Is the nature of light observed only indirectly after its interaction with matter? We currently lack an experimental technique which would isolate the nature of light without the use of matter i.e., a detector. We will present additional experiments which, although again indirect, may reveal new understandings (but mostly more questions) about the nature of light. This talk will not report research results, but rather be an invitation for others to conduct similar such measurements as will be proposed. Past measurements have measured no absorption of radiation in the dark fringe (concluding no light is present due to canceling of the fields). Does the radiation in a dark fringe cause stimulated emission? What are the photon statistics in a dark fringe?
Laser induced fluorescence has been observed in off the shelf optical materials when pumped with a copper vapor laser at 510 nm and 578 nm as well as when pumped with a doubled Nd:YAG laser at 532 nm at average irradiance levels of 80 and 10 watts/cm<SUP>2</SUP> respectively. The fluorescence spectra was observed using an avalanche photodiode photon counter and ranges from the excitation wavelength to 1100 nm. Lifetimes ranging from less than a microsecond to a millisecond, depending on the type and grade of optical material. The fluorescence is attributed to both impurities as well as intrinsic defects in the material. Fluorescence is observed in every type of material tested including UV grade fused silica, although such materials fluoresce several orders of magnitude less than standard optical grade materials such as flints and crowns.
The ability to acquire, track, and accurately direct a laser beam to a satellite is crucial for power-beaming and laser-communications. To assess the state of the art in this area, a team consisting of Air Force Phillips Laboratory, Sandia National Laboratories, and COMSAT Corporation personnel performed some laser beaming demonstrations to various satellites. A ruby laser and a frequency-doubled YAG laser were used with the Phillips Lab Starfire Optical Range (SOR) beam director for this activity. The ruby laser projected 20 J in 6 ms out the telescope with a beam divergence that increased from 1.4 to 4 times the diffraction limit during that time. The doubled YAG projected 0.09 J in 10 ns at 20 Hz. The SOR team demonstrated the ability to move rapidly to a satellite, center it in the telescope, then lock onto it with the tracker, and establish illumination. Several low-earth-orbit satellites with corner- cube retro-reflectors were illuminated at ranges from 1000 to 6000 km with a beam divergence estimated to be about 20 (mu) radians. The return signal from the ruby laser was collected in a 15-cm telescope, detected by a photomultiplier tube, and recorded at 400 kHz. Rapid variations in intensity (as short as 15 microsecond(s) ) were noted, which may be due to speckles caused by phase interference from light reflected from different retro-reflectors on the satellite. The return light from the YAG was collected by a 35-cm telescope and detected by an intensified CCD camera. The satellite brightened by about a factor of 30 in the sunlight when the laser was turned on, and dimmed back to normal when the 50-(mu) radian point- ahead was turned off. The satellite was illuminated at 1 Hz as it entered the earth's shadow and followed for about 10 seconds in the shadow. In another demonstration, four neighboring GEO satellites were located and centered in succession with a 3.5-m telescope at a rate of about 16 seconds per satellite.
A team of Phillips Laboratory, COMSAT Laboratories, and Sandia National Laboratories plans to demonstrate state-of-the-art laser-beaming demonstrations to high-orbit satellites. The demonstrations will utilize the 1.5-m diameter telescope with adaptive optics at the AFPL Starfire Optical Range (SOR) and a ruby laser provided by the Air Force and Sandia (1 - 50 kW and 6 ms at 694.3 nm). The first targets will be corner-cube retro-reflectors left on the moon by the Apollo 11, 14, and 15 landings. We attempt to use adaptive optics for atmospheric compensation to demonstrate accurate and reliable beam projection with a series of shots over a span of time and shot angle. We utilize the return signal from the retro- reflectors to help determine the beam diameter on the moon and the variations in pointing accuracy caused by atmospheric tilt. This is especially challenging because the retro-reflectors need to be in the lunar shadow to allow detection over background light. If the results from this experiment are encouraging, we will at a later date direct the beam at a COMSAT satellite in geosynchronous orbit as it goes into the shadow of the earth. We utilize an onboard monitor to measure the current generated in the solar panels on the satellite while the beam is present. A threshold irradiance of about 4 W/m<SUP>2</SUP> on orbit is needed for this demonstration.
Conference Committee Involvement (2)
The Nature of Light: What are Photons? V
26 August 2013 | San Diego, California, United States
The Nature of Light: What are Photons? IV
22 August 2011 | San Diego, California, United States