Upconversion-based mid-infrared spectrometer using intra-cavity LiNbO₃ crystals with chirped poling structure

Area of Science:

• Optics and Photonics
• Spectroscopy
• Nonlinear Optics

Background:

• Mid-infrared (MIR) spectroscopy is crucial for compound characterization.
• Conventional MIR detectors suffer from thermal noise, limiting detectivity.
• Upconversion offers a path to sensitive MIR detection using near-visible detectors.

Purpose of the Study:

• To develop an upconversion-based spectroscopy scheme with enhanced bandwidth and reduced sampling time.
• To enable sensitive and low-noise detection of MIR light.

Main Methods:

• Utilized sum-frequency generation for upconversion from MIR to near-visible wavelengths.
• Employed lithium niobate (LiNbO3) crystals with chirped poling structure inside a laser cavity.
• Conducted numerical studies to analyze the efficiency-bandwidth relationship.

Main Results:

• Achieved simultaneous upconversion from 2.15 μm to 5.3 μm.
• Demonstrated ultra-short sampling times as low as 10.8 μs.
• Obtained an average signal-to-noise ratio exceeding 6000 at 1 s.
• Numerical and experimental results showed good agreement regarding efficiency and bandwidth.

Conclusions:

• The developed upconversion scheme provides an unprecedented combination of large bandwidth and short sampling time for MIR spectroscopy.
• This technique significantly improves MIR light detection sensitivity and reduces noise.
• The findings pave the way for advanced applications in compound characterization and sensing.