Volume 4, Number 2 May/June 1996
Today, images and recordings are performed in the near-infrared of the light spectrum, but the search for higher resolution and clarity could change that, specifically for medical applications which require high resolutions. The required higher resolution can be achieved using a shorter wavelength such as ultraviolet (UV), but currently there is no compact UV source that can be used to record at that wavelength. Existing commercial UV lasers are too bulky, unreliable, inefficient, and costly.
A team composed of Polaroid Corporation (Cambridge, Mass.), Lasertron, Inc. (Burlington, Mass.), and NASA Jet Propulsion Laboratory (Pasadena, Calif.) under the Aerospace Industry Technology Program (AITP) will be developing a compact, efficient, wavelength selectable, continuous-wave (CW) UV laser source (100 mW) and compatible recording medium sensitive to the UV wavelength.
This technology is essential for Polaroid commercial products and certain NASA missions. Targeted commercial applications are primarily in the high-end reprographic imaging segment and recording of the dry printing industry. However, other applications such as storage density for read and write applications in the optical recording industry will also be greatly impacted.
NASA missions requiring a laser suitable for space imaging and spacecraft flight will also greatly benefit from this project. Such a laser will enable remote sensing of the atmosphere and soil in the ultraviolet region, fluorescent spectroscopy or bioanalysis of soils and other targets, which could not be done otherwise.
The team is pursuing an approach using frequency doubling of single spatial and longitudinal mode near-infrared diode lasers with a wavelength of less than 800 nanometers. The general approach will be to use an external build-up cavity containing a nonlinear crystal that is phase matched for second harmonic generation (SHG) of the particular laser diode wavelength of interest. The diode laser beam is injected into the external cavity that is maintained in resonance with the diode laser. With this approach, the nonlinear crystal in the cavity experiences power levels that are up to two orders of magnitude higher than the original output power of the diode laser. This power level is built up in the cavity by constructive interference. Although this is a well-known technique for efficient doubling of CW diode lasers, output power levels obtained so far are over an order of magnitude below that required for printing applications. Therefore, diode lasers with substantially higher power in a single-mode are required in conjunction with significant improvements in efficiency of the SHG process. Moreover, the UV lasers will have to be very rugged and operate well under mechanical vibration and acoustic noise environments typically present with the printers (see figure above).
Lasertron, Inc. is responsible for development of high-power, near-infrared diode lasers. New approaches to laser development are being undertaken to achieve the targeted goals within the first year of this two-year program.
JPL and Polaroid are designing the resonant build-up cavity. Also, JPL is developing a technique of maintaining the cavity in resonance with the laser and designing the electronics for robust locking of the cavity in resonance.
Polaroid Corporation is experimentally evaluating SHG crystals and different cavity architectures and will integrate the high-power diode laser with the selected cavity to generate the required UV laser powers. The laser will then undergo substantial testing and evaluation by Polaroid Corporation for use in high density information storage, holographic optical memories on photorefractive or photopolymeric materials, and other commercial products.
This project is managed for NASA by the Jet Propulsion Laboratory in Pasadena, California.
For more information, contact Carl Ray at NASA Headquarters. Phone: 202/358-4652, E-mail: cray@hq.nasa.gov Or contact Neville Marzwell at the Jet Propulsion Laboratory. Phone: 818/354-6543, E-mail: Neville.Marzwell@jpl.nasa.gov Please mention that you read about it in Innovation.
