Copper ‘Goldmax’ Mirrors
Goldmax-coated mirrors are the second-most highly reflective of all the Cu mirror types. They
consist of a copper substrate, precision-lapped to the required surface form, plated with a thin layer
of nickel which is polished and then vacuum-coated with a reflectivity enhancing dielectric stack.
The dielectric coating retains high reflectance properties for both ‘S’ and ‘P’ polarizations when used
at 45 degrees incidence angle, with near zero phase shift.
All copper used in the manufacture of these mirrors is high-specification, oxygen-free (OFHC).
The manufacturing methods employed in fabrication of Goldmax mirrors allow a wide range of
mirrors to be offered, including spherically curved types.
Goldmax mirrors can be fabricated in sizes up to 150mm diameter, and in thicknesses to suit the
mirror diameter and type of cooling required.
Metric diameters and thicknesses are treated as standard, and are available from stock or with speedy
Imperial (inch) sizes are usually made-to-order only, and carry a small surcharge.
Long-radius mirrors are available, including: 1, 2, 3, 4, 5, 6, 7.5, 10, 12, 14, 15, 20, 25, 30 metres.
Diameters : +0 / -0.15mm
Thicknesses : ±0.15mm
Parallelism : ETV within 0.05mm
Surface form accuracy : <λ/20 (10.6μm) over 90% of dia.
Surface roughness : <20Å RMS
Phase retardation : <2 degrees (at 45° incidence)
reflectivity : >99.6% (see tables 11.32, 11.33)
LIDT : see below
The reflectivity stated in these specifications is the guaranteed
value. Measured samples usually give slightly higher R% values.
Goldmax mirrors are available with the following custom
* Rectangular or square shapes.
* Custom water-cooling fittings.
* Central or offset holes.
* Holes at 45 degrees to the surface.
* Convex radii.
* Arrays of holes.
Special shapes and sizes, including flanged mirrors, can be made to suit custom requirements in
certain makes of CO2 laser.
Laser Damage Thresholds
A recent series of measurements indicated a typical value of 5.0J/sq cm
for 100 nsec pulses. This translates to a pulsed LIDT value of:
0.50 megawatts/mm2 for 100 nsec pulse length.
Measured values of CW LIDT for uncooled, unstressed Goldmax
mirrors are, typically:
2750 W/mm +/- 10% (section 11.0 explains LIDT units)
The stated LIDT values apply to clean, unstressed components.
Tables 11.32, 11.33 give typical values for the reflectivity of a goldmaxcoated
surface vs. angle-of-incidence (for 10.6μm) and vs. wavelength.
The tables appear slightly to contradict each other.
This is due to the fact that table 11.12 shows computed values for ideal
films of zero absorption, whereas table 11.13 gives the typical
experimentally-measured values of samples.