High-efficiency multilayer-dielectric diffraction gratings
The ability to produce short laser pulses of extremely high power and high irradiance, as is needed for fast ignitor research in inertial confinement fusion, places increasing demands on optical components such as amplifiers, lenses, and mirrors that must remain undamaged by the radiation. The higher refractive index in the center of an intense laser beam acts as a focusing lens. The resulting wavefront distortion, left uncorrected, eventually leads to catastrophic filamentation. Major advances in energy extraction and resulting increases in focused irradiance have been made possible by the use of chirped-pulse amplification (CPA), long used in radar applications and newly applied to optical frequencies. Optical-frequency CPA systems begin with a mode-locked oscillator that produces low-energy seed pulses with durations of ten to a few hundred femtoseconds. As a result of the classical uncertainty relation between time and frequency, these short pulses have a very broad frequency distribution. A pair of diffraction gratings (or other dispersive elements) lengthens the laser pulse and induces a time-varying frequency (or chirp). Following amplification, diffraction gratings compress the pulse back to nearly the original duration. Typically a nanojoule, femtosecond pulse is stretched by a factor of several thousand and is amplified by as much as 12 orders of magnitude before recompression. By producing the short pulse only after amplification, this technique makes possible efficient extraction of energy from a variety of broadband solid state materials. Achieving high focused irradiance from a pulse ultimately requires both high peak power and excellent beam quality. There is therefore a demand for diffraction gratings that produce a high-quality diffracted wavefront, have high diffraction efficiency, and exhibit a high threshold for laser damage.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- OSTI ID:
- 376954
- Report Number(s):
- UCRL-LR-105820-95; ON: DE96013181; TRN: 96:004685-0020
- Resource Relation:
- Other Information: PBD: Jun 1996; Related Information: Is Part Of Inertial confinement fusion. 1995 ICF annual report, October 1994--September 1995; PB: 407 p.
- Country of Publication:
- United States
- Language:
- English
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