Laser lines at 635 nm or longer (ideally 647 nm) are preferred for red, giving
energy-efficient, bright, rapid-motion images with rich, full film-comparable colors.
Green and blue lines are used too-and cyan retained for best color mixing, an extra
light-power boost, and aid in speckle suppression. Speckle is suppressed through
beam-path displacement-by deflecting the beam during projection, thereby avoiding
both absorption and diffusion of the beam while preserving pseudocollimation (noncrossing
rays). The latter in turn is important to infinite sharpness. Path displacement
is achieved by scanning the beam on the liquid-crystal valves (LCLVs), which also
provides several enhancements-in energy efficiency, brightness, contrast, beam
uniformity (by suppressing both laser-mode ripple and artifacts), and convenient
beam-turning to transfer the beam between apparatus tiers. Preferably deflection
is performed by a mirror mounted on a galvanometer or motor for rotary oscillation;
images are written incrementally on successive portions of the LCLV control stage
(either optical or electronic) while the laser "reading beam" is synchronized on
the output stage. The beam is shaped, with very little energy loss to masking,
into a shallow cross-section which is shifted on the viewing screen as well as
the LCLVs. Beam-splitter/analyzer cubes are preferred over polarizing sheets. Spatial
modulation provided by an LCLV and maintained by pseudocollimation enables imaging
on irregular projection media with portions at distinctly differing distances from
the projector-including domes, sculptures, monuments, buildings; waterfalls, sprays,
fog, clouds, ice; scrims and other stage structures; trees and other foliage; land
and rock surfaces; and even assemblages of living creatures including people.
