Proper Phase Matching Research Articles

Numerical Investigation of the Temporal Contrast in ps-OPCPA with Compact Double BBO Arrangement

The picosecond optical parametric chirped pulse amplifier (ps-OPCPA) with double BBO arrangement can support the ultrabroad spectrum even under a relatively long pump pulse duration (∼100 ps). In this work, five-wave-coupled equations taking into consideration different phase matching conditions between the parametric superfluorescence (PSF) and the signal are proposed to investigate the temporal contrast in ps-OPCPA schemes. Both the temporal contrast and the amplified spectrum are numerically analyzed in double BBO arrangements with four phase matching conditions. Numerical results show that the high temporal contrast and ultrabroad spectrum can be simultaneously realized by choosing the proper phase matching geometry in a double BBO arrangement. The numerical investigation here relaxes the requirement of very short pump pulses in ps-OPCPA, which can provide beneficial guidance for the design and construction of ps-OPCPA.

Design and development of 42GHz transmission line for ECRH application

This work represents the design and development of overmoded circular waveguide- based mode converters. It transforms unpolarized mode into linearly polarized mode used in plasma applications. This transmission line system (TLS) consists of TE03 to HE11 mode converters, corrugated waveguides, and other components. These are used to carry 200 kW power generated from gyrotron at a frequency of 42±0.2 GHz to the applicator or dummy load (in offload condition).A conservative design goal of insertion loss (1.5 dB) for the TLS is used as a design driver. It consists of different overmoded circular waveguide mode converters, miter bends (MBs), and corrugated waveguide. For efficient transmission of power between components, proper phase matching and accurate calculations of geometrical dimensions (perturbation amplitude, bending angle, and many more) are prerequisites. Analytical study, design technique, manufacturing process and simulation studies of TLS are discussed and summarized. After carrying out simulation studies of the various TLS components, the estimated insertion loss of the TLS is approximately 1.3 dB.The TLS along with seals is compatible to high vacuum (10−6 torr) and pressurization of 1 bar absolute pressure. Similar joints have been used at the joints of the various components in the TLS. The worst case leak rate of any of the TLS joint seal is 10−6 mbar liter per second.

Transverse phase matching of high-order harmonic generation in single-layer graphene.

The efficiency of high-harmonic generation (HHG) from a macroscopic sample is strongly linked to the proper phase matching of the contributions from the microscopic emitters. We develop a combined micro+macroscopic theoretical model that allows us to distinguish the relevance of high-order harmonic phase matching in single-layer graphene. For a Gaussian driving beam, our simulations show that the relevant HHG emission is spatially constrained to a phase-matched ring around the beam axis. This remarkable finding is a direct consequence of the non-perturbative behavior of HHG in graphene-whose harmonic efficiency scaling is similar to that already observed in gases- and bridges the gap between the microscopic and macroscopic HHG in single-layer graphene.

Terahertz radiation generation by pulse slippage of Cosh-Gaussian lasers in a corrugated magnetized plasma

The combined effects of pulse slippage and the transverse magnetic field are studied on terahertz radiation excitation by nonlinear beating of two cosh-Gaussian (ChG) laser pulses propagating in a corrugated plasma. The beating lasers exert nonlinear ponderomotive force on plasma electrons. The oscillating electrons couple with corrugations present in the plasma and resonantly excite a nonlinear current (at different frequencies) which drive the terahertz wave at proper phase matching conditions. As the group velocity of THz radiation is higher than the group velocity of beating lasers, the THz pulse slips forward the pump lasers, and its saturation takes place. The effects of THz wave frequency, the decentred parameter (of beating lasers), the periodicity of the density structure, and the applied dc magnetic field are studied on THz emission. An efficiency of ∼10−4 is achieved for a laser intensity of ∼2×1015 W/cm2 (at a laser wavelength of ∼10.6 μm for the CO2 laser).

Generation of terahertz radiation by intense hollow Gaussian laser beam in magnetised plasma under relativistic-ponderomotive regime

This paper explores the self-focusing of hollow Gaussian laser beam (HGLB) in collisionless magnetized plasma and its effect on the generation of THz radiation in the presence of relativistic-ponderomotive nonlinearity. The relativistic change of electron mass and electron density perturbation due to the ponderomotive force leads to self-focusing of the laser beam in plasma. Nonlinear coupling between the intense HGLB and electron plasma wave leads to generation of THz radiation in plasma. Resonant excitation of THz radiation at different frequencies of laser and electron plasma wave satisfies proper phase matching conditions. Appropriate expressions for the beam width parameter of the laser beam and the electric vector of the THz wave have been evaluated under the paraxial-ray and Wentzel-Kramers Brillouin approximations. It is found that the yield of THz amplitude depends on the focusing behaviour of laser beam, magnetic field, and background electron density. Numerical simulations have been carried out to investigate the effect of laser and plasma parameters on self-focusing of the laser beam and further its effect on the efficiency of the generated THz radiation.

Second harmonic generation by self-focusing of intense hollow Gaussian laser beam in collisionless plasma

The effect of self focused hollow Gaussian laser beam (HGLB) (carrying null intensity in center) on the excitation of electron plasma wave (EPW) and second harmonic generation (SHG) has been investigated in collisionless plasma, where relativistic-ponderomotive and only relativistic nonlinearities are operative. The relativistic change of electron mass and the modification of the background electron density due to ponderomotive nonlinearity lead to self-focusing of HGLB in plasma. Paraxial ray theory has been used to derive coupled equations for the self focusing of HGLB in plasma, generation of EPW, and second harmonic. These coupled equations are solved analytically and numerically to study the laser intensity in the plasma, electric field associated with the excited EPW, and the power of SHG. Second harmonic emission is generated due to nonlinear coupling between incident HGLB and EPW satisfying the proper phase matching conditions. The results show that the effect of including the ponderomotive nonlinearity is significant on the generation of EPW and second harmonic. The electric field associated with EPW and the power of SHG are found to be highly sensitive to the order of the hollow Gaussian beam.

Strong terahertz field generation by relativistic self-focusing of hollow Gaussian laser beam in magnetoplasma

AbstractThe present paper proposes a model for the generation of Terahertz (THz) radiation by self-focused hollow Gaussian beam (HGB) in collisionless magnetized rippled density plasma. At high intensities, the change in the electron mass occurs due to relativistic effect, introducing a nonlinearity in the plasma leading to the self-focusing of the HGB. The nonlinear interaction of this highly intense self-focused HGB with the electron plasma wave in the rippled density plasma, satisfying proper phase matching conditions, results in the resonant excitation of THz radiations at the beat frequency. We have studied the dependence of generated THz radiations on the order of the HGB as well as on the static background magnetic field. The results show that the intensity of the generated radiations is highly sensitive to both of these parameters. For the current scheme the power of the generated THz waves comes out to be of the order of Gigawatts.

THz generation by self-focusing of hollow Gaussian laser beam in magnetised plasma

A scheme of terahertz (THz) generation is proposed by the self-focusing of a high-power laser beam having hollow Gaussian intensity profile in a collissionless magnetized plasma, where ponderomotive nonlinearity is operative. THz waves are resonantly excited at the difference frequency of laser and electron plasma wave (EPW) satisfying the proper phase matching conditions. In this paper first we have investigated the filamentation of the circularly polarized hollow Gaussian beam (HGB) propagating parallel to the direction of a static background magnetic field within the paraxial approximation, subsequently this filamented HG laser beam interplay with the electron plasma wave to generate a nonlinear current in the transverse direction, thereby producing THz radiations. The intensity of the emitted radiations are found to be highly sensitive to the order of the HGB. For the current scheme the power level of THz wave comes out to be gigawatts.

Communication: atomic force detection of single-molecule nonlinear optical vibrational spectroscopy.

Atomic Force Microscopy (AFM) allows for a highly sensitive detection of spectroscopic signals. This has been first demonstrated for NMR of a single molecule and recently extended to stimulated Raman in the optical regime. We theoretically investigate the use of optical forces to detect time and frequency domain nonlinear optical signals. We show that, with proper phase matching, the AFM-detected signals closely resemble coherent heterodyne-detected signals. Applications are made to AFM-detected and heterodyne-detected vibrational resonances in Coherent Anti-Stokes Raman Spectroscopy (χ((3))) and sum or difference frequency generation (χ((2))).

Diode-pumped laser and self-frequency-doubling properties of a Nd^3+:Na_3La_9O_3(BO_3)_8 crystal

We report efficient, diode-pumped, self-frequency doubling (SFD) in the newly developed laser crystal Nd3+:Na3La9O3(BO3)8 (Nd:NLBO). More than 730 mW of fundamental output power at 1072 nm was achieved with a slope efficiency of 16.2%. With incident pump power of 8 W, 29 mW of green cw laser emission at 536 nm was observed with proper phase matching. This initial performance and the good optical properties of the crystalline host are encouraging for the development of a high power diode-pumped SFD visible light laser source.

Phase matching for surface plasmon enhanced second harmonic generation in a gold grating slab

Surface plasmon enhanced second harmonic generation in gold grating slabs was investigated. The efficiency is analyzed with respect to the phase matching at the fundamental and the second harmonic frequencies. A classical electromagnetic model was developed under the weak nonlinearity approximation and solved by the finite element method. The measured zeroth order transmitted second harmonic intensity was found to be in quantitative agreement with numerical results. It is shown experimentally and numerically that proper phase matching at both frequencies improves the second harmonic efficiency.

Spatial fingerprint of quantum path interferences in high order harmonic generation

We have spatially and spectrally resolved the high order harmonic emission from an argon gas target. Under proper phase matching conditions we were able to observe for the first time the spatial fine structure originating from the interference of the two shortest quantum paths in the harmonic beam. The structure can be explained by the intensity-dependent harmonic phase of the contributions from the two paths. The spatially and spectrally resolved measurements are consistent with previous spatially integrated results. Our measurement method represents a new tool to clearly distinguish between different interference effects and to potentially observe higher order trajectories in the future with improved detection sensitivity. Here, we demonstrate additional experimental evidence that the observed interference pattern is only due to quantum-path interferences and cannot be explained by a phase modulation effect. Our experimental results are fully supported by simulations using the strong field approximation and including propagation.

Analysis of active control of metal transfer in modified pulsed GMAW

In the active control of metal transfer of modified pulsed current gas metal arc welding (GMAW) through proper phase matching of the detaching electromagnetic force and the downward momentum of the droplets, one drop detachment per pulse (ODDPP) mode can be achieved reliably at a pulse current lower than the critical transition value. An analytical model is developed to analyse the droplet oscillation and detachment process and the effect of pulse parameters on the dynamic behaviour of metal transfer in active control of metal transfer of modified pulsed current GMAW. The model lays the foundation of optimum selection of welding process parameters in achieving the metal transfer mode of ODDPP in the active control of metal transfer during modified pulsed GMAW.

On the phase matching conditions in applications of one-dimensional photonic band gap structures for nonlinear frequency conversion

Band edge effects such as increased density of modes, large field enhancement, and low group velocity will provide highly efficient parametric interaction if the proper phase matching conditions are established in one-dimensional photonic band gap (PBG) structures. The analysis of the dispersion properties of one-dimensional PBG structure allows us to define the suitable phase matching conditions for parametric interaction when quadratic nonlinear materials constitute the layered geometry.

Dispersive properties of one-dimensional photonic band gap structures for second harmonic generation

We analyse the dispersive properties of one-dimensional photonic band gap structures, and discuss applications to phase matching conditions in the case of second harmonic generation. Band edge effects such as increased density of modes, large field enhancement, and low group velocity induce highly efficient parametric amplification, provided the proper phase matching conditions can be established. Direct integration of Maxwell's equations in the time domain confirms these conclusions, and shows that parametric amplification in one-dimensional photonic band gap structures provide much larger conversion efficiencies compared with ordinary quasi-phase-matching devices.

Diode-pumped self-frequency doubling in a Nd3+:YCa4O(BO3)3 laser

We report efficient, diode-pumped, self-frequency doubling (SFD) in the newly developed laser crystal Nd3+:YCa4O(BO3)3. More than 350 mW of fundamental output power at 1060 nm was achieved with a slope efficiency of 51%. With one watt of absorbed pump power, 62 mW of green cw laser emission at 530 nm was observed with proper phase matching. This initial performance, and the good optical properties of the crystalline host, are encouraging for the development of a high power diode-pumped SFD visible light laser source.

Infrared short pulse measurements with tellurium

Measurement of ultra short light pulses as generated by a mode-locked laser system, requires an overall detection bandwidth of more than 3 GHz. For the visible and the NIR, detection systems, capable of handling pulses in the order of several picoseconds, are available. In this regime nonlinear optical methods have proven to be very suitable. Especially in the visible region they have been very successful. The methods are based on either multi photon fluorescence or second harmonic generation. In the IR region the development of this technology is hampered by the lack of suitable nonlinear materials. A promising and relatively inexpensive technique-but not used anywhere-for background free measurements in the IR is based on second harmonic generation in Tellurium, using type II phase matching of noncollinear beams. The geometry at the crystal is schematically shown in Fig. I. A proper matching of the phase conditions is very sensitive with respect to the angle I)~($~ = 7c - 21)) between the two fundamental beams and the exact orientation of the crystal, whose y-axis should coincide with the bisector of the angle between the incoming beams. A careful analysis of the geometry used and some vector calculus yield that for good operation the angle between the two fundamental beams should be within 0.2” from the theoretical value, which is a very stringent condition. However, it is fairly easy to meet these requirements by just rotating the crystal around the z-axis. In this way, a proper tuning of the angle between the fundamental beams and thus a proper phase matching is easily achieved. This is demonstrated in Figs 2 and 3. In these figures, the squares represent experimental data, and the solid curves are the results of computer calculations. From Fig. 2 we see that a misalignment in & of only 0.2” already yields a signal-drop of 80%. The tremendous effect caused by a mismatch of only 1.65“ is easily compensated by rotation of the crystal around the z-axis over an angle y of about 23”, as is demonstrated in Fig. 3. Guided by these results, we constructed an autocorrelator of standard design, using a noncollinear setup. Using this device, we were able to measure pulses emerging from a mode-locked multi-atmosphere CO, laser. We fired the entire pulse train, thus measuring the averaged pulse length, weighted over the intensity of the individual pulses. The measured autocorrelation function

Theory of Stokes and anti-Stokes generation by Raman frequency conversion in the transient limit.

Analytic and numerical solutions are obtained for the equations describing the propagation of several pulses of different frequencies through a Raman medium. The transient case is treated, and the analysis includes Stokes, pump, and anti-Stokes frequency components. The effect of phase mismatch \ensuremath{\Delta}k between these waves is investigated. An analytic solution is found that describes the phenomenon of transient Stokes--anti-Stokes gain suppression in the limit \ensuremath{\Delta}k=0. For nonzero values of \ensuremath{\Delta}k, the behavior of the transient gain coefficient is found to follow a scaling rule that is the analog of a similar result known from the steady-state limit. Calculations are performed to identify conditions that enhance conversion to anti-Stokes radiation. It is found that there is an optimum strength of the Stokes seed, and that proper phase matching of the initial waves is essential.