Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMultiple Fourier Component Analysis of X-ray Second Harmonic Generation in Diamond
330
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The unprecedented brilliance of X-ray free-electron lasers (XFELs) [1, 2] has enabled first studies of nonlinear interactions in the hard X-ray range. In particular, X-ray-optical mixing [3], X-ray second harmonic generation (XSHG) [4] and nonlinear Compton scattering (NLCS) [5] have been recently observed for the first time using XFELs. The former two experiments as well as X-ray parametric downconversion (XPDC)[6, 7] are well explained by nonlinearities in the impulse approximation[8], where electrons in a solid target are assumed to be quasi free for X-ray interactions far from atomic resonances. However, the energy of the photons generated in NLCS at intensities reaching up to 4 x 1020 W/cm2 exhibit an anomalous red-shift that is in violation with the free-electron model. Here we investigate the underlying physics of X-ray nonlinear interactions at intensities on order of 1016 W/cm2. Specifically, we perform a systematic study of XSHG in diamond. While one phase-matching geometry has been measured in Shwartz et al.[4], we extend these studies to multiple Fourier components and with significantly higher statistics, which allows us to determine the second order nonlinear structure factor. We measure the efficiency, angular dependence, and contributions from different source terms of the process. We find good agreement of our measurements with the quasi-free electron model.
rate research
Read More
We describe a novel scheme of detecting rotational anisotropy second harmonic generation (RA-SHG) signals using a lock-in amplifier referenced to a fast scanning RA-SHG apparatus. The method directly measures the $n^{th}$ harmonics of the scanning frequency corresponding to SHG signal components of $C_n$ symmetry that appear in a Fourier series expansion of a general RA-SHG signal. GaAs was used as a test sample allowing comparison of point-by-point averaging with the lock-in based method. When divided by the $C_infty$ signal component, the lock-in detected data allowed for both self-referenced determination of ratios of $C_n$ components of up to 1 part in 10$^4$ and significantly more sensitive measurement of the relative amount of different $C_n$ components when compared with conventional methods.
In this letter we experimentally demonstrate second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612nm, using 3ps pump pulses having peak intensities of order of 10MW/cm2. We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.
A scheme for active second harmonics generation is suggested. The system comprises $N$ three-level atoms in ladder configuration, situated into resonant cavity. It is found that the system can lase in either superradiant or subradiant regime, depending on the number of atoms $N$. When N passes some critical value the transition from the super to subradiance occurs in a phase-transition-like manner. Stability study of the steady state supports this conclusion.
On the basis of the Edward-Kornfeld formulation, we study the effective susceptibility of secondharmonic generation (SHG) in colloidal crystals, which are made of graded metallodielectric nanoparticles with an intrinsic SHG susceptibility suspended in a host liquid. We find a large enhancement and redshift of SHG responses, which arises from the periodic structure, local field effects and gradation in the metallic cores. The optimization of the Ewald-Kornfeld formulation is also investigated.
Efficient frequency conversion techniques are crucial to the development of plasmonic metasurfaces for information processing and signal modulation. In principle, nanoscale electric-field confinement in nonlinear materials enables higher harmonic conversion efficiencies per unit volume than those attainable in bulk materials. Here we demonstrate efficient second-harmonic generation (SHG) in a serrated nanogap plasmonic geometry that generates steep electric field gradients on a dielectric metasurface. An ultrafast pump is used to control plasmon-induced electric fields in a thin-film material with inversion symmetry that, without plasmonic enhancement, does not exhibit an an even-order nonlinear optical response. The temporal evolution of the plasmonic near-field is characterized with ~100as resolution using a novel nonlinear interferometric technique. The ability to manipulate nonlinear signals in a metamaterial geometry as demonstrated here is indispensable both to understanding the ultrafast nonlinear response of nanoscale materials, and to producing active, optically reconfigurable plasmonic devices
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
