LTM >> Background
Figure 1: The LTM design. A standing wave of laser light traps particles.
Image: A. Labeyrie.
"Laser trapped mirrors [may] be a practical solution to the problem of building large, low-mass optical systems in space."
Beams emitted in opposite directions by a laser strike two deflectors. The reflected light produces a series of parabolic fringe surfaces [Fig. 2]. Through diffractive and scattering forces, dielectric particles are attracted towards bright fringes while metallic particles move into dark fringes. By ramping the laser wavelength, particles can be swept into the central fringe, resulting in a reflective surface in the shape of a mirror of almost arbitrary size. Very large aperture mirrors could be created with very low mass (a 35 m mirror would have a mass of 100 grams) and extremely high packing efficiency (5 cm
An LTM would have several other advantages. It could be deployed without large moving parts, has the potential to actively alter the mirror's shape, and the flexibility to change mirror "coatings" while in orbit. It also has the potential for fabricating "naturally" co-phased arrays of arbitrary shape [Fig. 3]. The design is resilient against meteoroid damage or other disturbances to the surface, since it can heal itself through optical forces.
The LTM should be diffraction limited at long wavelengths. For a trapping wavelength in the visible, e.g. 0.5 μm, and operating at 20 μm, the "flatness" of the mirror will be better than λ/80.
Figure 2 (left): A series of parabolic fringe surfaces. Image: A. Labeyrie.
Figure 3: The LTM design has the potential for fabricating "naturally" co-phased arrays of arbitrary shape. Image: A. Labeyrie.
