A physically unclonable function (PUF) is a multiple-input, multiple-output, large entropy physical system that is unreproducible due to its structural complexity A public physically unclonable function (PPUF) is a PUF that is created so that its simulation is feasible but requires very large time even when ample computational resources are available Using PPUFs, we have developed conceptually new secret key exchange and public key protocols that are resilient against physical and side channel attacks and do not employ unproven mathematical conjectures Judicious use of PPUF hardware sharing, parallelism, and provably correct partial simulation enables 1016 advantage of communicating parties over an attacker, requiring over 500 of years of computation even if the attacker uses all global computation resources

/pdf/hardware-based-public-key-cryptography-with-public-4c41h125m6.pdf

Hardware-Based Public-Key Cryptography with Public Physically Unclonable Functions

Springer Handbook of Lasers and Optics

Attosecond pulses are central to the investigation of valence- and core-electron dynamics on their natural timescales1–3. The reproducible generation and characterization of attosecond waveforms has been demonstrated so far only through the process of high-order harmonic generation4–7. Several methods for shaping attosecond waveforms have been proposed, including the use of metallic filters8,9, multilayer mirrors10 and manipulation of the driving field11. However, none of these approaches allows the flexible manipulation of the temporal characteristics of the attosecond waveforms, and they suffer from the low conversion efficiency of the high-order harmonic generation process. Free-electron lasers, by contrast, deliver femtosecond, extreme-ultraviolet and X-ray pulses with energies ranging from tens of microjoules to a few millijoules12,13. Recent experiments have shown that they can generate subfemtosecond spikes, but with temporal characteristics that change shot-to-shot14–16. Here we report reproducible generation of high-energy (microjoule level) attosecond waveforms using a seeded free-electron laser17. We demonstrate amplitude and phase manipulation of the harmonic components of an attosecond pulse train in combination with an approach for its temporal reconstruction. The results presented here open the way to performing attosecond time-resolved experiments with free-electron lasers. Generation of intense attosecond waveforms with independently controllable amplitude and phase is performed by using a seeded free-electron laser.

Attosecond pulse shaping using a seeded free-electron laser.

The long-standing scientific quest of real-time tracing electronic motion and dynamics in all states of matter has been remarkably benefited by the development of intense laser-based pulsed sources with a temporal resolution in the attosecond [1 attosecond = 10−18 s] time scale. Nowadays, attosecond pulses are routinely produced in laboratories by the synthesis of the frequency components of broadband coherent extreme ultraviolet (XUV) radiation generated by the interaction of matter with intense femtosecond (fs) pulses. Attosecond pulse metrology aims at the accurate and complete determination of the temporal and phase characteristics of attosecond pulses and is one of the most innovative challenges in the broad field of ultrashort pulse metrology. For more than two decades since coherent high-brilliance broadband XUV sources have become available, fascinating advances in attosecond pulse metrology have led to the development of remarkable techniques for pulse duration measurements as well as the complete reconstruction of those pulses. Nonetheless, new challenges born from diverse fields call upon for additional efforts and continuously innovative ideas in the field. In this perspective article, we follow the history of ultrashort pulse technology tracing attosecond pulse production and characterization approaches, focus on the operation principles of the most commonly used techniques in the region where they interact with matter, address their limitations, and discuss future prospects as well as endeavors of the field to encounter contemporary scientific progress.

/pdf/attosecond-pulse-metrology-5ff7orrqd1.pdf

Attosecond pulse metrology

A study of the spatial coherence of the high order harmonic radiation generated by the interaction of 45 fs Ti:sapphire laser beam with carbon (graphite) plasma plume has been carried out using Young's double slit interferometry. It is observed that the spatial coherence varies with harmonic order, laser focal spot size in plasma plume, and peaks at an optimal spot size. It is also observed that the spatial coherence is higher when the laser pulse is focused before the plasma plume than when focused after the plume, and it decreases with increase in the harmonic order. The optimum laser parameters and the focusing conditions to achieve good spatial coherence with high harmonic conversion have been identified, which is desirable for practical applications of the harmonic radiation.

Study of the spatial coherence of high order harmonic radiation generated from pre-formed plasma plumes

We use semiconductor (Si) and metallic (Al, Zr) transmission filters to shape, in amplitude and phase, high-order harmonics generated from the interaction of an intense titanium sapphire laser field with a pulsed neon gas target. Depending on the properties of the filter, the emitted attosecond pulses can be optimized in bandwidth and/or pulse length. We demonstrate the generation of attosecond pulses centered at energies from 50 to 80 eV, with bandwidths as large as 45 eV and with pulse durations compressed to 130 as.

Broadband attosecond pulse shaping.

We present experiments on the control over spectral amplitude and phase of attosecond pulses, using metallic and semiconductor thin-film dispersive filters. A pulse duration as short as 130 as is obtained.

Broadband attosecond pulse shaping

A step towards a successful implementation of time-resolved digital in-line holography with extreme ultraviolet (XUV) radiation is presented. Ultra-short XUV pulses are produced as high-order harmonics of a femtosecond laser and a Schwarzschild objective is used to focus harmonic radiation at 38 nm and to produce a strongly divergent reference beam for holographic recording. Experimental holograms of thin wires are recorded and the objects reconstructed. Descriptions of the simulation and reconstruction theory and algorithms are also given. Spatial resolution of a few hundreds of nanometers is potentially achievable, and the micrometer resolution range is demonstrated.

XUV digital in-line holography using high-order harmonics

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Broadband attosecond pulse shaping.

Broadband attosecond pulse shaping

XUV digital in-line holography using high-order harmonics