Originally Posted by reio-ta
That's not true, you still get brightness compression your way. In a mixed scene, you can't turn off the LASER but the portion of the screen that was originally black is no longer black. The only way to do this is with a scanning LASER. The way a LASER is used in this case is as a light bulb replacement. The only advantage contrast wise is you can stop down your iris so it's nearly a pin hole and yet still have a very bright screen. LCOS benefits greatly when the iris is made smaller. A conventional UHP or xenon lamp, the more you clamp down the iris, the lower the light output, but with a LASER that's no longer a problem.
Your absolutely right you will get brightness compression and the only way to get a CRT effect is with a scanning system if you have a high powered laser with a fast enough rise and fall time.
You can not stop your iris down to a pinhole because you will destroy your resolution at the screen because of diffraction Even if you have a scanning system , you will need a certain Fnumber at the exit side to get a small spot at the screen, that is why scanning laser systems use F theta lenses.
The contrast will increase because the laser light has a narrow bandwidth and the extinction ratio of the polarizers will increase
Although you do not want to focus the light directly on the screen See Gaskill, intro to Fourier Optics the spot size of a Gaussian Beam is without aberrations is given by 1.29 x wavelength X Fnumber
say you stop the system down to a .1mm pinhole and your 15 ft this from the screen. this will give you an F" of 45,000
This will result in a spot size of 35 mm. to keep diffraction from having effect on resolution and to keep edge scatter to a minimum i would probably set the aperture of the system at around 10 to 12 mm .35mm spot size which is about where the current system are set at.
I also do not think the the Novalux lasers are spatially coherent so I do not think you would use a pinhole to even scan the beam and even laser scanners expand the beam to focus the laser to a spot at the image plane
In a laser scanning system you set the stop of the system at the scanning mirror whether its a galvometric scanner, resonant scanner (super markets) or
rotating faceted mirror scanner (very nice but very expensive. the stop size is usually around 12mm and you try to fill the whole stop with the laser light.
You then put a lens in front of the beam called an f theta lens which linear translates the angle of the mirror to the point on the image plane. If you do not do this the dwell time will be different for different field points.
for projection systems for the home you would have to design a zoom fTheta lens. I am not sure it has ever been done but it would be fun to do.
IBM published a bunch a papers in the 1970s on laser scanning systems but you needed big gas argon lasers and acousto-optical modulators. It was all the rage for a while but just to expensive for the home.
You may be on to something!