Measuring an ultrashort, ultraviolet pulse in a slowly responding, absorbing medium

Area of Science:

• Ultrafast optics
• Nonlinear spectroscopy
• Laser pulse characterization

Background:

• Frequency-resolved optical gating (FROG) is standard for ultrashort laser pulse measurement.
• High-frequency materials often exhibit absorption, limiting nonlinear optical response.
• Existing FROG techniques struggle with strongly absorbing media.

Purpose of the Study:

• To develop a method for measuring ultrashort UV pulses in strongly absorbing media.
• To adapt the induced-grating cross-correlation FROG (IG XFROG) technique for absorptive nonlinear-optical time-gating.
• To characterize UV pulses using absorption-based nonlinear optical effects.

Main Methods:

• Utilized IG XFROG with an 800 nm reference pulse to characterize 400 nm and 267 nm pulses.
• Employed Zinc Sulfide (ZnS) as a nonlinear-optical medium, which is absorptive at these UV frequencies.
• Separated phase-sensitive four-wave-mixing signals from incoherent responses by scanning pulse delays.
• Applied a modified generalized projections (GP) algorithm for phase retrieval.

Main Results:

• Successfully measured ultrashort UV pulses (400 nm and 267 nm) in a strongly absorbing medium (ZnS).
• Demonstrated the ability to detect and separate the instantaneous nonlinear optical signal.
• Extracted pulse amplitude and phase using a modified GP algorithm.
• Validated the method by measuring chirped UV pulses.

Conclusions:

• Absorption can effectively serve as a nonlinear-optical time-gate for ultrashort pulse measurement.
• IG XFROG is adaptable for characterizing UV pulses in absorptive materials.
• The technique shows promise for deeper UV pulse measurements due to the wavelength independence of interband absorption.