Ho:YLF

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.

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Parameter

Material and Specifications

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

Physical and Chemical Properties

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%

Optical and Spectral Properties

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