In high-power laser system such as Petawatt lasers, the laser beam can be intense enough to result in saturation of nonlinear refraction index of medium. Based on the standard linearization method of small-scale self-focusing and the split-step Fourier numerical calculation method, we present analytical and simulative investigations on the hot-image formation in cascaded saturable nonlinear medium slabs, to disclose the effect of nonlinearity saturation on the distribution and intensity of hot images. The analytical and simulative results are found in good agreement. It is shown that, saturable nonlinearity does not change the distribution of hot images, while may greatly affect the intensity of hot images, i.e., for a given saturation light intensity, with the intensity of the incident laser beam, the intensity of hot images firstly increases monotonously and eventually reaches a saturation; for the incident laser beam of a given intensity, with the saturation light intensity lowering, the intensity of hot images decreases rapidly, even resulting in a few hot images too weak to be visible.
In high-power laser system such as Petawatt lasers, the laser beam can be intense enough to result in saturation of nonlinear refraction index of medium. We present an analytical and simulative investigation of hot image formation in an intense laser beam through a saturable nonlinear medium slab based on Fresnel-Kirchhoff diffraction integral and the standard split-step Fourier method. The analytical results are found in agreement with the simulative ones. It is shown that, hot images can still form in an intense laser beam through a saturable nonlinear medium slab, additionally, the saturable nonlinearity does not change the location of hot images, while may decrease the intensity of hot images, i.e., the intensity of hot images decreases with the saturation light intensity lowering, and can stop to increase with the intensity of the incident laser beam heightening due to saturation of nonlinearity. Moreover, variations of intensity of hot images with the obscuration type and the slab thickness are discussed.
We present a hybrid Poincaré sphere, whose eigenstates are defined as a pair of circularly polarized fundamental-mode Gaussian beam and a Laguerre-Gaussian beam, to describe the so-called full Poincaré beam. We also show that any desired full Poincaré beam over the hybrid Poincaré sphere via modulating the incident polarization state of light and two cascaded half-wave plates. This research provides an alternative way for charactering and manipulating the full Poincaré beam and an effective method to control the polarization state of light.
We report the demonstration of intrinsic spin Hall effect (SHE) of cylindrical vector beam. Employing a fan-shaped aperture to block part of the vector beam, the intrinsic vortex phases are no longer continuous in the azimuthal direction, and results in the spin accumulation at the opposite edges of the light beam. Due to the inherent nature of the phase and independency of light-matter interaction, the observed SHE is intrinsic. Modulating the topological charge of the vector beam, the spin-dependent splitting can be enhanced and the direction of spin accumulation is switchable.
Nanosecond-level pulses of specific shape is usually generated by stacking chirped pulses for high-power inertial
confinement fusion driver, in which nonlinear imaging of scatterers may damage precious optical elements. We present a
numerical study of the characteristics of nonlinear imaging of scatterers in broadband laser stacked by chirped pulses to
disclose the dependence of location and intensity of images on the parameters of the stacked pulse. It is shown that, for
sub-nanosecond long sub-pulses with chirp or transform-limited sub-pulses, the time-mean intensity and location of
images through normally dispersive and anomalously dispersive self-focusing medium slab are almost identical; While
for picosecond-level short sub-pulses with chirp, the time-mean intensity of images for weak normal dispersion is
slightly higher than that for weak anomalous dispersion through a thin nonlinear slab; the result is opposite to that for
strong dispersion in a thick nonlinear slab; Furthermore, for given time delay between neighboring sub-pulses, the
time-mean intensity of images varies periodically with chirp of the sub-pulse increasing; for a given pulse width of
sub-pulse, the time-mean intensity of images decreases with the time delay between neighboring sub-pulses increasing;
additionally, there is a little difference in the time-mean intensity of images of the laser stacked by different numbers of
sub-pulses. Finally, the obtained results are also given physical explanations.
The phenomenon of hot image in high power lasers is closely related to the spatial uniformity of laser beams and the
running safety of laser systems. Here we study the formation of the second-order hot image of phase defect in the
high-power broadband laser system, special attention is payed to the role of bandwidth of incident beam in the formation
of the second-order hot image. It is shown that, as the laser bandwidth increases by either increasing the positive
temporal chirp or reducing the pulse duration the intensity of the second-order hot image decreases. However, as the
amount of negative chirp increases, the intensity of the second-order hot image increases first but decreases after
reaching a maximum value. The distance between the second-order hot image and the nonlinear medium is found to be
about half that between the phase defect and the nonlinear medium. The influence of phase shift caused by the phase
defect and nonlinear effect on the formation of the second-order hot image is also numerically studied.
Based on the angular spectrum theory of light propagation and the mean-field approximation, an expression for intensity
of hot image of the intense laser beam through a thick Kerr medium with gain and loss is obtained, beyond the
thin-medium approximation. Thereby the dependence of intensity of hot image on the thickness and gain/loss of medium
and the property of obscuration are identified analytically and numerically. It is shown that, for a given obscuration, the
intensity of hot image decreases as the medium thickness increases for definite B integral and increases monotonously
with the medium thickness for definite input power of laser beam. For definite output power of laser beam and gain/loss
of medium, the intensity of hot image firstly increases and subsequently decreases as the medium thickness increases.
Furthermore, it is shown that hot image from obscuration of phase modulation is more intense than that from obscuration
of pure amplitude modulation, even in the presence of medium gain and loss. As the size of obscuration increases, the
intensity of hot image first increases gradually, after reaching a maximum value, it decreases rapidly to a minimum