Comments on ``A study of compressed spatially non‐Gaussian optical pulses from mode‐locked lasers''

摘要

The above paper by Kim et al. states that part of the nonlinearity of frequency sweep that we measured in picosecond pulses by dynamic spectroscopy techniques is caused by instrumental effects in a grating pair due to the presence of transverse modes. We would like to make the following comments: (i) The measurements were made with a fast spectrometer rather than with a pair of diffraction gratings. (ii) Transverse modes affect our spectrometer measurements only to the extent of reducing the resolving power by 2%. (iii) The frequency‐dependent group delay in the fast spectrometer has been properly accounted for in our earlier publications. (iv) In deriving their prediction of an instrumental contribution to apparent nonlinearity of frequency sweep, Kim et al. use an incorrect equation that describes a pulse crossing its time‐reversed image, which is not experimentally realizable. (v) The tilted wave packets that we studied with two‐photon fluorescence techniques are unrelated to the tilted wave packets discussed by Kim et al. Those described by Kim et al. would be difficult to observe experimentally. (vi) In our pulse compression experiments that used a pair of gratings, transverse mode effects were rendered negligible by the optical design. We assert that our measurements of average chirp characteristics of trains of mode‐locked pulses have been properly interpreted by us.