Femtosecond broadband fluorescence upconversion spectroscopy: Spectral coverage versus efficiency

Area of Science:

• Nonlinear optics
• Spectroscopy
• Femtochemistry

Background:

• Sum frequency mixing (SFM) is a nonlinear optical process.
• Femtosecond fluorimeters utilize SFM for time-resolved fluorescence measurements.
• Optimizing SFM efficiency and spectral coverage is crucial for fluorimeter performance.

Purpose of the Study:

• To quantify the upconversion efficiency of SFM in a femtosecond fluorimeter.
• To evaluate two distinct crystal orientations for optimal performance.
• To assess the impact of orientation on spectral coverage and measurement accuracy.

Main Methods:

• Sum frequency mixing of fluorescence and ~1300 nm gate pulses using a beta-barium borate crystal.
• Non-collinear type II phase-matching geometry.
• Measurement of upconversion efficiency as a function of fluorescence wavelength for fixed phasematching angles.

Main Results:

• Two crystal orientations (A and B) were investigated.
• Orientation A demonstrated approximately three times higher efficiency than orientation B.
• Orientation B provided broader spectral coverage (420-750 nm) with less gate scatter.

Conclusions:

• The choice of crystal orientation impacts the trade-off between efficiency and spectral range in femtosecond fluorimetry.
• Orientation A is suitable for monitoring subtle changes in stationary emission bands.
• Orientation B is advantageous for broad spectral coverage and reduced time-zero scatter.