We theoretically show that two-photon coherent control yields electron photoemission from metal nanostructures that is localized in nanosize hot spots whose positions are controllable on a nanometer scale, in agreement with recent experiments. We propose to use silver V-shapes as tailored nanoantennas for which the position of the coherently controllable photoelectron emission hot spot can be deterministically predicted. We predict that the low-frequency, high-intensity (quasi-stationary) excitation of the photoemission leads to an exponentially high contrast of the coherent control.In various fields of nanoscience and nanotechnology, one of the key processes to achieve is controlled photoinduced injection of charges into nanoscopic regions of semiconductor or metal systems or vacuum. It is very important to perform this injection as an ultrafast process, on a femtosecond or subfemtosecond scale, and have a possibility to choose the injection nanosite dynamically with a nanometer-scale resolution. Such processes can be used, for instance, in sitespecific, time-resolved electron-excitation spectroscopy of molecules and nanoobjects; its technological applications are possible in superfast nano-optoelectronics to transfer signals from optical to electronic components. There are, however, major obstacles to implementation of such processes. One of them is that light cannot be focused to nanoscopic regions directly. Using the adiabatic transformation, it is possible to transfer the optical excitation energy and coherence to the nanoscale;1 however, such a concentration and the electron photoemission caused by it are static in space. Coherent control has been employed to dynamically change spectrum of photoelectrons emitted in a two-photon process from the Cu(111) surface. 2 We have proposed to use the coherent control to dynamically concentrate the optical excitation energy in space and time on the nanometer-femtosecond scale. 3,4 For nonlinear photoprocesses, such a concentration is possible and the time integral is coherently controllable. 3 This phenomenon has been later observed for two-photon electron emission from random nanostructured metal systems using two-pulse, interferometric coherent control in combination with electron microscopy. 5In this Letter, we pursue two related goals: (a) We show that the two-photon (interferometric) coherent control allows one to dynamically control electron emission from randomly rough surfaces, which is localized within a few nanometers; we also propose metal nanoantennas whose photoelectron emission is predictable, highly localized, and coherently controllable. (b) We predict that the photoelectron emission from metal nanostructures in the strong field (quasi-stationary) regime allows for coherent control with extremely high contrast, suitable for nanoelectronics applications.Consider a specific variant of the coherent control where a femtosecond excitation pulse consists of two identical laser subpulses with a controllable temporal delay τ between them, as shown in ...

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In this paper, we discuss how online AI stimulates epistemic ignorance. Early visions of online information search and retrieval processes proposed a utopian and empowering space for individuals. Today’s crisis paradoxically presents us with an unprecedented accumulation of new information and access to it, yet also the colonisation of this knowledge by those who seek to erode critical thought. By ‘epistemic ignorance’, we mean the condition which is systematically created by the patterns of mis- and disinformation that prevent knowledge seekers from gaining verified knowledge. We argue not only has the ‘knower’ or knowledge seeker become the ‘known’ (sometimes without knowing it), their ability ‘to know’ is also intentionally manipulated by dark patterns. Moreover, their ‘known’ status allows for their subtle indoctrination, and erosion of criticality. This makes the crisis an educational one. To illustrate, we consider epistemic mechanisms on Facebook pertaining to the early stage of the Covid-19 pandemic. We contend these ‘dark AI patterns’ intentionally aim for systemic indoctrination, and affective indoctrination, by engaging in the construction of epistemic ignorance. Our focus is on the political agenda; which is common in the wider discussion of indoctrination in education. Many educational philosophers have taken a critical interest in the power of education to indoctrinate. The formal educational space is an effective vehicle to do so – and now the informal education we receive through social media is as well. Through algorithms, we are taught to think a certain way.  This new crisis has not yet been considered an educational one, while in every moment, the coercive powers of online AI drive audiences towards greater uncritical acceptance of knowledge and information. Perhaps we can reverse the educational oppression with the introduction of ‘light patterns’.

FRIDAY MORNING / QELS 2002 / 259 QFB5 Fig. 1. Sample structure and cw PL at 300 K measured by He-Cd laser at 325 nm. T i m e In$) 2 4 6Tim e (nr) QFB5 Roam temperature TRPL measuremem using a TiSapphire laser The pump excitation energy was 3.14 eV (395 nm), below the bandgap of the InGaN reference layer and GaN buffer layer so electron-hole pairs were generated only in the SQW. Emission wavelength dependence on the decay time fork,-395 (3.14eV)with awavelengthwindowaf25nm.SolidlineindicatesPLfromInGaNsideand dotted lines is the PL from the silvered side. Fig. 2. IO0 H . O S W r m i g 2 . c 20 5 3 f n. 25 32 3 . En*roYCW -QFB5 Fig. 3. The Purcell enhancement factor, measured using cw PL (PL comparison) and TRPL (rate constant comparison).PL emission (450 nm) and fastest ( T~ = 4-5 ns) at the longest and shortest wavelengths measured (Fig. 2b). By contrast, the wealter PL intensity through the silver-coated surface exhibits a bi-exponential decay. The faster decay component is strongest near E,p (2.85 eV), is evident within 200 meV of $, and has a decay constant (r, -235 ps). This indicates that T, is a measure ofthe enhanced SE rate into the SP resonance at k,p, a process which OCEU~S T&, = 60 times faster (at 2.85 eV) than the decay into free space from the unsilvered side. In Fig. 3 the cw PL ratio demon-Strates q with a maximum of 35 centered at 2.97 eV compared to the TRPL ratio, measured at two positions 'P,'and 'Pi with slightly differing silver layerthicknesswithq = 36 (at2.83 eV) and92 (at 2.79 eV), respectively.The degree of enhancement increases with increasing film thickness and decreasing GaN cap layer thickness. Enhancement factors of almost 100 were indicated by dramatically accelerated TRPL decay at a frequency corresponding to the SP resonance.From a partial-differential eigenproblem, without use of dipole approximation, we show that the eigenmodes (surface plasmons) of disordered nanosystems (modeled as random planar composites) are not universally Anderson-localized, but can have properties of both localized and delocalized states simultaneously.' Their topology is determined by separate small-scale "hot spots" that are distributed and coherent over a length that may be comparable to the total si= of the system. Coherence lengths and oscillator strengths vary by orders of magnitude from mode to mode at nearby frequencies. The existence of dafk VI . luminous eigenmodes is established (the dark eigenmodes do not contribute to optical responses, and the luminous eigenmodes do) and attributed to the effect of charge-and parity-conservation laws. Possible applications are discussed. The theory is based on the spectral representation?The results for random planar nanostructured composites are illustrated in Fig. 1. They show that eigenmades with a similar gwmetry of local field intensities (delocalized in this case) may be eitherluminousordark [cf.(a)and(b)l.Thedistribution over the localization lengths L is very wide, from the minimum scale to the Size of the -~ e, =--~'