Raman despeckling with spectral control
An apparatus and method for controlling the spectrum of stimulated Raman scattering that is used for despeckling of digitally projected images. The stimulated Raman scattering is utilized to add wavelength diversity for reduced speckle and to change the color of the light to a more desirable combination of wavelengths. Digital projection with color-sequential projectors may be enabled by alternately switching the Raman spectrum between green and red. Improved projector transmission may be achieved by minimizing the amount of yellow light generated in the Raman spectrum.
1. An optical apparatus comprising:
a pulsed green laser;
a Raman-shifting device; and
a digital projector;
wherein the pulsed green laser generates a green light with a light pulse that illuminates the Raman-shifting device;
the light pulse is shaped in time to generate a desired spectrum from the Raman-shifting device,
the desired spectrum illuminates the digital projector;
the light pulse is shaped in time to be a square shape;
the desired spectrum is red; and
the light pulse is shaped in time to alternate between a square shape of a first amplitude and a square shape of a second amplitude; the first amplitude is different than the second amplitude; and the desired spectrum alternates between green light and red light.
2. The apparatus of claim 1 wherein the digital projector comprises a single light valve; and the single light valve forms a full color digital image by synchronizing the single light valve with a source of blue light and with the desired spectrum that alternates between green light and red light.
3. A method of despeckling comprising:
generating a pulsed green laser light;
Raman-shifting the pulsed green laser light to generate a Raman-shifted laser light;
using the Raman-shifted light to illuminate a digital projector; and
projecting a digital image with the digital projector;
wherein the pulsed green laser light has a light pulse that is shaped in time to Raman-shift the laser light to a desired spectrum;
the light pulse is shaped in time to be a square shape;
the desired spectrum is red; and
the light pulse is shaped in time to alternate between a square shape of a first amplitude and a square shape of a second amplitude; the first amplitude is different than the second amplitude; and the desired spectrum alternates between green light and red light.
4. The method of claim 3 wherein the digital projector comprises a single light valve; and the single light valve forms a full color digital image by synchronizing the single light valve with a source of blue light and with the desired spectrum that alternates between green light and red light.