ULO Optics use only ‘Lasergrade’ ZnSe material.
ZnSe windows can be fabricated in dimensions from 4.0 to 300mm diameter and thicknesses from 1.0mm up to 50mm (latter depending on material availability). Many standard sizes are manufactured and held in stock. See the parts list below for examples. Square and rectangular ZnSe windows can be fabricated to order.
Unless otherwise specified by the customer or made to special order, the standard tolerances are:
Parallelism: Edge thickness variation (ETV) ≤0.03mm or typically ≤ 2 arcmin
Flatness: Typically λ/40 over any 25mm test diameter at 10.6μm, but the actual specification will depend on thickness.
The limits of accuracy that can be reached at negotiated price are:
Thickness: +/-0.025mm *
Parallelism: < 2arcsec *
Flatness: within λ/200 at 10.6μm.*
* Individually made items only.
High tolerance levels require mechanically rigid substrates of sufficient thickness.
Standard windows are available uncoated or AR/AR coated at 10.6μm. The AR/AR coating functions reasonably well over 9 to 11μm. Other AR coatings are available:
Ultra-low (absorbing) AR/AR at 10.6μm
AR/AR at another wavelength
DBAR/DBAR ‘Dual-Band’ wavelengths, 0.633
and 10.6μm or 1.064 and 10.6μm
BBAR/BBAR ‘Broad-Band’ over 8 to 12μm or 3 to 5μm
WBAR/WBAR ‘Wide-Band’ over 3 to 12μm or 1 to 5μm
Absorption and Laser damage
Typical laser absorption levels at 10.6mm are 0.10 to 0.15% for windows of thickness 3 to 5mm. Ultra-low AR coated windows absorbs about 0.04% less than the standard AR coated window. Component absorption can affect the thermal lensing properties of windows used at high energy densities. Surface contamination can dramatically increase the absorption of a window. Consequently it is important to keep the surfaces clean and in good condition.
CW laser damage thresholds are best expressed in the units of W/mm, i.e. the laser beam power divided by the beam diameter. In these units a standard AR coated ZnSe window has a damage threshold of about 3000W/mm. In other words, a 3kW beam focused down to 1mm diameter or 1.5kW focused to 0.5mm diameter, will damage the window. This value has been verified in lasers up to 5kW. This means that you cannot specify the damage threshold in the more familiar units of W/mm2 without also giving the power as well. Again, surface contamination and also mechanical stress will drastically reduce the laser damage threshold – the damage mechanism is thermally induced stress.
We endeavour to stock the more popular windows both coated AR/AR at 10.6μm and uncoated versions. The table above lists some dimensions, their part numbers and the excess gas pressure they can withstand with a safety factor of x2.