Bichromatic Radiation Research Articles

Floquet Engineering of a Diatomic Molecule through a Bichromatic Radiation Field.

We report on a theoretical study of a Cs2 molecule illuminated by two lasers and show how this can result in novel quantum dynamics. We reveal that these interactions facilitate the bypass of the non-crossing rule, forming light-induced conical intersections and modifiable avoided crossings. Our findings show how laser field orientation and strength, along with initial phase differences, can control molecular-state transitions, especially on the micromotion scale. We also extensively discuss how the interaction of radiation with matter gives rise to the emergence of potential energy surfaces of hybrids of radiation and molecular states. This research advances a technique for manipulating photoassociation processes in Cs2 molecules, offering potential new avenues in quantum control.

Электромагнитно-индуцированная прозрачность в ячейках конечных размеров с антирелаксационным покрытием стенок

In this paper, we propose an approach that makes it possible to obtain an analytical expression of the spectral dependence of the resonance of electromagnetically induced transparency detected by bichromatic radiation in a cell of finite size in the longitudinal direction of the laser beam. Specular and diffuse reflections of atoms from walls are considered. It was found that a significant difference between these types of reflections takes place only for cells of small longitudinal dimensions compared to the splitting wavelength of the ground state of atoms. A physical explanation is proposed for the difference between the Stokes and anti-Stokes scattering channels of probe radiation in terms of dressed states.

Silicon ablation in air by mono- and bichromatic laser pulses with wavelength 355 and 532 nm

Ablation of silicon sample in air under irradiance of single anddouble laser pulses with wavelengths 355 and 532 nm was studied by means ofoptical and scanning electron microscopy, raman spectroscopy, profilometryof laser craters as well as video registration of plasma's plume radiationin time. Dependence of specific sample's material removal on laser fluenceand time interval between coupled pulses of bichromatic laser irradiance wasestablished. Spallation of silicon was found in broad range of irradianceparameters and parameters of craters formed by ablation and spallation underthe action of bichromatic laser radiation were determined. Keywords: nanosecond laser ablation, specific mass removal, surface modification, laser plasma dynamics, crater formation, spallation\

Silicon Plasma Heating in Air under Combined Bichromatic Laser Radiation at Wavelengths of 355 and 532 nm

Silicon Plasma Heating in Air under Combined Bichromatic Laser Radiation at Wavelengths of 355 and 532 nm

Абляция кремния в воздухе моно- и бихроматическими импульсами лазерного излучения с длинами волн 355 и 532 nm

Ablation of silicon sample in air under irradiance of single and double laser pulses with wavelengths 355 and 532 nm was studied by means of optical and scanning electron microscopy, raman spectroscopy, profilometry of laser craters as well as video registration of plasma’s plume radiation in time. Dependence of specific sample’s material removal on laser fluence and time interval between coupled pulses of bichromatic laser irradiance was established. Spallation of silicon was found in broad range of irradiance parameters and parameters of craters formed by ablation and spallation under the action of bichromatic laser radiation were determined.

A detailed investigation of single-photon laser enabled Auger decay in neon

Single-photon laser enabled Auger decay (spLEAD) is an electronic de-excitation process which was recently predicted and observed in Ne. We have investigated it using bichromatic phase-locked free electron laser radiation and extensive angle-resolved photoelectron measurements, supported by a detailed theoretical model. We first used separately the fundamental wavelength resonant with the Ne+ 2s–2p transition, 46.17 nm, and its second harmonic, 23.08 nm, then their phase-locked bichromatic combination. In the latter case the phase difference between the two wavelengths was scanned, and interference effects were observed, confirming that the spLEAD process was occurring. The detailed theoretical model we developed qualitatively predicts all observations: branching ratios between the final Auger states, their amplitudes of oscillation as a function of phase, the phase lag between the oscillations of different final states, and partial cancellation of the oscillations under certain conditions.

Modeling the Dynamics of the Excitation of Two-Level Particles with Pulses of Bichromatic Irradiation

Mathematical modeling of the excitation dynamics of an isolated two-level particle under bichromatic irradiation is carried out on basis of solutions of the Schrodinger equation for the probability amplitudes of the states of the composite system of the particle and an interaction two-mode quantized radiation field, with the photons for each of which in a superposition state at the initial time. An analytical expression describing the change in the time of the population of the excited state of a particle in the adsorption of one of the irradiation photons in the simplest case when the irradiation is a sequence of identical pulses of a sinusoidal form is obtained. The obtained time dependence is compared with the time dependence of the diagonal matrix element of the statistical operator of the particle in the excited state found on the basis of the numerical solution of the system of the optical Bloch equations, with the corresponding irradiation described by the classical theory. Examples of significant differences in the type of these compared time dependences for a number of characteristic cases of irradiation are given.

Raman − Ramsey pulsed excitation of coherent population trapping resonances in a 87Rb cell with a buffer gas

We report the results of experimental investigation of the Raman – Ramsey method of pulsed excitation of coherent population trapping (CPT) resonances in a rubidium vapour cell filled with a mixture of Ar and Ne buffer gases. For the development of compact quantum microwave frequency standards, this method is an alternative to the pulsed optical pumping method recently implemented using the same rubidium cell. Both methods have advantages over the traditional double radio-optical resonance technique, the main of which is the substantial suppression of the light shift of the clock transition frequency, since the evolution of the coherence of atomic states forming the clock transition occurs in the absence of laser radiation in the cell. The narrow (110 – 240 Hz) Raman – Ramsey resonances are obtained using the scheme of pulsed excitation of CPT resonances on the D1 lines of the 87Rb atom with the same linear (lin||lin) polarisations of the bichromatic laser radiation components. The process of optimising the central fringe linewidth, its contrast, and the linewidth-to-contrast ratio is described. The magnetic dependence of the Raman – Ramsey line central fringe linewidth is experimentally investigated.

Selective detection of polarisation components of a coherent population trapping signal in hot alkali metal atoms

A mathematical model of the interaction of bichromatic laser radiation with alkali metal atoms in an optically dense gas cell at above room temperature is constructed. Within the framework of the model, complete hyperfine and Zeeman structures of alkali metal atom levels are considered, which allows the propagation of radiation polarisation along the cell and the effect of a constant magnetic field to be correctly taken into account. It is found that the selective detection of polarisation radiation components carries additional information in comparison with a signal of total intensity.

Feedback-controlled and digitally processed coherent population trapping resonance conversion in 87Rb vapour to high-contrast resonant peak

This work reports on the study of a new approach to achievement of high-contrast resonant signals from coherent population trapping (CPT) resonances in 87Rb vapour based on feedback control and real-time digital processing of several measured parameters. This method consists in stabilisation of the value of a function depending on several system parameters measured as the frequency difference of the bichromatic pump radiation is scanned through adjustment of the pumping radiation power with a feedback loop. The present work made use of two such parameters: the pumping radiation power incident on and exiting from the optical cell. Exploration of the proposed method has shown that stabilisation of a linear combination of these two parameters results in a resonant peak whose contrast exceeds that of regular CPT resonance by more than two orders of magnitude at relatively slow CPT resonance scan rates, (scanning frequency of the frequency difference of the bichromatic field ∼1 Hz). When dynamically exciting the CPT resonance (the scan frequency of the frequency difference of the bichromatic field equal to 2 kHz), the resonant peak contrast was enhanced by over an order of magnitude.

Signature of induced transparency in metals and conductors under bichromatic irradiation

The theory of electromagnetically induced transparency (EIT) in a nonlinear conductive medium, which utilizes the classical approach instead of the traditional quantum optics scheme, has been recently suggested. We present the results of the bichromatic parametric irradiation experiments which validate the EIT effect within the mid-infrared spectrum. The studied materials include a highly dispersive gold (Au) and a low dispersive semiconductor zinc telluride (ZnTe). When the irradiation parameters satisfy the requirements of the EIT theory, the effect was shown to be strongly pronounced in both Au and ZnTe despite the very different optical properties of these conductors. The predictions of the theory regarding the existence of the EIT effect are shown to be in agreement with the experiment.

Increase in the resolution of the method of surface nanostructuring by femtosecond-laser impact through a layer of colloidal microparticles

It is experimentally demonstrated that by converting a few percent of the fundamental frequency pulse energy into the second harmonic one can obtain surface structures using dielectric microspheres with the dimension of the order of the second harmonic wavelength. Structuring by means of the second harmonic solely requires a significantly greater energy density in the pulse than using bichromatic irradiation. It is impossible to obtain structures using only the fundamental frequency radiation pulses, because radiation at the fundamental frequency is not focused by the system of microspheres. Therefore, the use of bichromatic pulses allows an essential increase in the structure recording density. Theoretical calculations demonstrating the possibility of further improvement of the structure recording density by using non-spherical microlenses of a smaller size made of a material with a higher refractive index are presented.

High-contrast atomic dark resonances formed in a ladder system of rubidium atoms in submicron structures

It is shown that high-contrast resonance of electromagnetically induced transparency (EIT) in a ladder Ξ-system of 5S 1/2-5P 3/2-5D 5/2 levels can be formed in optical cells containing a column of rubidium vapor with thickness L in an interval of 100 nm ≤ L ≤ 780 nm. Using bichromatic laser radiation with certain parameters, an 83% contrast of the EIT resonance (or dark resonance, DR) has been achieved for a vapor column thickness of L = 780 nm. An important condition for the formation of high-contrast DR is that the frequency of the coupling laser radiation must be resonant with the frequency of the corresponding 5P 3/2-5D 5/2 transition (for the probe radiation frequency scanned over the 5S 1/2-5P 3/2 transition). It is also shown that a DR can be formed at a record small vapor column thickness of L ≈ 100 nm. Expressions that can be used to estimate the expected DR width at small L values are presented.

Propagation of the phase pulses of bichromatic radiation under the electromagnetically induced transparency conditions

We study the dynamics of the phase pulses of laser radiation with two resonant frequency components propagating in an atomic three-level Λ type medium under coherent population trapping. Using the density matrix adiabatic approach we show that the effect of a very large slowing down occurs not only for amplitude pulses, but also for phase pulses. The group velocity of phase pulses can be controlled by the amplitudes of resonant fields. The analytical solution describing the mutual influence of the phase modulation of one field component on another is obtained.

Dissipative dynamics of qubits driven by a bichromatic field in the dispersive regime

We study the coherent dynamics of relaxing qubits driven by a bichromatic radiation in the dispersive regime in the case when the detuning of the frequency ωrf of a longitudinal radio-frequency field from the Rabi frequency ω1 in a transverse microwave field is comparable in magnitude to ωrf and ω1. We analytically describe this regime beyond the rotating wave approximation and find that the dominant feature of the dynamics of qubits is the shift in the Rabi frequency caused by the dynamical Zeeman and Bloch–Siegert-like effects. These fundamental effects can be experimentally separated because, unlike the Bloch–Siegert effect, the dynamical Zeeman effect depends on the detuning sign. Our theoretical results are in good agreement with the experimental data obtained in pulse electron paramagnetic resonance for the E′1 centers in crystalline quartz.

Millimeter/submillimeter mixing based on the nonlinear plasmon response of two-dimensional electron systems

The nonlinear plasmon response of a two-dimensional electron system with an incorporated defect to monochromatic and bichromatic microwave radiation has been investigated. The operation of an electronic device (mixer) based on the plasmon response with a record operational speed has been demonstrated and analyzed. It has been found that the system response time is no more than τ = 25 ps. It has been shown that the nonlinear response of the system is caused by a new physical mechanism of nonlinearity induced by the presence of an inhomogeneity in the electron system.

Plasma mechanisms of pulsed terahertz radiation generation

We present the results on generating terahertz radiation in the plasma of an optical discharge arising in the atmosphere during the focusing of femtosecond laser radiation. Different generation schemes related to focusing of the optical radiation by spherical and axicon lenses, with a constant electric field imposed on the laser spark region, as well as with the use of bichromatic laser radiation, are studied. Directivity patterns and polarization distributions of the terahertz radiation are analyzed in detail for different generation techniques. Comparison with the experimental results obtained by other research groups is given. Possible nonlinear mechanisms of the terahertz radiation generation are discussed.

Pulsed EPR of P1 centers in synthetic diamond under bichromatic excitation conditions

The dynamics of the interaction of P1 centers in synthetic diamond with a bichromatic radiation, representing microwave (MW) and radio frequency (RF) fields in a configuration characteristic of the stationary EPR spectroscopy with modulated magnetic field, has been studied using the transient nutation technique. It is demonstrated that a thermobaric treatment of the crystal leads to an increase in the phase relaxation time of P1 centers. Additional increase in this relaxation time is observed under the conditions of a nutation resonance, where the RF field frequency is close to the effective Rabi frequency in the MW field. These data are taken into account in considering the inversion of the EPR lines of P1 centers that was recently discovered in the stationary EPR.

10.1007/s11448-008-3003-3

The dynamics of a two-level spin system dressed by bichromatic radiation is studied under the conditions of double resonance when the frequency of one (microwave) field is equal to the Larmor frequency of the spin system and the frequency of the other (radio-frequency) field ωrf is close to the Rabi frequency ω1 in a microwave field. It is shown theoretically that Rabi oscillations between dressed-spin states with the frequency ɛ are accompanied by higher-frequency oscillations at frequencies nωrf and nωrf ± ɛ, where n = 1, 2,.... The most intense among these are the signals corresponding to n = 1. The counter-rotating (antiresonance) components of the RF field give rise to a shift of the dressed-state energy, i.e., to a frequency shift similar to the Bloch-Siegert shift. In particular, this shift is manifested as the dependence of the Rabi-oscillation frequency ɛ on the sign of the detuning ω1 − ωrf from resonance. In the case of double resonance, the oscillation amplitude is asymmetric; i.e., the amplitude at the sum frequency ωrf + ɛ increases, while the amplitude at the difference frequency ωrf − ɛ decreases. The predicted effects are confirmed by observations of the nutation signals of the electron paramagnetic resonance (EPR) of E′1 centers in quartz and should be taken into account to realize qubits with a low Rabi frequency in solids.

The effect of phase noise of bichromatic radiation upon resonances of coherent population trapping

We consider the effect of the noise difference phase of a bichromatic field upon coherent population trapping resonances in the simplest three-level system in Λ configuration. The quasi-stationary solution of Bloch optical equations, which was found with some assumptions, shows that the presence of exciting short-correlated fluctuations of the phase of radiation reduces the contrast of the resonance line without affecting its spectral width. For the Gaussian phase noise the contrast suppression factor is χ = exp[−ϕrms2], where ϕrms2 is phase dispersion. The experimental results obtained earlier by our group are analyzed.