Coatings for laser detector etalons

An etalon for modulating a radiation signal, comprising:

• a substrate having a first major surface and a second, opposite major surface;
• and a plurality of dispersive coatings formed upon at least one of said major surfaces of said substrate, said plurality of dispersive coatings each having a spatially varying index of refraction profile through a depth thereof, the profile being selected for inducing a predetermined phase shift between two adjacent coatings;
• wherein said plurality of dispersive coatings are rugate coatings having a spatially varying index of refraction profile n(x) that varies in accordance with a sinusoidal function, wherein n(x) is give by the expression:
• n(x)=n.sub.o (1+.intg.H(n.sub.i K(x-x.sub.o)/n.sub.o u(K)) sin (Kx+.phi.(K))dK/K)
• where n.sub.o is equal to the average index of refraction, K=40.pi.n.sub.o /.lambda., [.phi.' is the internal angle in the coating] and .lambda. is the wavelength, where u(K)=4tanh.sup.-1 (R(K)).sup.178 is a number of cycles in the coating to achieve a desired reflectivity R(K), n.sub.1 is the peak deviation of the index from n.sub.o for a single wavelength, where .phi.(K) is the phase of reflected light as a function of K, where x is a distance into the coating, and where H is an envelope or apodizing function located at x.sub.o whose extent defines the region of index at the wavelength .lambda..

Apparatus for detecting coherent radiation, comprising:

• an etalon disposed for receiving coherent radiation, said etalon including a substrate having a first major surface and a second, opposite major surface, the first major surface having at least one step therein;
• a plurality of dispersive coatings formed upon at least one of said major surfaces of said substrate, said plurality of dispersive coatings each having a spatially varying index of refraction profile through a depth thereof, the profile being selected as a function of a height of said at least one step and for reducing a falloff in a modulation characteristic of said etalon due to a phase shift for coherent radiation at said at least one step;
• and
• detector means disposed relative to said etalon for detecting a presence of the coherent radiation;
• wherein said plurality of dispersive coatings are rugate coatings having a spatially varying index of refraction profile n(x) that varies in accordance with a sinusoidal function, wherein n(x) is give by the expression:
• n(x)=n.sub.o (1+.intg.H(n.sub.i K(x-x.sub.o)/n.sub.o u(K)) sin (Kx+.phi.(K))dK/K)
• where n.sub.o is equal to the average index of refraction, K=4.pi.n.sub.o /.lambda., [.phi.' is the internal angle in the coating ] and .lambda. is the wavelength, where u(K)=4tanh.sup.-1 (R(K)).sup.178 is a number of cycles in the coating to achieve a desired reflectivity R(K), n.sub.1 is the peak deviation of the index from n.sub.o for a single wavelength, where .phi.(K) is the phase of reflected light as a function of K, where x is a distance into the coating, and where H is an envelope or apodizing function located at x.sub.o whose extent defines the region of index variation at the wavelength .lambda..

Apparatus for detecting coherent radiation, comprising:

• an etalon disposed for receiving coherent radiation, said etalon including a substrate having a first major surface and a second, opposite major surface;
• a plurality of dispersive coatings formed upon at least one of said major surfaces of said substrate, said plurality of dispersive coatings each having a spatially varying index of refraction profile through a depth thereof, the profile being selected for inducing a predetermined phase shift in the coherent radiation between two adjacent coatings;
• and
• detector means disposed relative to said etalon for detecting a presence of the coherent radiation;
• wherein said plurality of dispersive coatings are rugate coatings having a spatially varying index of refraction profile n(x) that varies in accordance with a sinusoidal function, wherein n(x) is give by the expression:
• n(x)=n.sub.o (1+.intg.H(n.sub.i K(x-x.sub.o)/n.sub.o u(K)) sin (Kx+.phi.(K))dK/K)
• where n.sub.o is equal to the average index of refraction, K=4.pi.n.sub.o /.lambda.,[.phi.' is the internal angle in the coating] and .lambda. is the wavelength, where u(K)=4tanh.sup.-1 (R(K)).sup.178 is a number of cycles in the coating to achieve a desired reflectivity R(K), n.sub.1 is the peak deviation of the index from n.sub.o for a single wavelength, where .phi.(K) is the phase of reflected light as function of K, where x is a distance into the coating, and where H is an envelope or apodizing function located at x.sub.o whose extent defines the region of index variation at the wavelength .lambda..