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A. Dubietis coauthored the 1992 paper introducing chirped and stretched pulse parametric amplification in beta barium borate with G. Jonušauskas and A. Piskarskas. Its publisher Abstract reports compressed pulses of $70\mathrm{fs}$ and approximately $0.9\mathrm{GW}$ output power.^[ref]

The approach connects optical parametric amplifier with the central logic of chirped pulse amplification: amplify a temporally stretched signal, then compensate its spectral phase to recover a short optical pulse. The amplified optical bandwidth matters because a narrow spectrum cannot support an arbitrarily short pulse, even with ideal compression.

For an original Gaussian pulse example, an intensity full width at half maximum $\Delta t$ and ordinary-frequency intensity width $\Delta \nu$ satisfy $\Delta t\Delta \nu =2\ln 2/\pi \approx 0.441$ for a transform-limited pulse. Thus a Gaussian spectrum of width $10\mathrm{THz}$ supports a transform-limited intensity duration of about $44.1\mathrm{fs}$. A measured duration of $100\mathrm{fs}$ with that same spectrum would have time-bandwidth product one, exceeding the transform-limited value. Residual spectral phase can account for such broadening, though the product alone does not uniquely reconstruct that phase. The stipulated bandwidth and durations are illustrative, not additional experimental data from the paper.

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.^[ref]

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.

Donna Strickland co-developed chirped pulse amplification with Gérard Mourou. In their 1985 experiment, an optical fiber broadened and stretched the optical pulse; amplification was followed by recompression using diffraction gratings. The reported output reached millijoule energies with a duration of about $2\times 10^{-12}$ seconds. Stretching before amplification reduced the peak power encountered by the amplifier, making the final short, energetic optical pulse possible.^[ref]

A physicist researching laser physics.^[ref]

Gérard Mourou and Donna Strickland demonstrated chirped pulse amplification: stretch a short optical pulse, amplify it while its peak power is lower, then recompress it. This addresses the self-focusing that limits direct amplification of an intense short optical pulse. Their 1985 system used an optical fiber for stretching and a diffraction grating compressor after amplification. The approach separates the gain in energy from the largest peak power inside the amplifier.^[ref]

A physicist researching laser physics.^[ref]

Optical parametric chirped pulse amplification combines the stretch–amplify–compress sequence of chirped pulse amplification with an optical parametric amplifier. A stretched signal pulse overlaps a strong pump pulse in a nonlinear crystal. Three-wave mixing transfers pump energy into the signal and an idler; subsequent pulse compression brings the amplified signal's frequencies back together. The pump supplies the added energy, rather than a stored population inversion.^[ref]

A. Dubietis, G. Jonušauskas and A. Piskarskas reported chirped and stretched pulse parametric amplification in beta barium borate in 1992. Their paper establishes a concrete early implementation of the parametric route; its published title identifies the nonlinear crystal.^[ref]

For pump, signal and idler angular frequencies, the conversion obeysEfficient amplification also requires phase matching, so contributions generated along the crystal reinforce. For collinear propagation the corresponding wave-vector relation is $k_p=k_s+k_i$; a noncollinear geometry requires the vector relation. Crystal dispersion and the chosen geometry determine which signal bandwidth is efficiently amplified.

An original energy-accounting example uses a 515-nanometre pump and an 800-nanometre signal. Their vacuum wavelengths giveSuppose 40 percent of a 2-millijoule pump is converted into signal–idler pairs, with negligible seed energy and other losses in this chosen model. Each conversion divides photon energy according to frequency, so the added signal energy isThe idler receives the remaining 0.285 millijoule. Assigning all depleted pump energy to the signal would violate this accounting.

If a compressor transmits 80 percent of that signal energy into a 50-femtosecond Gaussian pulse, the surviving energy is 0.412 millijoule. The chirped pulse amplification energy budget givesThese are stipulated teaching values, not a reconstruction of the 1992 experiment. Stretching lowers peak power during amplification; it does not remove the need to manage pump intensity or optical damage.

A useful apparatus check varies pump–signal delay while recording signal and idler spectra and energies. This tests temporal overlap and the frequency-conversion relation. Measuring the compressed pulse separately checks whether amplified bandwidth and residual spectral phase support the claimed pulse duration. Gain alone does not demonstrate successful compression, and an energy measurement alone does not establish peak power.

Write the optical system's spectral response as $A(\omega )e^{i\varphi (\omega )}$. Expanding its spectral phase around the pulse's central angular frequency givesThe group delay is ${\varphi }^{(1)}=d\varphi /d\omega$, with units of time. The linear spectral phase term delays the pulse envelope by this amount. The group delay dispersion is ${\varphi }^{(2)}=d^2\varphi /d{\omega }^2$, with units of time squared. It makes the group delay frequency dependent: $t_g(\omega )\simeq {\varphi }^{(1)}+{\varphi }^{(2)}(\omega -{\omega }_0)$. Positive group delay dispersion delays higher frequencies more and gives positive chirp. A nonzero quadratic spectral phase broadens an initially transform-limited pulse; applied to an already chirped pulse, a suitable opposite sign can compress it.

In chirped pulse amplification, an ultrashort seed pulse first passes through a dispersive stretcher, often a grating-based system. This correlates frequency with arrival time and increases pulse duration while approximately preserving pulse energy, thereby lowering peak intensity. An optical amplifier can then increase pulse energy without exposing the gain medium to the original short pulse's enormous peak intensity, reducing optical damage and unwanted nonlinear phase accumulation. A final dispersive compressor, typically using gratings, cancels the accumulated spectral phase to recover a short, high-energy pulse. The essential components are therefore a short-pulse source, stretcher, amplifier and matched compressor; spectral gain bandwidth and higher-order dispersion limit the achievable compression.