Harmonic Generation In Plasma Research Articles

Plasma harmonic generation for highly efficient Breit-Wheeler pair creation

Observation of efficient Breit-Wheeler electron-positron pair creation is one of the main goals for modern-day strong laser-particle experiments. We propose exploring this process by colliding plasma-generated harmonics, from currently available laser pulses, with a beam of GeV photons. We show that the creation yield is enhanced for more than one order of magnitude, compared with the yield obtained without high-harmonic generation. The robustness of the yield enhancement is demonstrated by considering multiple interaction parameters and the potential photon source for the upcoming experiments. Moreover, we show that due to the evident field asymmetry of the plasma-generated harmonics, the averaged spin-polarization of the created pairs could be as high as 62%.

High-Order Harmonics Generation in Selenium-Containing Plasmas

The studies of the high-order harmonics generated in Se-containing plasmas are reported. The ablation of selenium in a vacuum allowed for the formation of a plasma demonstrating high-order harmonics generation and resonance enhancement of the harmonic at the shortest wavelength reported so far (λ ≈ 22.9 nm, Eph ≈ 54.14 eV). This harmonic corresponds to the 35th order of the 800-nm-class lasers. The influence of the presence of selenium in the molecular state (ZnSe and HgSe) on the suppression of the resonance effect during harmonics generation in plasma is studied. The enhanced 35th harmonic was analyzed by different methods of plasma formation using nanosecond, picosecond, and femtosecond pulses. The enhancement factor of the resonance-enhanced harmonic was measured to be 32× compared with the neighboring lower-order harmonics in the case of the picosecond-pulses-induced Se plasma. The role of the strong ionic transition of Se in the region of 22.7 nm in the observation of the resonance-induced enhancement of a single harmonic is discussed.

Three-step model for third-harmonic generation in air by nanosecond lasers

Understanding the phenomena involved in harmonic generation in plasmas by high-power pulsed lasers is a paramount task for developing new techniques for generation of coherent radiation in ultrashort bursts. Although first experiments on harmonic generation involved nanosecond lasers and inspired further interest in the subject, numerical simulations on harmonic generation are currently mainly oriented toward ultrashort fs lasers. This paper presents a combined theoretical–experimental approach to the generation mechanisms and the properties of third-harmonic (TH) radiation generated by infrared nanosecond laser pulses in air-breakdown plasma. The paper indicates that, at the microscopic level, the generation of TH can be described by a three-step model, which involves breakdown of nitrogen molecules in the air. First, the nitrogen molecules undergo cascade-impact ionization; then, the ionized molecules are quasi-resonantly excited through three-photon absorption; in the third step, the nitrogen molecules de-excite to the fundamental level with associated emission of TH radiation. At the macroscopic level, the three-step model is implemented considering that the breakdown plasma is a conductive nonlinear medium whose third-order susceptibility and complex conductivity depend upon the cubic root of the driving laser intensity. The 2D numerical simulations performed in the frame of this model are in good agreement with the experimental data in terms of TH generation efficiency, collimation, and polarization of TH radiation, indicating the validity of the theoretical model presented here. The model enables realistic calculations with affordable computing power for prediction and control of the TH generation process driven by nanosecond laser pulses. The results are important from the fundamental and practical points of view, thus providing an efficient tool for prediction of nonlinear optical phenomena in laser-produced plasmas and for noncontact diagnosis of harmonic-generating plasmas.

Hermite-cosh-Gaussian laser-induced third harmonic generation in plasma

Present work focuses on Hermite-cosh-Gaussian (HchG) laser-induced third harmonic generation (THG) in plasma on account of self-focusing. HchG laser beam gets self-focused due to ponderomotive force while propagating in plasma. Interaction of intense laser pulse results ponderomotive force on electrons and induce density perturbation that produces density oscillations at second harmonic frequency. Induced density perturbation beats with quiver velocity of electrons at laser frequency to produce a third harmonic nonlinear current. Application of wiggler magnetic field satisfies the phase matching condition which results resonant THG. Significant enhancement in the efficiency of THG is observed by using HchG laser profile for mode index m = 2. Small variation in decentered parameter also affects the THG efficiency which shows the sensitivity of decentered parameter.

Features of the Second Harmonic Generation in CTA Target Plasma

The results of experiments on the study of the second harmonic generation in plasma of low-density cellulose triacetate targets are presented. Targets were irradiated using a neodymium glass laser at the nanosecond fundamental frequency. The data on the time sweep of the second harmonic generated in plasma are obtained. The features of the spectral and time distributions of the second harmonic radiation are discovered: with increasing the density, a maximum appears in the spectrum, and two maxima appear in the time dependence of the intensity.

Third harmonic generation of a relativistic self-focusing laser in plasma in the presence of wiggler magnetic field

Under the influence of relativistic self-focusing the phenomenon of third harmonic generation in plasma has been investigated. When a highly intense Gaussian laser penetrates through plasma channel it gets self-focused because of relativistic nonlinearity. Third harmonic pulse is produced as the result of beating ponderomotive force-induced density oscillations of second order with the quiver velocity of electron at the fundamental frequency. Further, it is noticed that both the magnetic field and the relativistic mass effect contribute for nonlinear dielectric response of plasma and hence, produce plasma channel because of influence of relativistic self-focusing. Enhancement in the intensity of the third harmonic generation is observed on account of relativistic self-focusing of fundamental pulse in the presence of wiggler magnetic field. Higher efficiency of third harmonic is reported in the region where self-focusing dominates and wiggler magnetic field provides the required phase matching condition.

Strong third-order optical nonlinearities of Ag nanoparticles synthesized by laser ablation of bulk silver in water and air

We demonstrate the correlation between strong nonlinear optical response of silver nanoparticles (Ag NPs) out of plasmon resonance and efficient third harmonic generation in the plasmas containing Ag NPs. The dynamics of nonlinear optical response of the 8 nm and 50 nm Ag NPs prepared by laser ablation of bulk silver in deionized water using 6 ns, 200 ps, and 60 fs laser pulses is systematically analyzed. Their optical limiting properties are studied at the wavelengths of 800 and 355 nm, using femtosecond and nanosecond laser pulses. Nonlinear absorption coefficient of 8 nm Ag NPs at the wavelength of 1064 nm was measured to be as high as 3 × 10−5 cm W−1. Nonlinear refraction shows the change of sign with variation of the wavelength and duration of probe laser pulses. The theoretical calculation of silver ablation shows the formation of a few nanometer sized particles. We also analyze third harmonic generation in the laser-produced plasmas containing Ag NPs and attribute the enhancement of this process to the influence of small silver clusters. The conversion efficiency of 800 nm towards the third harmonic was measured to be 4 × 10−3, which was a few times larger compared with similar process in air.

Exponential density transition-based enhanced second harmonic generation in plasma

AbstractEnhanced harmonic generation of second order based on exponential density ramp in plasma has been noticed. It is well known that self-focusing of pump laser induces a transverse intensity gradient, which gives rise to the plasma wave at the pump frequency. Highly intense Gaussian laser with exponential density ramp profile generates a second harmonic pulse in plasma. It is noticed that the amplitude of second-harmonic pulse varies periodically with the distance and reaches its peak value in the focal region. Further, it is found that exponential plasma density ramp is useful for stronger self-focusing, which lead to rise second harmonic generation (SHG). Wiggler magnetic field provides the additional angular momentum required for second harmonic photon and aids in growing of resonant process. One may clearly see that exponential plasma density ramp imparts a major role in enhancing the SHG in plasma. Further, the combined effect of exponential density ramp and wiggler magnetic field boosts the SHG in plasma.

Influence of density ripple on pulse slippage of third harmonic generation in plasma

Influence of density ripple on pulse slippage of third harmonic generation has been investigated. When highly intense short range laser pulse incident on plasma, it imparts oscillatory velocity to electrons and exert a ponderomotive force at twice the frequency of incident laser beam. It induces oscillatory velocity at second harmonic frequency 2ω which further couples with density ripple resulting in density oscillations at 2ω. Density oscillations at 2ω, couple with the oscillatory velocity at ω, to produce non-linear current density at 3ω which drives the third harmonic generation. In order to provide phase matching condition between fundamental and third harmonic pulses, density ripple in plasma is introduced which offers the required momentum to the third harmonic photon to make the process resonant. At resonance, amplitude of the third harmonic pulse is found to be maximum for optimized values of density ripple factor. It is observed that the peak value of third harmonic pulse shifted towards higher value of normalized distance z' for higher values of normalized time t'. It is also seen that on account of the group velocity mismatch between pump and third harmonic pulses, the third harmonic pulse slips out of the domain of pump pulse.

Two Methods of Amplification of Coherent Extreme Ultraviolet Radiation During Harmonic Generation in Plasmas

Different recently revealed approaches of harmonic enhancement in plasmas are reviewed. The 4-step analytical model of resonant enhancement of high-order harmonic generation is extended to the systems possessing resonant transitions of inner-shell electrons. Role of inelastic scattering is discussed by simulation of excited state’s population dynamics. The enhancement of harmonics in the In plasma using different pumps is analyzed to prove the concept. We also discuss the plasma emission and harmonic generation spectra in the case of resonance enhancement of single harmonic using various laser-produced plasmas. The analysis of these spectra showed that the enhancement of harmonics depended on the oscillator strengths of the nearby ionic transitions rather than the plasma emission transitions. Finally, we review some recent experimental studies of the phase-matching of high-order harmonic generation in multi-jet plasmas.

Resonant second harmonic generation in plasma under exponential density ramp profile

Resonant second harmonic generation of a relativistic self-focused laser beam in plasma under exponential density ramp profile is investigated. It has been found that the self-focusing of Gaussian laser beam becomes stronger in plasma with exponential density ramp profile hence, leads to enhance the resonant second harmonic generation. The periodic variation of the normalized second-harmonic amplitude with normalized distance has been analyzed for different laser and plasma parameters. Therefore, enhanced second harmonic generation on account of relativistic self-focusing of fundamental laser beam in plasma under plasma density transition is observed. One may notice that exponential density ramp plays an important role in making the self-focusing stronger which in turn enhances the second harmonic generation in plasma.

Two methods of amplification of coherent extreme ultraviolet radiation during harmonic generation in plasmas-=SUP=-*-=/SUP=-

Two methods of amplification of coherent extreme ultraviolet radiation during harmonic generation in plasmas-=SUP=-*-=/SUP=-

Resonance processes during harmonic generation in plasmas using mid-infrared radiation

A few recently introduced approaches of the high-order harmonic generation in laser-produced plasmas are reviewed. We show how the tuning of odd and even high-order harmonics of ultrashort pulses along the strong resonance of laser-produced indium plasma using optical parametric amplifier of white-light continuum radiation (1250−1400 nm) allows observation of different harmonics enhanced in the vicinity of the transition of In II ions possessing high oscillator strength. We discuss various peculiarities and discuss the theoretical model of the phenomenon of tunable harmonics enhancement in the region of 62 nm using indium plasma. With the theoretical analysis, we present the approach allowing reproduce the experimental observations and characterize the dynamics of the resonant harmonic emissions. We also discuss the resonance enhancement of harmonics using mid-infrared radiation in the tin, chromium, and antimony plasmas and show the calculations of this process.

Resonance Processes During Harmonic Generation in Plasmas Using Mid-Infrared Radiation, "Оптика и спектроскопия"

Resonance Processes During Harmonic Generation in Plasmas Using Mid-Infrared Radiation, "Оптика и спектроскопия"

Enhanced resonant second harmonic generation in plasma based on density transition

Abstract Resonant second harmonic generation of a relativistic self-focusing laser in plasma with density ramp profile has been investigated. A high intense Gaussian laser beam generates resonant second harmonic beam in plasma with density ramp profile. The second harmonic undergoes periodic focusing in the plasma channel created by the fundamental wave. The normalized second harmonic amplitude varies periodically with distance and attains maximum value in the focal region. Enhancement in the second harmonic amplitude on account of relativistic self-focusing of laser based on plasma density transition is seen. Plasma density ramp plays an important role to make self-focusing stronger which leads to enhance the second harmonic generation in plasma.

High-order harmonic generation in plasmas from nanoparticle and mixed metal targets at 1-kHz repetition rate

High-order harmonic generation in laser-produced plasmas from nanoparticle and mixed metal targets is studied using a femtosecond Ti:sapphire laser operating at 1-kHz repetition rate. Mixed plasmas from brass and plasmas from nanoparticles (Al, carbon) are investigated and compared to their monatomic counterparts of Zn, Cu, and Al. The dependence on the delay between the heating ablation pulse and the driving converting pulse is studied for a light (carbon) and a heavy atom (silver) target. Further, we report on a comparative measurement of the efficiencies and the photon flux from argon gas harmonics and carbon plasma harmonics. For our conditions, the 13th harmonic is generated in a carbon plasma with an efficiency of η = 5.3 × 10−7 and yields a flux of about 9.8 × 1010 photons s−1, about 40 % higher than the corresponding harmonic flux in Ar gas under otherwise identical conditions.

Resonant second harmonic generation in plasma by self-focused twisted beam

The resonant second harmonic generation in the presence of a wiggler magnetic field by twisted laser plasma interaction is surveyed. The wiggler magnetic field provides additional momentum required for the phase matching. The Laguerre–Gaussian modes can be used to control the self-focusing and improve the second harmonic generation in laser plasma interaction. The wave equations for the fundamental and the second harmonic fields have been solved in the paraxial approximation. The generation of the second harmonic considering self-focusing is investigated. Also, the dependence of the second harmonic power on the propagation distance for different values of initial fundamental beam intensity, vortex charge number of the doughnut main beam and plasma density has been obtained.

Advantages of plasma harmonic generation using high pulse repetition rate lasers: Review of recent studies

The studies of coherence properties of the harmonics generating in laser-produced plasmas, the analysis of the optical nonlinearities of deoxyribonucleic acid components, the resonance enhancement of harmonic in the cases of excitation of indium plasma by multi- and few-cycle pulses, and the application of nanoparticle-based emitters of harmonics using high-pulse repetition rate lasers are reviewed. The analysis of various aspects of plasma harmonic generation at the conditions of optimal excitation of the ablated targets irradiating by 1 kHz lasers is presented. The growth of plasma harmonic conversion efficiency, single harmonic emission, nonlinear spectroscopy of complex organic components, as well as high coherency of harmonic radiation show the advantages of using plasma harmonic technique for optimization of the sources of coherent extreme ultraviolet radiation and for the material science studies. These studies allowed a significant growth of the average power of harmonics compared with the case of 10 Hz lasers.

Application of double femtosecond pulses for plasma harmonic generation

We demonstrate the harmonic generation of the femtosecond pulses propagated in the vicinity of solid targets. The harmonics were observed in the case of double-pulse scheme while using different solids (metals, nanoparticle, and microparticle powders). The efficiency and cut-off of harmonic generation using double-pulse scheme were varied depending on the target and compared with the commonly used method of the laser ablation by the picosecond pulses. The simplicity of this method allows its application in the nonlinear spectroscopy of solids.

New Approaches in Frequency Conversion of Laser Radiation in Plasma Plumes

Recent studies of plasma harmonic generation are reviewed. We show the advances of this technique for generation of coherent ultrashort pulses in the extreme ultraviolet range. Among the achievements highlighted in this review are the comparative experimental and theoretical studies of high-order harmonic generation in silver plasma, isolated subfemtosecond pulse generation in Mn plasma ablation, stable generation of high-order harmonics of femtosecond laser radiation from laser produced plasma plumes at 1 kHz pulse repetition rate, and high-order harmonic generation in fullerenes using few- and multi-cycle pulses of different wavelengths. We show that new developments of plasma harmonic studies can lead to the creation of an attractive field of laser ablation induced high-order harmonic generation spectroscopy.