How to Determine Wavelengths for Half Wave Plate?

[lavenderblue]

Hey, I've been asked to find the minimum thickness for a slab of crystalline sapphire. The equation for the half wave plate is :

d(ne-no) = (m+1/2)*lambda

I found the minimum by using the fact that m=0

It then asks what the other wavelengths are which will allow the plate to act as a Half wave plate.
Do I just plug integers in starting from 1 or is that wrong?
Thanks :)

 

[naresh]

Yes, for shorter wavelengths, you can get retardations of 3/2 waves, 5/2 waves etc. - which are equivalent to half wave shifts.