Abstract The interest in unipolar pulses in optics is related to the possibility of their efficient action on quantum objects. In this work, we study the interaction of a short rectangular unipolar pulse with a two-level resonant medium under conditions that the pulse duration is shorter than the relaxation times of the medium. It is paradoxical that the polarization and the population difference of the medium oscillate not at the Rabi frequency, but, rather, at a frequency that is proportional to the sum of the squared frequency of the resonant transition of the medium and the squared Rabi frequency of the pulse. This phenomenon is similar to the Stark effect, which consists of a shift of the transition frequencies of a medium in a constant external electric field. The possibility of generating radiation at frequencies that exceed the resonant transition frequency of the medium upon its excitation by a rectangular unipolar pulse is discussed.
Abstract The interest in unipolar pulses in optics is related to the possibility of their efficient action on quantum objects. In this work, we study the interaction of a short rectangular unipolar pulse with a two-level resonant medium under conditions that the pulse duration is shorter than the relaxation times of the medium. It is paradoxical that the polarization and the population difference of the medium oscillate not at the Rabi frequency, but, rather, at a frequency that is proportional to the sum of the squared frequency of the resonant transition of the medium and the squared Rabi frequency of the pulse. This phenomenon is similar to the Stark effect, which consists of a shift of the transition frequencies of a medium in a constant external electric field. The possibility of generating radiation at frequencies that exceed the resonant transition frequency of the medium upon its excitation by a rectangular unipolar pulse is discussed.
Abstract In the case of coherent interaction with a medium of extremely short light pulses (ESPs) having a carrier frequency and harmonic shape (when the pulse durations are shorter than the population relaxation times T1 and polarization relaxation time T2 of the medium), electromagnetically induced gratings (EMIGs) of the population difference, which have a pronounced harmonic dependence on the coordinates, may appear in it. These structures can occur when pulses do not overlap or overlap in the medium. Recently, the possibility of obtaining unipolar electromagnetic pulses in the optical and adjacent ranges of non-harmonic shape, for example, rectangular and triangular, with a duration less or comparable to the duration of the extremely-short pulse in this range, has attracted interest. In this work, using the numerical solution of the system of Maxwell–Bloch equations, we study EMIG formation by rectangular attosecond pulses in a two-level resonant medium. The possibility of inducing an EMIG of a non-harmonic shape in the form of light-induced channels microresonators (microcavities) with a size of the order of the wavelength of the resonant transition of the medium, whose parameters can be controlled, for example, by the amplitude of the incident pulses, is shown. It has been suggested that it is possible to create an EMIG of a predetermined non-harmonic shape only in the general case of using unipolar pulses.
In the case of coherent interaction with a medium of extremely short light pulses (ESPs) having a carrier frequency and harmonic shape (when the pulse durations are shorter than the population relaxation times T1 and polarization relaxation time T2 of the medium), electromagnetically induced gratings (EMIGs) of the population difference, which have a pronounced harmonic dependence on the coordinates, may appear in it. These structures can occur when pulses do not overlap or overlap in the medium. Recently, the possibility of obtaining unipolar electromagnetic pulses in the optical and adjacent ranges of non-harmonic shape, for example, rectangular and triangular, with a duration less or comparable to the duration of the extremely-short pulse in this range, has attracted interest. In this work, using the numerical solution of the system of Maxwell-Bloch equations, we study EMIG formation by rectangular attosecond pulses in a two-level resonant medium. The possibility of inducing an EMIG of a non-harmonic shape in the form of light-induced channels microresonators, (microcavities) with a size of the order of the wavelength of the resonant transition of the medium, whose parameters can be controlled, for example, by the amplitude of the incident pulses, is shown. It has been suggested that it is possible to create an EMIG of a predetermined non-harmonic shape only in the general case of using unipolar pulses. Keywords: attosecond pulses, unipolar pulses, rectangular pulses, electromagnetically induced gratings, polarization waves, light-induced microresonators.
In the case of coherent interaction with a medium of extremely short light pulses from a carrier of a harmonic form (when the pulse durations are shorter than the population relaxation times T_1 and polarization T_2 of the medium), electromagnetically induced gratings (EMIGs) of the population difference, which have a pronounced harmonic dependence on the coordinates, may appear in it. These structures can occur when pulses do not overlap at the same time or overlap in the medium. Recently, the possibility of obtaining unipolar electromagnetic pulses of the optical and adjacent ranges of non-harmonic shape, for example, rectangular and triangular, with a duration less than or comparable to the duration of the PCR in this range, has attracted interest. In this work, using the numerical solution of the system of Maxwell-Bloch equations, we study EMIG induced by rectangular attosecond pulses in a two-level resonant medium. The possibility of inducing an EMIG of a non-harmonic form in the form of light-induced channels, a kind of microresonators, with a size of the order of the wavelength of the resonant transition of the medium, whose parameters can be controlled, for example, by the amplitude of the incident pulses, is shown. It has been suggested that it is possible to create an EMIG of a predetermined non-harmonic form only in the general case of using unipolar pulses.
Unipolar light pulses with a non-zero electric area due to the unidirectional action on charged particles can be used for the ultrafast control of the properties of quantum systems. To control atomic properties in an efficient way, it is necessary to vary the temporal shape of the pulses used. This has led to the problem of obtaining pulses of an unusual shape, such as a rectangular one. A number of new phenomena, not possible with conventional multi-cycle pulses, were discovered by analyzing the interaction of such unipolar pulses with matter. These include the formation of dynamic microcavities at each resonant transition of a multilevel medium when such pulses collide with the medium. In this work, we compare the behavior of dynamic microcavities in a two-level and a three-level medium when unipolar pulses of unusual shape (rectangular) are collided with the medium. We do this on the basis of the numerical solution of the system for the density matrix of the medium and the wave equation for the electric field. Medium parameters correspond to atomic hydrogen. It is shown that for rectangular pulses in a three-level medium, the dynamics of the cavities can be very different from the two-level model, as opposed to pulses of other shapes (e.g. Gaussian shape). When the third level of the medium is taken into account, the self-induced transparency-like regime disappears. Differences in the dynamics of resonators in a three-level medium are revealed when the pulses behave like 2π pulses of self-induced transparency.
We theoretically demonstrate the possibility to tune the temporal waveform of optical unipolar pulses upon their coherent interaction with a multi-level resonant medium. This is achieved through the coherent control of the response of a multi-level resonant medium by means of half-cycle unipolar pulses. We show that despite the ultrabroad spectrum of half-cycle pulses one can efficiently steer the induced medium polarization through the proper choice of the parameters of the excitation pulses. As the result, producing of unipolar optical pulses of varying profile, like rectangular or triangular ones, from an extended layer of a multi-layer medium was obtained when excited by a pair of half-cycle pulses. Besides, we find out that the response of a multi-level medium for the amplitude of the driving pulses below a certain threshold can be quantitatively well approximated by the two-level model.
Abstract With the coherent interaction of a sequence of extremely short light pulses with a resonant medium (when the duration of the pulses and the delays between them are shorter than the relaxation times of the population difference T1 and polarization T2 of the medium), it is possible to create spatial electromagnetically induced gratings (EMIG) of polarization and population difference in the medium, as well as their ultrafast control. The dynamics of such gratings is of interest in connection with the possibility of ultrafast control over the properties of a medium at times of the order of the pulse duration and their influence on the stability of generation of extremely short pulses in a laser with a short linear cavity. In this paper, based on the numerical solution of the system of Maxwell-Bloch equations, an unusual and interesting possibility of the appearance of narrow and alternating sections in the medium is shown and studied in detail, in which harmonic polarization waves of the medium are formed, propagating in opposite directions relative to neighboring sections. This situation occurs when two extremely short attosecond pulses collide in a two-level resonant medium.