122 research outputs found
Single-shot carrier-envelope-phase measurement in ambient air
The ability to measure and control the carrier envelope phase (CEP) of
few-cycle laser pulses is of paramount importance for both frequency metrology
and attosecond science. Here, we present a phase meter relying on the
CEP-dependent photocurrents induced by circularly polarized few-cycle pulses
focused between electrodes in ambient air. The new device facilitates compact
single-shot, CEP measurements under ambient conditions and promises CEP tagging
at repetition rates orders of magnitude higher than most conventional CEP
detection schemes as well as straightforward implementation at longer
wavelengths
Low temperature dipolar echo in amorphous dielectrics: Significance of relaxation and decoherence free two level systems
The nature of dielectric echoes in amorphous solids at low temperatures is
investigated. It is shown that at long delay times the echo amplitude is
determined by a small subset of two level systems (TLS) having negligible
relaxation and decoherence because of their weak coupling to phonons. The echo
decay can then be described approximately by power law time dependencies with
different powers at times longer and shorter than the typical TLS relaxation
time. The theory is applied to recent measurements of two and three pulse
dipolar echo in borosilicate glass BK7 and provides a perfect data fit in the
broad time and temperature ranges under the assumption that there exist two TLS
relaxation mechanisms due to TLS-phonons and TLS-TLS interaction. This
interpretation is consistent with the previous experimental and theoretical
investigations. Further experiments verifying the theory predictions are
suggested.Comment: 10 pages, 8 figure
A unified picture of aggregate formation in a model polymer semiconductor during solution processing
One grand challenge for printed organic electronics is the development of a knowledge platform that describes how polymer semiconductors assemble from solution, which requires a unified picture of the complex interplay of polymer solubility, mass transport, nucleation and, e.g., vitrification. One crucial aspect, thereby, is aggregate formation, i.e., the development of electronic coupling between adjacent chain segments. Here, it is shown that the critical aggregation temperatures in solution (no solvent evaporation allowed) and during film formation (solvent evaporation occurring) are excellent pointers to i) establish reliable criteria for polymer assembly into desired aggregates, and ii) advance mechanistic understanding of the overall polymer assembly. Indeed, important insights are provided on why aggregation occurs via a 1- or 2-step process depending on polymer solubility, deposition temperature and solvent evaporation rate; and the selection of deposition temperatures for specific scenarios (e.g., good vs bad solvent) is demystified. Collectively, it is demonstrated that relatively straightforward, concurrent in situ time-resolved absorbance and photoluminescence spectroscopies to monitor aggregate formation lead to highly useful and broadly applicable criteria for processing functional plastics. In turn, improved control over their properties and device performance can be obtained toward manufacturing sensors, energy-harvesting devices and, e.g., bioelectronics systems at high yield
The emergence of macroscopic currents in photoconductive sampling of optical fields
Photoconductive field sampling enables petahertz-domain optoelectronic applications that advance our understanding of light-matter interaction. Despite the growing importance of ultrafast photoconductive measurements, a rigorous model for connecting the microscopic electron dynamics to the macroscopic external signal is lacking. This has caused conflicting interpretations about the origin of macroscopic currents. Here, we present systematic experimental studies on the signal formation in gas-phase photoconductive sampling. Our theoretical model, based on the Ramo–Shockley-theorem, overcomes the previously introduced artificial separation into dipole and current contributions. Extensive numerical particle-in-cell-type simulations permit a quantitative comparison with experimental results and help to identify the roles of electron-neutral scattering and mean-field charge interactions. The results show that the heuristic models utilized so far are valid only in a limited range and are affected by macroscopic effects. Our approach can aid in the design of more sensitive and more efficient photoconductive devices
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