840°C |
| Thermal Conductivity/(W·m-1·K-1) | 11.4(undoped) 6.3(2% Yb:CALGO) 5(5% Yb:CALGO) |
| Thermal Shock Resistance(W.m-1/2) | >4.5 |
| Thermal Expansion /(10-6·K-1 ) | 35 |
Optical and Spectral Properties
| Emission band width* (FWHM) (nm) | 80 |
| Emission Wavelength(nm) | 1018-1052 |
| Minimum theoretical duration (fs) | 14 |
| Central emi ssion peak (nm) | 1050 |
| Absorption (usual pumping) (nm) | 980 |
| Emission cross section(10-20 cm2) | 0.8 |
| Fluorescence lifetime (μs) | 420 |
| σem τ(μscm2) | 336 |
| Quantum Defect | <0.8% |
Main properties of laser materials involved in the development of femtosecond lasers
| Material | Emission band width(FWHM) (nm) | Minimum theoretical duration (fs) | Central emi ssion peak (nm) | Absorption (usual pumping) (nm) |
| Yb:YAG | 9 | 124 | 1031 | 942 |
| Yb:Glass | 35 | 31 | 1020 | 975 |
| Yb:GdCOB | 44 | 26 | 1044 | 976 |
| Yb:BOYS | 60 | 18 | 1025 | 975 |
| Yb:KGW | 25 | 44 | 1023 | 981 |
| Yb:KYW | 24 | 46 | 1025 | 981 |
| Yb:SYS | 73 | 16 | 1040 | 979 |
| Yb:YVO4 | 30 | 36 | 1008 | 984 |
| Yb:CaF2 | 30 | 36 | 1047 | 980 |
| Yb:CALGO | 80 | 14 | 1050 | 980 |
| Material | Emission cross section(10-20 cm2) | Fluorescence lifetime (μs) | σem τ(μscm2) | Thermal conductivity (undoped)(W/m/K) |
| Yb:YAG | 2.1 | 951 | 1997 | 11 |
| Yb:Glass | 0.05 | 1300 | 65 | 0.8 |
| Yb:GdCOB | 0.35 | 2600 | 910 | 2.1 |
| Yb:BOYS | 0.3 | 1100 | 330 | 1.8 |
| Yb:KGW | 2.8 | 600 | 1680 | 3.3 |
| Yb:KYW | 3 | 600 | 1800 | 3.3 |
| Yb:SYS | 0.44 | 820 | 361 | 2 |
| Yb:YVO4 | 1.25 | 250 | 312 | 5.1 |
| Yb:CaF2 | 0.25 | 2400 | 600 | 9.7 |
| Yb:CALGO | 0.8 | 420 | 336 | 11.4 |
Absorption and Emission Spectrum
Material and Specifications
| Doping Concentration | 1-10% |
| Parallelism | 10〞 |
| Perpendicularity | 10ˊ |
| Surface Quality | 20/10 |
| Surface Flatness | <λ/10@632.8nm |
| Clear Aperture | >90% |
| Chamfer | 0.1mm@45° |
| Thickness/Diameter Tolerance | ±0.05 mm |
High thermal conductivity
Large gain bandwidth
Broad and smooth emission bandwidth
Low refractiveindex-temperature gradient
Absorption band is covered by high-power InGaAs laser diodes
Solid state femtosecond oscillators
Ultrafast solid-state laser
time-resolved spectroscopy, multiphoton imaging, micromachining, refractive surgery, acceleration of particles, X-rays generation, fusion, etc.
modelocked laser
BAW device
Diode–pumped short-pulsed modelocked lasers
Femtosecond lasers technology
Bicolor double-pulse regime
Yb:CALGO, it is possible to generate double pulses with different wavelengths, which is to our best knowledge the first demonstration of bicolor femtosecond double-pulse operation. Very broad spectrum has been obtained with a bandwidth greater than 30 nm . The spectrum can be fit with two Gaussians: one centered at 1040 nm with a bandwidth of 21 nm and one centred at 1057 nm with a bandwidth of 10 nm with lower amplitude (60%).