Comment on “Time reversal of ultrafast waveforms by wave

August 15, 2000 / Vol. 25, No. 16 / OPTICS LETTERS 1207Comment on “Time reversal of ultrafast waveforms by wavemixing of spectrally decomposed waves”A. M. WeinerSchool of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907-1285Received March 16, 2000In a recent Letter [Opt. Lett. 25, 132 (2000)] the properties of two different techniques for time reversalof ultrafast optical waveforms were compared. Although both techniques, spectral phase conjugation andspectral inversion, perform the same function for real pulses, for pulses with complex envelope functions itwas asserted that only spectral inversion gives true time reversal. I argue here for a different interpretation.© 2000 Optical Society of AmericaOCIS codes: 320.0320, 320.5540, 320.7110, 070.4340, 190.5040, 190.4380.1–3Several techniques have been investigated for time Now we consider spectral phase conjugationreversal of ultrafast optical waveforms. A recent pa- (SPC). The spectral amplitude of the output wave-1 per reported an investigation of two different spectral form is given by S v S v, again for very shortSPCnonlinear optics approaches: spectral inversion and reference pulses. The envelope function in the timespectral phase conjugation (the latter is a real-time domain is given bys t s 2t, which correspondsSPC2,3version of spectral holography ). The results were to the correct time-reversed electric field in Eq. (2).interpreted to show that ...