Raw material properties
Only lasergrade ZnSe is used in the fabrication of lenses. See section M1.0 for detailed optical and mechanical
properties of ZnSe. Dimensions
ZnSe lenses can be fabricated in diameters from 4.0mm up to 250mm, in thicknesses from 1mm to 25mm., and focal
lengths from 3.0mm upwards.
Price List Sections dealing with standard types are:-
4.0 (meniscus and p/’vex); 4.1 and 4.3 (high-gas-pressure types);
4.2 (negative lenses); 4.4 (cylindrical lenses).
For special applications, non-standard sizes can be made to order. Tolerances
Unless otherwise specified by the customer, and made to special order, standard tolerances are:
Diameter : +0/-0.1mm
Centre thickness : ± 0.1mm
Centration : ETV ≤ 0.05mm
Surface form : Spherical within λ/80 at 10.6μm over any 25mm dia test area.
Focal length : Designed and fabricated within 0.5%.
Surface roughness : Within 20Å rms (usually 12Å rms).
Absorption : 0.10% – 0.20% depending on thickness.
Transmission : >99.6% when AR/AR coated for 10.6μm.
Standard lenses are AR/AR coated for 10.6μm. Other AR coatings include:
Laser AR/AR for other wavelengths (eg: 3.39μm, 16μm)
Laser AR/AR for CO lasers (5.0-6.0μm)
Broadband coatings (3-5um or 8-14μm)
Wideband coatings (eg: 3-12μm)
Dual-band coatings (eg: AR/AR for 633nm and 10.6μm)
Standard AR/AR coatings are very-low absorption, which helps to minimize thermal lensing effects when used with
high intensity laser beams. Laser Damage Threshold
CW laser induced damage threshold (LIDT) is best expressed in the form ‘W/mm’. This factor remains constant for
a very wide range of laser powers. The CW LIDT of ULO Optics lenses is 3000W/mm (+/-10%).
This is equivalent to 229kW/cm2 at 5kW laser power (measured result).
Mechanical stresses, and contamination/backspatter all reduce the CW LIDT. Poorly designed mounting arrangements
combined with over-tightening of clamp rings can reduce the LIDT to 100W/mm. Design-Data Service
ULO Optics can supply all relevant information on design parameters to a system designer. For any standard
lens, the information indicated in Fig 4.001 is available on request. This data includes centre thickness and edge thickness
(see ‘Lens thickness’ below).
When the system designer can specify the laser beam
parameters, ULO Opticss can also calculate:
1) Spot size/energy density.
Refurbishment of used lenses
See Technical Data Section 6.00 Thermal lensing
All CO2 laser components exhibit thermal lensing at
sufficiently high beam intensities. Thermal lensing is kept
to a minimum by the use of Lasergrade ZnSe, smooth
polished finish and low absorption coatings. Plano-convex lenses
Plano-convex lenses are generally inferior in performance to the optimum meniscus type for focusing a CO2 laser
beam, although they may be less expensive (in quantity) requiring less raw material to manufacture. Umicore Laser
Optics offer as standard the superior meniscus type, usually made in quantity to reduce unit costs.
Where the plano-convex type is specified by a customer, and the required focal length is such that the specific radiustooling
is unavailable, ULO Optics reserve the right to: either (1) ‘trim’ the nominally flat face with a very
long radius curve so achieving a focal length within tolerance, or, (2) request a part-tooling-charge to enable the specific
convex curve to be produced. Lens thickness
Lenses have two ‘thicknesses’…the centre thickness, ‘CT’ and the edge thickness ‘ET’. Centre thickness is relevant
to the lens design and focal length. Edge thickness is relevant to maximum assist gas pressures, and mounting
Where an enquiry states a thickness, but without other qualification, then this will be taken to refer to the lens centre
thickness. Standard products
The lenses listed below are designed for use at normal processing gas pressures.
These lenses, of standard thickness, include AR/AR coatings for 10.6μm, and are suitable for use over the 9.0-11.0μm
wavelength range. Meniscus lenses are indicated as type ‘M’ and plano-convex lenses as type ‘P/V’.
(4.0B) Most lenses detailed above are available from stock.
(4.0C) ULO Optics will be pleased to quote for plano-convex versions of the meniscus lenses in this
price list. (Except for the listed plano-convex lenses, P/V lenses are made-to-order only).
(4.0D)For lens re-work service, see section 6.00.
(4.0E) For high gas pressure lenses, see section 4.10
(4.0F) For negative lenses, see section 4.20
(4.0G)For mounted lenses, see sections 8.10, 8.20, 8.30.
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