Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCoherent control of superradiance from nitrogen ions pumped with femtosecond pulses
158
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Singly ionized nitrogen molecules in ambient air pumped by near-infrared femtosecond laser give rise to superradiant emission. Here we demonstrate coherent control of this superradiance by injecting a pair of resonant seeding pulses inside the nitrogen gas plasma. Strong modulation of the 391.4 nm superradiance with a period of 1.3 fs is observed when the delay between the two seeding pulses are finely tuned, pinpointing the essential role of macroscopic coherence in this lasing process. Based on this time-resolved method, the complex temporal evolution of the macroscopic coherence between two involved energy levels has been experimentally revealed, which is found to last for around 10 picoseconds in the low gas pressure range. These observations provide a new level of control on the air lasing based on nitrogen ions, which can find potential applications in optical remote sensing.
rate research
Read More
Coherent control is an optical technique to manipulate quantum states of matter. The coherent control of 40-THz optical phonons in diamond was demonstrated by using a pair of sub-10-fs optical pulses. The optical phonons were detected via transient transmittance using a pump and probe protocol. The optical and phonon interferences were observed in the transient transmittance change and its behavior was well reproduced by quantum mechanical calculations with a simple model which consists of two electronic levels and shifted harmonic oscillators.
The ongoing development of intense high-harmonic generation (HHG) sources has recently enabled highly nonlinear ionization of atoms by the absorption of at least 10 extreme-ultraviolet (XUV) photons within a single atom [Senfftleben textit{et al.}, arXiv1911.01375]. Here we investigate the role that reshaping of the fundamental, few-cycle, near-infrared (NIR) driving laser within the 30-cm-long HHG Xe medium plays in the generation of the intense HHG pulses. Using an incident NIR intensity that is higher than what is required for phase-matched HHG, signatures of reshaping are found by measuring the NIR blueshift and the fluorescence from the HHG medium along the propagation axis. These results are well reproduced by numerical calculations that show temporal compression of the NIR pulses in the HHG medium. The simulations predict that after refocusing an XUV beam waist radius of 320 nm and a clean attosecond pulse train can be obtained in the focal plane, with an estimated XUV peak intensity of 9x10^15 W/cm^2. Our results show that XUV intensities that were previously only available at large-scale facilities can now be obtained using moderately powerful table-top light sources.
We present an analysis of two experimental approaches to controlling the directionality of molecular rotation with ultrashort laser pulses. The two methods are based on the molecular interaction with either a pair of pulses (a double kick scheme) or a longer pulse sequence (a chiral pulse train scheme). In both cases, rotational control is achieved by varying the polarization of and the time delay between the consecutive laser pulses. Using the technique of polarization sensitive resonance-enhanced multi-photon ionization, we show that both methods produce significant rotational directionality. We demonstrate that increasing the number of excitation pulses supplements the ability to control the sense of molecular rotation with quantum state selectivity, i.e. predominant excitation of a single rotational state. We also demonstrate the ability of both techniques to generate counter-rotation of molecular nuclear spin isomers (here, ortho- and para-nitrogen) and molecular isotopologues (here, 14N_2 and 15N_2).
Quantum effects, prevalent in the microscopic scale, generally elusive in macroscopic systems due to dissipation and decoherence. Quantum phenomena in large systems emerge only when particles are strongly correlated as in superconductors and superfluids. Cooperative interaction of correlated atoms with electromagnetic fields leads to superradiance, the enhanced quantum radiation phenomenon, exhibiting novel physics such as quantum Dicke phase and ultranarrow linewidth for optical clocks. Recent researches to imprint atomic correlation directly demonstrated controllable collective atom-field interactions. Here, we report cavity-mediated coherent single-atom superradiance. Single atoms with predefined correlation traverse a high-Q cavity one by one, emitting photons cooperatively with the atoms already gone through the cavity. Such collective behavior of time-separated atoms is mediated by the long-lived cavity field. As a result, a coherent field is generated in the steady state, whose intensity varies as the square of the number of traversing atoms during the cavity decay time, exhibiting more than ten-fold enhancement from noncollective cases. The correlation among single atoms is prepared with the aligned atomic phase achieved by nanometer-precision position control of atoms with a nanohole-array aperture. The present work deepens our understanding of the collective matter-light interaction and provides an advanced platform for phase-controlled atom-field interactions.
We discuss finite-difference time-domain simulations of femtosecond pulses interacting with silver nanowires and nanoparticles. We show how localized hot spots near the metal surfaces can be generated and controlled in a spatiotemporal manner. The control is made possible by chirping the pulses such that the effective frequency passes through surface plasmon resonances associated with different spatial regions of the nanostructure over the course of time. The response of such nanostructures to chirped pulses could provide a novel means of encoding or decoding optical signals.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
