From: luweitest@address.invalid
On 2015-10-15 4:19, Samuel M. Goldwasser wrote:
> Lu Wei writes:
>
>> On 2015-10-14 5:58, Samuel M. Goldwasser wrote:
>>> ...
>>> To the original poster: You can probably pretyy much ignore what Phil
>>> and I have said. If your path length difference is small compared to
>>> 150 mm (the cavity length of the 1107 tube), then it will be fine. ;-)
>>>
>> Thank you for all responded with helpful comments. I measure a glass
>> substrate with the ellipsometer, , and my concern is whether the laser
>> reflected from the front side and back side will interfere and take into
>> account as one light. Glass thickness will not exceed 5mm, so I can
>> safely take that for granted. But the ellipsometer still does not show a
>> regular pattern (eye-glass shaped) like one-side reflection, which I am
>> still confused.
>
> They will interfere, but the result won't be detectably different than
> if the laser had an infinite coherence length because it is such a small
> difference.
>
> Not knowing the specs of your instrument, I can't say whether that's a
> problem. Do you have the manual?
>
Yes I have the manual. The situation I am considering is not common in
ellipsometry, because normally an optically semi-infinite substrate is
used. If the substrate have a thickness less than coherent length, then
it should be treated as an layer. But in my situation, that layer is too
thick (mm instead of normally nm), and laser is the light source, so the
reflection beams from front and back side actually split apart. So
interference may just happen at their intersection, and the signal
analyzer may get is the superposition of two incoherent lights and a
interfered light. That seems really complicated.
The measurement situation:
http://postimg.org/image/44b1ze9hb/
--
Regards,
Lu Wei
PGP key ID: 0x92CCE1EA
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