Biharmonic Pumping Research Articles

Coherent Stokes and anti-Stokes high-order components generation by biharmonic pumping via stimulated low-frequency Raman scattering.

In this Letter, we report on experimental effective coherent multiple Stokes and anti-Stokes high-order components generation by Stokes pulse injection at the process of stimulated low-frequency Raman scattering. This process can be used for effective generation the tunable spectral comb consisting of several equidistant spectral lines separated by a constant frequency spacing of several GHz.

Features of the Magnetic Resonance of an Alkali Metal upon Biharmonic Pumping

The dynamics of spin projections of the electron shell of an alkali metal on the coordinate axis is considered in the electron paramagnetic resonance scheme with continuous pumping by biharmonic circularly polarized laser radiation. The working region is a cell with alkali vapor metal vapors and a buffer gas at a high concentration at temperature 60°C. It was found that the use of biharmonic pumping causes not only the expected electron-spin precession, but also pulsations of the electron-spin projection on the axis along which the magnetic field is directed. The frequency of these pulsations depends on the nuclear angular momentum of alkali metal atoms. In the case of the transverse electron magnetic resonance, this effect is absent.

Parametric Raman crystalline anti-Stokes laser at 503 nm with collinear beam interaction at tangential phase matching

Stimulated-Raman-scattering in crystals can be used for the single-pass frequency-conversion to the Stokes-shifted wavelengths. The anti-Stokes shift can also be achieved but the phase-matching condition has to be fulfilled because of the parametric four-wave mixing process. To widen the angular-tolerance of four-wave mixing and to obtain high-conversion-efficiency into the anti-Stokes, we developed a new scheme of the parametric Raman anti-Stokes laser at 503 nm with phase-matched collinear beam interaction of orthogonally-polarized Raman components in calcite oriented at the phase-matched angle under 532 nm 20 ps laser excitation. The excitation laser beam was split into two orthogonally-polarized components entering the calcite at the certain incidence angles to fulfill the nearly collinear phase-matching and also to compensate walk-off of extraordinary waves for collinear beam interaction. The phase matching of parametric Raman interaction is tangential and insensitive to the angular mismatch if the Poynting vectors of the biharmonic pump and parametrically generated (anti-Stokes) waves are collinear. For the first time it allows to achieve experimentally the highest conversion efficiency into the anti-Stokes wave (503 nm) up to 30% from the probe wave and up to 3.5% from both pump and probe waves in the single-pass picosecond parametric calcite Raman laser. The highest anti-Stokes pulse energy was 1.4 $$\upmu$$ J.

Measurements of the nonlinear acoustic parameter of sea water via a device using reflected pulses

A method for measuring the nonlinear acoustic parameter of sea water and a device in the form of an immersed sonde are described. The method is based on the principle of registration of waves at the difference frequencies in water at consecutive reflections of high-frequency biharmonic acoustic pumping waves between the walls of a measuring cell. Some results obtained during vertical sounding of the upper layer of the sea to a depth of 100 m are presented.

All-optical control of optical frequency combs via quantum interference effects in a single-emitter-microcavity system

Recent demonstrations of cavity quantum electrodynamics (QED) with a single quantum emitter coupled to an optical microcavity have shown the great potential of this system for engineering the light-matter interaction and developing a wide range of robust quantum devices. Here, we study the creation and all-optical control of optical frequency combs (OFCs) in photon emission from a single-quantum-emitter-microcavity QED system driven with a biharmonic pump light in the presence of a classical control light. We find that, when the strengths and phases of the applied control light are appropriately tuned, enhanced OFC generation can occur by using the parameters of currently existing QED systems. The interference between the biharmonic pump light, which is used to drive the cavity mode, and the light scattered by the two-level emitter into the cavity mode due to the second control light are responsible for the enhancement or suppression of OFCs. We further analyze in detail the influences of the other system parameters including the emitter-cavity coupling strength, the incident pump power, and all kinds of relative frequency detunings on all-optical generation of OFCs. In addition to numerical simulations demonstrating this controlled OFC effect, a complete physical explanation of the underlying mechanism is presented. The presented mechanism can be employed for tailoring and controlling OFCs in a cavity QED architecture.

Asymmetric frequency conversion in nonlinear systems driven by a biharmonic pump.

A novel mechanism of asymmetric frequency conversion is investigated in nonlinear dispersive devices driven parametrically with a biharmonic pump. When the relative phase between the first and second harmonics combined in a two-tone pump is appropriately tuned, nonreciprocal frequency conversion, either upward or downward, can occur. Full directionality and efficiency of the conversion process is possible, provided that the distribution of pump power over the harmonics is set correctly. While this asymmetric conversion effect is generic, we describe its practical realization in a model system consisting of a current-biased, resistively shunted Josephson junction. Here, the multiharmonic Josephson oscillations, generated internally from the static current bias, provide the pump drive.

Interference of biphotons upon parametric down-conversion in the field of biharmonic pumping

We report theoretical investigation of interference of biphotons emitted upon type-II collinear parametric down-conversion in the case of biharmonic pumping. Interference occurs when an optical or electronic shutter is used as an amplitude modulator in the experimental scheme. The phase of the interference is shown to depend on the time interval between the instant the shutter is opened and the instant corresponding to the maximum pump intensity. The main parameter affecting the visibility of the interference pattern is a time interval during which the shutter is open.

Experimental observation of stimulated low-frequency Raman scattering in water suspensions of silver and gold nanoparticles

In this Letter we report on experimental observation of stimulated low-frequency Raman scattering (SLFRS) in gold and silver nanoparticle suspensions excited by 20 ns ruby laser pulses, SLFRS propagated in forward and backward directions with a maximum conversion efficiency up to 20%. Frequency shift for silver nanoparticle suspension was found to be 0.33 THz and for gold nanoparticle suspension 0.435 THz. This type of stimulated scattering of light can be used as an effective source of biharmonic pumping for solving a large number of practical tasks.

Stimulated low-frequency Raman scattering in nanostructures

A new type of stimulated scattering of light (stimulated low-frequency Raman scattering (SLFRS)) is found. SLFRS appears as a result of interaction of laser pulses with acoustic vibrations of structural elements of nanostructured materials. SLFRS is shown to arise in materials with different compositions and different degrees of morphology, both ordered and random. Frequency shifts of SLFRS components are measured. A number of practical applications of the effect are proposed, in particular, biharmonic pumping with the help of SLFRS.

Discrete dispersion of optical pulses on nonlinear-induced moving lattice

A theory of the interaction of an optical pulse with a concurrently moving lattice created in a nonlinear medium by a biharmonic pump wave is presented. Regimes for the partitioning of a solitary signal into subpulses, trapping a pulsed signal into a parametric soliton, and eliminating the lattice dispersion of pulses with a certain velocity are found.

Spectral and temperature features of coherent picosecond nonlinear response of HTSCs at low excitation levels

It is shown that for the appropriate choice of the spectral measurement range (the choice of the coincidence point for the pumping component frequencies in the methods of biharmonic pumping and degenerate four-photon spectroscopy), the spectral and temperature features of the picosecond nonlinear response of high-temperature super-conductors (HTSCs) caused by interband transitions in the electronic spectrum with a metastable energy gap are stable with respect to the excitation level. The character of these features is determined by the resonance component of the total nonlinear response, which is formed at initial HTSC temperatures below the phase transition point (when the energy gap appears in the electronic spectrum).

Effect of laser pumping power on the SRS-CARS signal in compressed hydrogen

In the context of developing the diagnostics of hydrogen in gas mixtures by means of coherent anti-Stokes Raman scattering (CARS) in combination with biharmonic laser pumping by means of stimulated Raman scattering (SRS), the effect of laser pumping power on the SRS-CARS signal in compressed hydrogen has been studied. It is established that an increase in the pumping power at the input of the SRS generator leads to a shift of the CARS signal intensity maximum measured as a function of the gas pressure in the cell. This behavior is probably explained by changes in the positions of energy levels, which are caused by a significant modification of populations in the SRS process at high laser pumping powers.

Asymmetry of the Stokes and anti-Stokes components of the nonlinear response of high-temperature superconductors in the method of picosecond biharmonic pumping

It is shown in the model of the nonlinear response of high-temperature superconductors (HTSCs) caused by interband transitions in the electronic spectrum with a metastable energy gap that the Stokes and anti-Stokes components of the HTSC response to picosecond biharmonic pumping are asymmetric, and for the excitation-pulse frequency detuning exceeding 100 cm-1, the efficiency of self-diffraction in the directions corresponding to these two components is different.

Using biharmonic laser pumping for preparation of pure and entangled multiexciton states in clusters of resonantly interacting fluorescent centres

Use of a biharmonic laser pumping for preparation of pure and entangled multiexciton states in dimers and tetramers of resonantly interacting fluorescent particles is analysed. Special emphasis is given to the preparation of all possible pure exciton states and their maximally entangled Bell states. The general results are illustrated using as an example the pair and quartet centres of neodymium ions in calcium fluoride ( M- and N-centres), where all necessary experimental information concerning the interactions and decoherence is available, and experimental preparation of Bell vacuum–single exciton and vacuum–biexciton states has been recently demonstrated. These results can be easily rescaled for the cases of quantum dots and dye molecules. Numerical results are compared with the analytical results obtained for a particular case of the biharmonic excitation of dimers. Excellent agreement between these approaches is demonstrated.

Determination of the composition of mixtures of organic liquids by CARS spectroscopy

Two methods of realization of coherent anti-Stokes Raman scattering (CARS) spectroscopy of organic liquids are described: with a tunable dye laser and by means of biharmonic laser pumping based on stimulated Raman scattering. The second method is applied to liquids for the first time. The possibilities of the two methods are compared. CARS spectroscopy is applied for the first time to the analysis of a mixture of two organic liquids.

Quantum control of exciton states in clusters of resonantly interacting fluorescent particles using biharmonic laser pumping

Reference LPMV-ARTICLE-2006-001doi:10.1103/PhysRevB.74.165329View record in Web of Science Record created on 2007-06-20, modified on 2017-12-03

Features of the nonlinear response of high-temperature superconductors in coherent picosecond four-photon spectroscopy with high excitation level

Assuming that the nonlinear response of high-temperature superconductors is caused by interband transitions in the electronic spectrum with a metastable energy gap, a model describing the results of experiments performed by picosecond coherent four-photon spectroscopy with a high excitation level is developed. It is shown that a jump in the dependence of the self-diffraction efficiency on the initial temperature of a sample should be observed in the vicinity of the point of superconducting phase transition. It is found that upon biharmonic pump — probing, the energy gap in the electronic spectrum can be detected by a specific two-photon resonance.

A Laser-Based Apparatus for Estimating the Hydrogen Diffusion Constant in Gas Mixtures

A laser-based apparatus for determining the hydrogen diffusion constant in gas mixtures is described. The main units of the apparatus are a diffusion chamber and a computer-based laser system for the selective diagnostics of hydrogen in gas mixtures by coherent anti-Stokes Raman scattering (CARS) in combination with biharmonic pumping based on stimulated Raman scattering. The diffusion constant is estimated by approximating the experimental data that describe changes in the hydrogen concentration with time at a fixed point in the diffusion chamber and comparing them to the exact solution to the diffusion equation for the chosen one-dimensional experimental geometry.

Interference of coherently scattered signals in the laser SRS-CARS monitoring of hydrogen concentration in gas mixtures

The possibility of measuring the hydrogen impurity concentration in dense gas mixtures by coherent anti-Stokes Raman scattering (CARS) is studied. In this technique, biharmonic laser pumping based on stimulated Raman scattering (SRS) in compressed hydrogen is used. Because of the interference between the coherent scattering components from buffer gas molecules and molecules of the impurity to be detected, the signal recorded may depend on the hydrogen concentration by a parabolic law, which has a minimum and makes the results uncertain. It is shown that this uncertainty can be removed if the frequency of the biharmonic laser pump, which is produced by the SRS oscillator, somewhat differs from the frequency of molecular oscillations of hydrogen in the test mixture. A sensitivity of 5 ppm is obtained as applied to the hydrogen-air mixture under normal pressure. The coefficients of the nonresonance cubic hyperpolarizability of molecules and atoms are measured relative to nitrogen in a number of gas media.

Nonlinear susceptibility interference in laser SRS-CARS diagnostics of hydrogen in gas mixtures

We have studied the possibility to measure small hydrogen concentrations in dense gas mixtures by method of coherent anti-Stokes Raman scattering (CARS) in combination with biharmonic laser pumping by means of stimulated Raman scattering (SRS). It was found that the interference of nonlinear susceptibilities of a buffer gas and hydrogen can lead to a parabolic dependence of the signal intensity on the hydrogen concentration, which makes the results of analyses uncertain. The ambiguity can be eliminated by selecting an appropriate composition and pressure of the gas mixture in the cell of the SRS generator of biharmonic laser pumping. Using this approach, hydrogen in air at atmospheric pressure can be detected by the laser SRS-CARS technique on a level of 5 ppm.