Pulse generation in Yb-doped polarization-maintaining fiber laser by nonlinear polarization evolution

We demonstrate a self-started,long-term stable polarization-maintaining mode-locked fiber laser based on the nonlinear polarization evolution technique.A polarized beam splitter is inserted into the cavity of the linear polarizationmaintaining fiber laser to facilitate self-started mode-locking.Pulses with single pulse energy of 26.9 nJ and average output power of 73.9 mW are obtained at the pump power of 600 mW.The transmission characteristics of artificial saturable absorber used in this laser are analyzed theoretically,the influence of the half-wave plate state on mode-locking is discussed,and the mode-locking range is obtained,which is well consistent with the experimental results.

Phase and direction dependence of photorefraction in a low-frequency strong circular-polarized plane wave

Contrary to the superposition principle, it is well known that photorefraction exists in the vacuum with the presence of a strong static field, a laser field, or a rotational magnetic field. Different from the classical optical crystals, the refractive index also depends on the phase of the strong electromagnetic field. We obtain the phase and direction dependence of the refractive index of a probe wave incident in the strong field of a circular-polarized plane wave by solving the Maxwell equations corrected by the effective Lagrangian. It may provide a valuable theoretical basis to calculate the polarization evolution of waves in the strong electromagnetic circumstances of pulsar or neutron stars.

Polarization evolution of vector beams generated by q-plates

The polarization evolution of vector beams(VBs) generated by q-plates is investigated theoretically and experimentally.An analytical model is developed for the VB created by a general quarter-wave q-plate based on vector diffraction theory.It is found that the polarization distribution of VBs varies with position and the value q.In particular,for the incidence of circular polarization,the exit vector vortex beam has polarization states that cover the whole surface of the Poincarésphere,thereby constituting a full Poincarébeam.For the incidence of linear polarization,the VB is not cylindrical but specularly symmetric,and exhibits an azimuthal spin splitting.These results are in sharp contrast with those derived by the commonly used model,i.e.,regarding the incident light as a plane wave.By implementing q-plates with dielectric metasurfaces,further experiments validate the theoretical results.

Coupling electro-mechanical behaviors in the interdigital electrode device of ferroelectrics

The electro-mechanical coupling behaviors of ferroelectric devices with interdigital electrodes may become complicated due to the material inhomogeneity and local field concentration under the complex working conditions.In this paper,a ferroelectric model,drawn from the typical interdigital electrode structure of a ferroelectric sensor,is established based on phase field theory,to study the polarization evolution and explore the evolution laws in ferroelectrics.Numerical results show that there appears ferroelectric creep even under an applied electric field below the coercive field value.Also,the configurational force theory is introduced to investigate the mechanical behaviors related to polarization switching in the ferroelectric samples with interdigital electrodes.It is found that configurational force and polarization have similar evolution laws in both time evolving and space distribution.And considering the configurational force as the driving force,it is possible to predict the potential direction of polarization evolution and explore its evolution mechanism in ferroelectrics,demonstrating the configurational force as a useful parameter for describing mechanical behavior during the polarization evolution and a powerful tool for investigating the evolution mechanism of microstructure with coupling effects in ferroelectric materials.