Sub-Doppler resolution mid-infrared spectroscopy using a difference-frequency-generation source spectrally narrowed...

Area of Science:

• Laser Spectroscopy
• Quantum Optics
• Molecular Spectroscopy

Background:

• Narrow spectral linewidth is crucial for high-resolution spectroscopy.
• Difference-frequency-generation (DFG) sources offer tunability in the mid-infrared.
• Achieving narrow linewidths in DFG sources has been a challenge.

Purpose of the Study:

• To reduce the spectral linewidth of a 3.28 μm DFG source.
• To demonstrate laser linewidth transfer from a pump laser to a DFG source.
• To enable high-precision molecular spectroscopy of methane.

Main Methods:

• Utilized a laser linewidth transfer technique.
• Employed an optical frequency comb with a broad servo bandwidth.
• Transferred the narrow linewidth of a 1.06 μm Nd:YAG pump laser to a 1.57 μm external-cavity diode laser signal laser.

Main Results:

• Reduced the DFG source spectral linewidth to 3.5 kHz.
• Recorded the Lamb dip of the methane ν3 band R(2) E transition with a 21 kHz molecular spectral linewidth.
• Achieved absolute frequency calibration of the recorded spectrum.

Conclusions:

• Demonstrated a viable method for generating narrow-linewidth mid-infrared light.
• The developed DFG source is suitable for high-resolution molecular spectroscopy.
• This technique advances precision measurements in molecular physics.