Coherent artifact in modern pulse measurements

Area of Science:

• Ultrafast optics
• Nonlinear optics
• Quantum optics

Background:

• Characterizing ultrashort laser pulses is crucial for many scientific applications.
• Complex pulse structures and instabilities pose significant challenges for standard measurement techniques.
• Second-harmonic-generation (SHG) frequency-resolved optical gating (FROG) and spectral-phase interferometry for direct electric-field reconstruction (SPIDER) are common pulse measurement methods.

Purpose of the Study:

• To evaluate the performance of SHG FROG and SPIDER in measuring unstable trains of complex ultrashort pulses.
• To identify the limitations of each technique when faced with pulse instabilities and complex structures.
• To compare the accuracy of retrieved pulse parameters, such as duration and spectral phase.

Main Methods:

• Simulations of multishot intensity-and-phase measurements were performed.
• The study utilized SHG FROG and SPIDER techniques for pulse characterization.
• Analytical calculations were employed to confirm findings.

Main Results:

• Both SHG FROG and SPIDER failed to accurately resolve the pulse structure in unstable pulse trains.
• SHG FROG provided a reasonable estimate of the average pulse duration and indicated instability through trace discrepancies.
• SPIDER accurately retrieved the average spectral phase but significantly underestimated the average pulse duration, measuring only the coherent artifact.

Conclusions:

• Standard ultrashort pulse characterization techniques like SHG FROG and SPIDER have limitations when applied to unstable pulse trains.
• SPIDER's measurement of unstable pulse trains is primarily a coherent artifact, not a true representation of the pulse.
• Further development of diagnostic tools is needed for accurate characterization of complex and unstable ultrashort pulses.