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Ultrafast optics

Precise pulse characterization using SHG-FROG

Nature Reviews Physics volume 7, page 605 (2025)Cite this article

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Laser pulses with femtosecond durations are today routinely generated and used in a variety of scientific experiments and for applications in medicine and industry. Although one might assume that such short pulses are immune to distortions, that is not the case. The duration of a pulse is strongly affected by distortions in both intensity and phase. As it is often necessary to know the pulse duration, a precise measurement technique is required. The second-harmonic generation frequency resolved optical gating (SHG-FROG) technique, introduced by Kenneth DeLong and co-workers, was the first to enable the complete temporal characterization of weak ultrashort laser pulses using a simple setup, and it is still used today. Unlike intensity autocorrelation, an early pulse characterization technique, SHG-FROG also provides crucial phase information.

DeLong and co-workers demonstrated the capability of SHG-FROG to fully characterize a range of different pulses. First, they validated the technique by comparing the SHG-FROG result of a pulse with nearly flat spectral phase with an autocorrelation and spectral measurement of the same pulse. The retrieved pulse was in excellent agreement with the independent measurements. To further prove the validity and flexibility of the technique, DeLong and co-workers generated a pulse with a more complicated phase profile and demonstrated that SHG-FROG could measure this complicated pulse and retrieve all its characteristics. Finally, they introduced and validated a retrieval algorithm for SHG-FROG, which is still used to calculate the pulse characteristics from the experimental data. Overall, SHG-FROG allows one to directly observe and compare complex intensity and phase distortions with theoretical studies.

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References

Original article

  • DeLong, K. W., Trebino, R., Hunter, J. & White, W. E. Frequency-resolved optical gating with the use of second-harmonic generation. J. Opt. Soc. Am. B. 11, 2206–2215 (1994)

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Related article

  • Kane, D. J. & Trebino, R. Characterization of arbitrary femtosecond pulses using frequency-resolved optical gating. IEEE J. Quantum Electron. 29, 571–579 (1993)

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Authors and Affiliations

  1. Max Planck Institute for the Science of Light, Erlangen, Germany

    Max Kieker

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  1. Max Kieker
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Correspondence to Max Kieker.

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The author declares no competing interests.

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Kieker, M. Precise pulse characterization using SHG-FROG. Nat Rev Phys 7, 605 (2025). https://doi.org/10.1038/s42254-025-00884-8

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