Ho:YLF is a very attractive laser material, because the lifetime of the upper laser level is much longer ( ~ 14 ms) than in Ho:YAG and the emission cross sections are higher. Additionally the thermal lens in Ho:YLF is much weaker, which helps to generate diffraction limited beams even under intense end-pumping.
The primary advantage of directly pumping the Ho 5I7 is that it does not have to depend on energy transfer, which lends itself to various radiative and non-radiative losses. Up-conversion losses that have deleterious effect in high-energy Q-switched lasers are eliminated. In the near future experiments with different Ho:YLF crystals are planned to reduce the laser threshold and increase the maximum output power.
Parameter
Orientation | a-cut |
Clear aperture | >90% |
Face dimensions tolerance | +0/-0,1 mm |
Length tolerance | ±0,1 mm |
Parallelism error | <10 arcsec |
Perpendicularity error | <10 arcmin |
Protective chamfers | <0,1 mm at 45˚ |
Surface quality | 10-5 S-D |
Surface flatness | <λ/10@632,8 nm |
Coatings | R<0,35%@1900-2100 nm on both faces |
LIDT | >10 J/cm2@2060 nm, 10 ns |
Mount | Unmounted |
Crystal structure | tetragonal |
Density | 3.95 g/cm3 |
Mohs hardness | 5 |
Thermal conductivity | 6 Wm-1K-1 |
dn/dT | -4.6×10-6 (||c) K-1, -6.6×10-6 (||a) K-1 |
Thermal expansion coefficient | 10.1×10-6 (||c) K-1, 14.3×10-6 ((||a) K-1 |
Typical doping level | 0.5-1% |
Absorption peak wavelength | 1940 nm |
Absorption cross-section at peak | 1.2×10-20 cm2 |
Absorption bandwidth at peak wavelength | ~18 nm |
Laser wavelength | 2060 nm |
Lifetime of 5I7 energy level | 10 ms |
Emission cross-section | 1.8×10-20 cm2 |
Refractive index @1064 nm | no=1.448, ne=1.470 |
Feature
- Long upper laser level lifetime ~ 15 ms
- Higher emission cross-section
- Naturally birefringent material
- Low dn/dT –> weak thermal lensing
- Highest (to the best of our knowledge) CW output of 21 W for 2-μm Ho:YLF laser
- Efficient Q-switched operation (up to 37 mJ per pulse)
Application
- Remote sensing
- Pollutant Control
- Military defense
Literature
Leave a Reply