Indicator.Ru: Unusual rectangular and triangular light pulses produced
Russian scientists have proposed a way to receive light pulses of unusual shapes: rectangular, triangular, and trapezoidal ones. Their use will make it possible to speed up several hundred-fold processing and transmission of data in a variety of optical devices, including quantum devices.
Electromagnetic waves can be divided into three main ranges depending on their length: infrared, ultraviolet and visible spectrum. The short pulses of radiation generated in these bands have one thing in common: they all have a carrier frequency belonging to the mentioned spectrum bands. At the carrier frequency, the electric field strength periodically and many times changes its direction according to the harmonic law.
The findings of the research supported by a grant from the Presidential Programme of the Russian Science Foundation are published in the journal Physical Review A.
Physicists from St Petersburg University (St Petersburg) and Ioffe Institute of the Russian Academy of Sciences (St Petersburg) have proposed how to create light pulses in which there is no carrier frequency, leaving only one oscillation, in which the electric field strength does not change direction. The method is based on using a non-linear medium with non-uniform characteristics, which is excited, and then this excitation is deactivated by a second pulse.
‘We have proposed a new way of producing unipolar pulses with an unusual shape, such as rectangular or triangular ones. Previously, such a task was considered unsolvable or at least extremely difficult. However, if pulse sources of a given shape are created, it will help develop optical devices capable of processing and transmitting information hundreds or thousands of times faster than the electronic circuits that are currently in use,’ said Rostislav Arkhipov, Principal Investigator of the project supported by the grant from the Russian Science Foundation, Candidate of Physics and Mathematics and Leading Research Associate at the Faculty of Physics of St Petersburg University.
The production of such pulses, the duration of which is extremely short, will make it possible to create superfast optical analogues of radioelectronic circuits capable of processing and transmitting information hundreds or thousands of times faster. The reason for the sharp increase in information capacity of pulses is their unipolarity. This means that a pulse does not change direction, there is no carrier, and therefore the bandwidth, which extends from zero to, for example, the visible spectrum, increases sharply. The information capacity of a signal includes all frequency ranges from radio and microwave to optical ones. Accordingly, having a source of such radiation can only be used to organise radio broadcasts, light shows and much more.
‘We have also investigated the excitation and ionisation of quantum systems when exposed to extremely short and unipolar pulses of light when their duration is shorter than the orbital period of an electron in an atom. Due to their unidirectional effect, such pulses can excite them faster and more effectively than conventional bipolar long pulses,’ added Nikolay Rozanov, Member of the Russian Academy of Sciences and Chief Research Associate at Ioffe Institute.
When unipolar pulses of such short duration are applied to microobjects, traditional theories become inapplicable. In this case, as the results of conducted investigations showed, the leading role is played by the electrical area of the active pulse: it is defined as the integral of the electric field strength over time in a given point of space. For conventional multi-cycle pulses, which are now produced in laser systems, the electrical area is always close to zero.
‘In order to assess the degree of effectiveness of such extremely short pulses on various quantum systems, we have introduced a new physical quantity − the atomic area measure. As our research has shown, the excitation and ionisation probabilities of atomic systems are determined by the ratio of the electrical area of the pulse to its atomic measure, rather than the pulse energy or its amplitude,’ added Nikolay Rozanov.