Second Harmonic Generation Electric Field Triplet Interferometry for Absolute Phasing.

Area of Science:

• Nonlinear optics
• Ultrafast spectroscopy
• Surface science

Background:

• Second harmonic generation (SHG) is a key nonlinear optical process.
• Accurate phase and intensity measurements are crucial for SHG spectroscopy.
• Existing methods often require external reference materials.

Purpose of the Study:

• To introduce a novel SHG electric field triplet interferometry technique.
• To enable internal calibration of SHG intensity and precise signal phase determination.
• To overcome limitations of traditional SHG measurement protocols.

Main Methods:

• Utilizing three mutually coherent ultrafast pulses (Sample Signal, Reference Oscillator, Local Oscillator).
• Employing a common-path interferometer with controllable relative phases.
• Subtracting a ROLO phase from the SIROLO interferogram to obtain the signal phase.
• Internally calibrating SHG intensity using reflected fundamental light field.

Main Results:

• Successfully measured the signal phase (ϕ_SI) with high accuracy.
• Demonstrated on-the-fly calibration of SHG intensity, independent of experimental fluctuations.
• Validated the method against standard materials (z-cut α-quartz, fused silica, hematite nanolayers) across multiple interferometers.

Conclusions:

• The developed SHG electric field triplet interferometry offers a robust and self-calibrating approach.
• This method eliminates the need for sample exchange with reference materials.
• The technique is broadly applicable to other second-order nonlinear spectroscopies like sum-frequency generation.