The quantum-limited comb lineshape of a mode-locked laser: Fundamental limits on frequency uncertainty

TL;DR

This paper analyzes the fundamental quantum noise limits on the spectral lineshape and frequency uncertainty of a mode-locked Ti:sapphire laser, providing insights into the ultimate precision achievable in optical frequency measurements.

Contribution

It models the quantum-limited comb lineshape and residual phase noise, incorporating experimental parameters and feedback effects, to determine fundamental frequency measurement limits.

Findings

Calculated the quantum-limited comb lineshape across the laser spectrum.

Quantified the residual phase noise spectrum due to quantum noise and feedback.

Estimated the minimum frequency uncertainty in optical heterodyne detection constrained by quantum noise.

Abstract

We calculate the quantum-limited shape of the comb lines from a mode-locked Ti:sapphire laser using experimentally-derived parameters for the linear response of the laser to perturbations. The free-running width of the comb lines is found across the laser spectrum. By modeling the effect of a simple feedback loop, we calculate the spectrum of the residual phase noise in terms of the quantum noise and the feedback parameters. Finally, we calculate the frequency uncertainty in an optical frequency measurement if the limiting factor is quantum noise in the detection of the optical heterodyne beat.