= Chirped pulse amplification
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= CPA
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<Chirped pulse amplification> increases an <optical pulse>'s <energy> while keeping its <peak power> lower during amplification: stretch the pulse, amplify it, then compress it. A <chirp> is a changing instantaneous <frequency>. Stretching separates the arrival times of different <frequencies>; <pulse compression> brings their contributions back together. The gain medium supplies <energy>, whereas the compressor concentrates the surviving <energy> into a shorter time.
<Donna Strickland> and <Gérard Mourou> demonstrated <chirped pulse amplification> at Rochester in 1985. Their experiment used an <optical fiber>, a regenerative amplifier and a <diffraction grating> compressor.<Compression of amplified chirped optical pulses by Donna Strickland and Gérard Mourou>[Strickland and Mourou, corrected December 1985 paper, pp.219–221]{ref}
\Image[/chirped-pulse-amplification-stretch-amplify-compress.png]
{title=Stretch, add energy, then recover a short pulse}
{description=Original functional <chirped pulse amplification> diagram using chosen <Gaussian functions> for pulse <power>. The common time axes show the stretching; each vertical axis has its own labelled scale. The idealized amplifier has flat <optical gain> across the occupied spectrum, and the compressor transmits 80 percent of the incident <energy>. These are teaching assumptions, not a reconstruction of the 1985 apparatus or a measured pulse trace.}
The useful idea is to arrange where the large <peak power> occurs. Lower <light intensity> in the amplifier reduces unwanted <self-focusing> and <self-phase modulation>; the compressed output can still drive strong <nonlinear optics>. Stretching does not remove every damage mechanism, and compression does not manufacture <energy>.
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