jliu@pender (.) (03/01/90)
>3. How would & what is the best way/method of containing the laser beam, after > it penatrates the material, OR if the beam is running & there isn't any > material to penatrate. Well, assuming that a lens is used to focus the laser beam at one point, you could place a solar cell beyond the focal point of the lens to recirculate the power pumped into the laser. Or, you can actually couple some of the beam energy back into the laser. Just suggestions... ------------------------------------------------------------------------- John C. Liu Univ. of Pennsylvania (Electrical Engineering Dept.) -------------------------------------------------------------------------
henry@utzoo.uucp (Henry Spencer) (03/02/90)
In article <21050@netnews.upenn.edu> jliu@pender (.) writes: >>3. How would & what is the best way/method of containing the laser beam, after >> it penatrates the material, OR if the beam is running & there isn't any >> material to penatrate. > >Well, assuming that a lens is used to focus the laser beam at one point, you >could place a solar cell beyond the focal point of the lens to recirculate >the power pumped into the laser... Remember that the best readily-available solar cells are only about 15% efficient, and that there are limits to how much light they can take without overheating and failing. Not workable, I'm afraid. -- MSDOS, abbrev: Maybe SomeDay | Henry Spencer at U of Toronto Zoology an Operating System. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
jliu@pender (.) (03/03/90)
In article <1990Mar1.183939.1108@utzoo.uucp> (Henry Spencer) writes: > >Remember that the best readily-available solar cells are only about 15% >efficient, and that there are limits to how much light they can take >without overheating and failing. Not workable, I'm afraid. The efficiency of a solar cell is a function of how much incident electromagnetic energy IN ALL FREQUENCIES is converted into electrical energy. In normal operation, any incident frequency with energy above the work function of the solar cell will excite photoelectrons. When they say a solar cell is 15% efficient, that does not mean that it converts only 15% of the energy in all frequencies to electrical power. Rather, the solar cell may have near perfect efficiency in the visible spectrum, but be much less efficient at lower frequencies. The 15% efficiency is the net efficiency over the entire spectrum of sunlight, which includes visible, uv, etc.. It is possible to fabricate solar cells which respond optimally at certain frequencies. Since a laser is inherently a monochromatic or quasi- monochromatic device, the solar cells can easily be tuned to the laser frequency. As for the other consideration, heat can be generated in solar cells by either a resistivity in the wires imbedded in the cell or by the creation of phonons (vibrational modes in the silicon crystal lattice). These characteristics, too, can be overcome by careful design, since only the range of frequencies of the laser light need be considered. -------------------------------------------------------------------------- John C. Liu | "To be a student is to be Univ. of Pennsylvania | morally handicapped." Philadelphia, PA 19104 | - JCL --------------------------------------------------------------------------