Amplitude fluctuations in the two-level and four-level models of a laser

M. Arjona, Ferran Laguarta, Jaume Pujol +1 more

Naveen K. Singh, Richard D’Souza, Q. V. Lawande +1 more

Yanpeng Zhang, Chenli Gan, Shahid Munir Farooqi +3 more

Four-level polarization beats (FLPBs) with broadband noisy light are investigated by use of chaotic field, phase-diffusion, and Gaussian-amplitude models. The polarization beat signal is shown to be particularly sensitive to the statistical properties of the Markovian stochastic light fields with arbitrary bandwidth. Different stochastic models of the laser field affect only the fourth-order coherence functions. The constant background of the beat signal originates from the amplitude fluctuation of the Markovian stochastic fields. The Gaussian-amplitude field shows fluctuations larger than the chaotic field, which in turn exhibits fluctuations much larger than for the phase-diffusion field with pure phase fluctuations caused by spontaneous emission. It is also found that the asymmetric behaviors of the polarization beat signals due to the unbalanced dispersion effects between the two arms of an interferometer and to the Doppler width do not affect the overall accuracy when FLPBs are used to measure the energy-level difference between two states that are dipolar forbidden from the ground state.

L. A. Pokrovskii, Alexander M. Khazanov

Yanpeng Zhang, Liqun Sun, Tiantong Tang +1 more

We have employed chaotic and phase-diffusion models to study the effects of laser fourth-order coherence on polarization beats with phase-conjugation geometry in a four-level system (PBFS). We found that the temporal behavior of the beat signal depends on the stochastic properties of the lasers and the transverse relaxation rate of the transition. The modulation terms of the beat signal depend on the second-order coherence function, which is determined by the laser line shape. Inasmuch as different stochastic models of the laser field affect only the fourth-order coherence function, they have little influence on the general temporal modulation behavior of the beat signal. The different roles of phase fluctuation and amplitude fluctuation are pointed out. The cases that pump beams have either narrow-band or broadband linewidth are considered, and it is found that for both cases a Doppler-free precision in the measurement of the energy-level difference between two states that are dipolar forbidden from the ground state can be achieved. We also discuss the difference between the PBFS and ultrafast modulation spectroscopy from a physical viewpoint.

M. Lax, Horace P. Yuen