A developmental apparatus and process for the fabrication of photonic devices utilize intense, focused laser light projected and/or diffracted in controlled patterns. The apparatus and process can be used in a microgravitational environment to form microscopic three-dimensional device structures (e.g., filters or other periodic structures with characteristic dimensions of the order of a wavelength of light). The apparatus and process could also be used on Earth to fabricate devices with two-dimensional structures.
The apparatus is designed to generate and control the pondermotive effects of intense laser light on molecules and other small particles. These effects include radiation pressure and optical trapping forces, and are accompanied by secondary effects like dipole/dipole interactions. The process exploits these effects in order to arrange large numbers of such particles in patterns that correspond to the microscopic photonic-device structures that one seeks to fabricate.
The apparatus (see figure) includes a compact laser that generates a high-power-density beam, plus optics for either focusing the beam to a spot of adjustable size or else forming the beam into a desired pattern. The apparatus also includes a sample cell wherein the device is to be formed, external equipment (not shown in the figure) that provides controlled flows of depositional and fixative gases to the sample cell, microscopes fitted with video cameras for monitoring what happens in the sample cell, and three-dimensional (x,y,z) translation stages for the sample cell and for the optical components.
If, for example, a device is to be deposited on a glass plate, then the process begins with the preparation of a sample cell made from that plate (which becomes the rear plate of the cell) plus a second plate. The rear plate can be treated to enhance the adhesion of particles that are to be deposited on it. The two plates are separated by a small gap and sealed together at their edges to form the cell. A suspension of particles (typically with sizes of the order of 1 µm) is prepared and put into the cell. The laser is focused into the cell from the front side (in a gravitational field, this must be the top side). The pondermotive effects (plus gravitation, if any) push the particles onto the rear plate and arrange them in the desired pattern.
The process is not yet well defined. Preliminary experimental data have shown that crystallization in two-dimensional patterns can be achieved by controlling particle patterns as described above, but motion of the suspending fluid tends to disrupt the crystallization. Future development efforts would have to address this issue, plus the issue of fixation to make the processed material more stable.
Inquiries concerning rights for the commercial use of this invention should be addressed to
the Patent Counsel
Marshall Space Flight Center; (256) 544-0021.
Refer to MFS-31360.