Re: Laser Mirror

in article [EMAIL PROTECTED], AES/newspost at
[EMAIL PROTECTED] wrote on 11/27/03 8:58 AM:

> In article <[EMAIL PROTECTED]>,
> "mhr_54" <[EMAIL PROTECTED]> wrote:
> 
>> Does anybody have a 33% reflectivity Ruby wavelength (694nm) laser mirror?
> 
> Haven't put numbers into the etalon peak reflectivity vs refractive
> index calculation to check, but the peak reflectivity from a thick
> glass, quartz, sapphire, or ??? etalon might provide a low-cost (and low
> loss, high damage threshold) solution.

As a rough calculation, the reflectivity of a glass-to-air interface is
0.04. Thus the reflection coefficient is O.2. Adding (an approximation only)
contributions from from front and back surfaces give a reflection
coefficient of 0.4 or a reflectivity of 16%.

Another way of looking at it is to assume that the etalon works as a laser
output coupler at the frequency that gives greatest reflectivity. That means
that it is effectively a quarter-wave thick or an odd multiple of that. To
get 33% reflectivity requires a reflection coefficient of 0.574. To get this
at a single surface requires n=3.70. Considering the etalon to be a
quarter-wave transformer, it has to be made from a material of index
sqrt(3.70) = 1.924. That is pretty tough, but probably not impossible, to do
with readily available glass.

Bill