Amplitude-squeezed, frequency-modulated, tunable, diode-laser-based source for sub-shot-noise FM spectroscopy.

Area of Science:

• Atomic, Molecular, and Optical Physics
• Laser Physics
• Spectroscopy

Background:

• Diode lasers are crucial for various spectroscopic applications.
• Achieving low noise levels and high spectral purity is essential for sensitive measurements.
• Amplitude squeezing offers a route to surpass the standard quantum limit in optical measurements.

Purpose of the Study:

• To develop a frequency-modulated, tunable, amplitude-squeezed diode laser source.
• To utilize this source for high-sensitivity frequency-modulated (FM) spectroscopy.
• To demonstrate noise reduction below the shot-noise limit.

Main Methods:

• Constructed a laser system using injection locking between two diode lasers.
• A frequency-stabilized, current-modulated diode laser served as the master.
• A free-running diode laser acted as the slave, adopting the master's spectrum and enhanced squeezing.

Main Results:

• The injection-locked slave laser exhibited a suppressed residual amplitude modulation (AM) by over 50 dB.
• Amplitude squeezing in the slave laser beam was enhanced by suppressing unwanted sidemodes.
• The developed system achieved a measurement noise floor 0.8 dB below the shot-noise level.

Conclusions:

• The developed diode laser source is effective for high-precision FM spectroscopy.
• Injection locking is a viable technique for enhancing amplitude squeezing and spectral purity.
• The demonstrated noise reduction opens possibilities for more sensitive quantum optical measurements.