Selective reflecting for laser projector
A projection screen for selectively reflecting light from a front projector. The screen includes an etalon coating structure with a first layer of reflective material, a second layer of dielectric material, and a third layer of partially reflective semiconductor material. The projection screen produces a reflection having an asymmetric-shaped response in the visible spectrum.
1. An apparatus for selectively reflecting a beam of light from a front projector, the apparatus comprising:
a projection screen that includes an etalon coating structure comprising:
a first layer comprising a generally reflective material;
a second layer positioned such that it is closer to the projector than the first layer, the second layer comprising a dielectric material; and
a third layer positioned such that it is closer to the projector than the second layer, the third layer comprising a generally partially reflective semiconductor material;
wherein the projection screen produces a reflection having asymmetrically-shaped reflective peaks in the visible spectrum, wherein the reflection percentage rolls off from the peaks to a local minimum in less than 20 nm as the wavelengths get shorter and wherein the reflection percentage rolls off from the peaks to a local minimum in greater than 50 nm as the wavelengths get longer.
2. An apparatus in accordance with claim 1 , wherein the reflection comprises at least two peaks in the visible spectrum.
3. An apparatus in accordance with claim 1 , wherein the third layer has an index of refraction between 2 and 6.
4. An apparatus in accordance with claim 1 wherein the third layer has an extinction coefficient between 0.2 and 2.
5. An apparatus in accordance with claim 1 , wherein the third layer has an index of refraction between 3.5 and 5 and an extinction coefficient between 0.4 and 1.5.
6. An apparatus in accordance with claim 1 , wherein the third layer comprises a mixture of Silicon and Germanium.
7. An apparatus in accordance with claim 6 , wherein the third layer comprises a mixture of approximately 50% Silicon and 50% Germanium.
8. An apparatus in accordance with claim 1 , wherein the third layer comprises Selenium.
9. An optical apparatus comprising:
a front projector;
a projection screen for selectively reflecting a beam of light from the front projector, the screen including an etalon coating structure comprising:
a first layer comprising a generally reflective material;
a second layer positioned such that it is closer to the projector than the first layer, the second layer comprising a dielectric material; and
a third layer positioned such that it is closer to the projector than the second layer, the third layer comprising a generally partially reflective semiconductor material; wherein the projection screen produces a reflection having an asymmetric-shaped spectral response in the visible spectrum, wherein the reflection percentage rolls off from the peaks to a local minimum in less than 20 nm as the wavelengths get shorter and wherein the reflection percentage rolls off from the peaks to a local minimum in greater than 50 nm as the wavelengths get longer, and
wherein the beam of light has three spectral peaks with full-width-half-maximum bandwidths of less than 20 nm.