Tm:YLF Fluoride Crystal

03 Jul 2020

Description

Tm:YLF is the important middle infrared laser crystal. Because Tm:YLF is negative uniaxial crystal, whose thermal refractive index coefficient is negative, some thermal distortion may be counteracted and high-quality light can be output. Conveniently pumped at 792nm, 1.9μm linearly polarized beam is output in a axis, and non-linearly polarized beam is output in c axis. The YLF crystals has low non-linear refraction index value and thermo optical constants, which makes theses crystals applicable in research, development, education, production, photonics, optic, laser technology and telecommunications.

Tm³⁺:YLF lasers are ideal to be used as pump source for Ho³⁺:YAG lasers.

Yttrium lithium fluoride (YLF) is a particularly attractive choice as the host medium for thulium, when it is used as pump source for a 2.1 μm Ho:YAG laser. This is due to the good overlap of the emission peaks with the absorption spectrum of Ho:YAG. YLF is a naturally birefringent material, capable of producing linearly polarized output with virtually no depolarization loss.

Parameter

Material and Specifications

Concentration Tolerance (atm%)	2-4 at.%
Lattice Constants	4~5
Orientation	a-cut, other orientations also available
Parallelism	<10”
Perpendicularity	<5”
Surface Quality	10^-5 scratch & dig
Wavefront Distortion	λ/8 @ 633nm
Surface Flatness	λ/10 @ 633nm
Clear Aperture	95%
Length Tolerance	±0.1 mm
Face Dimensions Tolerance	+0/-0,1 mm
Protective Chamfers	<0,1 mm at 45˚
Damage Threshold	over 15J/cm2 TEM00, 10ns, 10Hz

Physical and Chemical Properties

Crystal Structure	Tetragonal
Lattice Constants	a=5.16Å; c=10.85Å
Density	3.99 g/cm³
Melting Point	819℃
Thermal Conductivity	6 Wm^-1K^-1
Thermal Optical Coefficient(d_n/d_T)	π = 4.3 x 10^-6 x °K^-1; σ = 2.0 x 10^-6 x °K^-1
Thermal Expansion /（10^-6·K^-1@25°C ）	10.1×10-6 (//c) K-1, 14.3×10-6((//a) K-1
Hardness (Mohs)	5
Shear Modulus /Gpa	85
Specific Heat	0.79 J/gK
Poisson Ratio	0.3

Optical and Spectral Properties

Laser Transition	³F₄→³H₆
Laser Wavelength	π:1880 nm; σ:1908 nm
Absorption Cross-section at Peak	0.55×10^-20 cm²
Absorption Bandwidth at Peak Wavelength	16 nm
Absorption Peak Wavelength	792 nm
Lifetime of ³F₄ Thulium Energy Level	16 ms
Quantum Efficiency	2
Non-linear Index n₂	0.6 x 10^-13
Optical Quality	< 0.3 x 10-5
Refractive Index @1064 nm	n_o=1.448, n_e=1.470
Laser Induced Damage Threshold	>10 J/cm²@1900 nm, 10 ns
Coatings	R<0,5% @792 nm + R<0,15% @1800-1960 nm on both sides; custom coatings also available