Showing papers on "High harmonic generation published in 1972"

Ultrasonic Harmonic Generation in Piezoelectric Semiconductors

Abstract: Second‐harmonic generation of ultrasound in piezoelectric semiconductors is investigated using a quantum treatment which is valid at high frequencies and in strong magnetic fields. The effects of collisions are neglected so that our treatment is valid only for ql≫1. It is shown that the amplitude of the second harmonic can be expressed in terms of the fundamental using the linear and nonlinear conductivity tensors. The latter quantities are related to the current densities which are linear and nonlinear in the piezoelectric fields generated by the ultrasound. The linear and nonlinear conductivities are calculated using the parabolic and nonparabolic models for the energy bands of a semiconductor. It is found that only those sound waves which induce longitudinal electric fields will contribute appreciably to second‐harmonic generation. For waves propagating parallel to a magnetic field, we find that the amplitude of the second harmonic is independent of the magnetic field for the parabolic model. It is also found that the acoustic flux in the second harmonic will peak at sound wave vectors of the order of the Debye wave vector. In contrast, for the nonparabolic model it is found that the amplitude of the second harmonic depends upon magnetic field. The results of the calculation are applied to n‐type InSb, and the magnitude of the second‐harmonic generation is estimated for ultrasonic frequencies in the microwave region. It is found that the magnitude of the second harmonic is considerably enhanced using the nonparabolic model over what would be predicted using the parabolic model.

Harmonic Generation of Shallow Water Waves Over Topography

Abstract: We investigate the reflection and nonlinear interaction between the first and second harmonics of a two-dimensional Boussinesq wavetrain. Effects of topography are included, the depth departing from a constant in a finite region. It is found that topography can speed up or retard energy transfer between first and second harmonics. The reflection coefficient in the present context is significantly different from the one obtained by using linear theory. This is partly due to partitioning of energy between harmonics.

Absolute measurement of submillimetre and far infra-red laser frequencies

Abstract: The frequencies of the hydrogen cyanide and water vapour laser emissions have been measured directly against a fundamental frequency standard by harmonic generation and mixing and beat frequency detection in point contact diodes. The value obtained for the HCN laser (337 μm) is 890 760.2 ± 0.2 MHz and for the H2O laser (118 μm) 2 527 952.5 ± 1.5 MHz. In addition some preliminary measurements have been made on the 10.7 THz H2O laser line.

Superlattice harmonic generator & mixer for electromagnetic waves

Abstract: The disclosure relates to a device for generating electromagnetic waves which have wavelengths different from an input wavelength to the device. The device consists of man-made superlattice structure fabricated by epitaxial deposition techniques to which at least one electromagnetic wave is applied. The input wave has an electric field component parallel to the longitudinal axis of the superlattice structure. Because of the special characteristic of the superlattice structure, it is possible to obtain as outputs all the odd harmonics of the input wavelength. By applying an electric field parallel to the longitudinal axis of the superlattice, it is possible to obtain both odd and even harmonics of the input wavelength. By switching the electric field, a gating action is obtained. To select the desired harmonic, appropriate filters are used. Mixing as well as harmonic generation is possible with the arrangements disclosed by applying a plurality of input wavelengths which by multiple photon processes produce outputs having relatively long wavelengths compared to the input wavelength. The mixed outputs in both the presence and absence of an applied electric field are obtainable by filtering. Thus, inputs in the visible range may be mixed to provide outputs in the far infrared region which are not easily obtainable using prior art arrangements.

Subharmonics and jump resonance in a third-order nonlinear system

Abstract: A third-order nonlinear system was simulated on an analog computer and examined for subharmonic frequency generation and jump resonance. The results were compared to existing knowledge of the same phenomena in certain second-order non-linear systems. The results indicate that the systems exhibit comparable subharmonic and jump resonance characteristics.

Alfvén Wave Second‐Harmonic Generation in Bismuth: Kinetic Theory

Abstract: The possible nonlinear mechanisms for harmonic generation in bismuth have been investigated by solving the Boltzmann transfer equation for free carriers. Space diffusion of carriers has been shown to be as important as the interaction of magnetic field of the wave with current density. The results are compared with the experimental results of Bate and Wisseman for damped Alfven wave second‐harmonic generation. Except for the behavior of harmonic power with static magnetic field, a good agreement is found.

Microwave 2nd-harmonic generator of high conversion efficiency using the nonlinearity of negative resistance in n type GaAs

Abstract: Theoretical considerations and experimental studies of a microwave harmonic generator using the nonlinearity of negative resistance in n type GaAs for a small-signal excitation are performed to develop solid-state millimetre-wave devices. Experimental results using a Gunn diode show the very high conversion efficiency and the possibility of millimetre-wave generation.

Harmonic generation by resistive feedback from superconducting point contacts

Abstract: The rf emission from a superconducting point contact driven with a constant current source allows the direct observation of harmonic generation by purely resistive feedback. The amplitudes of the harmonics are shown to be in agreement with the theoretical values determined from a simple model of the junction.

Experiments concerning the nature of trapped-plasma mode harmonic extraction from P + -N-N + avalanche diodes

Abstract: An experimental investigation has clarified the nature of both fundamental and harmonic extraction from p+-n-n+avalanche diodes operated in the trapped-plasma mode. A standard coaxial cavity was found to be suitable for low-order ( n\leq5 ) harmonic generation. Calculations revealed that the circuit behaved as a bandpass filter which allowed power to be extracted at a particular output harmonic while "reactively" terminating the diode at other harmonics. Measurements were made of external current and dV/dt waveforms for illustrative cases of fundamental and low-order harmonic extraction. Integrated dV/dt waveforms exhibited overvoltages which increased with increasing peak displacement currents. In general, the duration of the plasma-removal period of high current increased with increasing overvoltage. Carroll's [16] suggested dichotomy of voltage waveforms into independent reactive and resistive components was found to be appropriate for optimum first and second harmonic extraction. For third, fourth, and fifth harmonic extraction, however, it was observed that optimum efficiency was associated with significant changes in the physical states of the diode. Fourier analysis of the integrated dV/dt waveforms for low-order harmonic extraction revealed that maximum voltage amplitudes occurred at the harmonic being extracted. Combination ridge waveguide coaxial cavities were used for high-order harmonic extraction in X and K band. A far-infrared interferometer detected components in the power spectrum from the K -band cavity at frequencies up to 40 GHz. It was found empirically that, to first order, the optimum observed extraction efficiency was equal to 50 percent/ (harmonic number).

Pulsed laser arrangement

Abstract: A pulsed second harmonic output is obtained from a continuously pumped laser at repetition rates in the 1-10 MHz range. This is accomplished by electrically pulsing an intracavity nonlinear element to establish momentarily the phase-matched condition required for second harmonic generation. The generated harmonic is a high-amplitude optical pulse which is coupled out of the cavity via a harmonic-transparent mirror.

Theory of Parametric Instabilities and Harmonic Generation in Tonks-Dattner Resonances

Abstract: Onedimensional fluid theory of Tonks-Dattner resonances in inhomogeneous, bounded plasmas is extended to stronger exciting electric fields. The relation of parametric instabilities and harmonic generation with Tonks-Dattner resonances will be worked out in a more direct way than in previous work. Electric field thresholds and growth rates for parametric instabilities will be obtained from theory of homogeneous Mathieu equation. Stationary excitation at the driving frequency and its harmonics follows from a particular solution of an inhomogeneous Mathieu equation.

Generation of higher electron cyclotron frequency harmonics in plasma with a beam

Abstract: We examine nonlinear excitation of the higher electron-cyclotron frequency harmonics for waves propagating perpendicular to an external uniform magnetic field in a Maxwell plasma for the case of low-density electron beam passage through the plasma. It is shown that the nonlinear excitation mechanism leads to the possibility of generating cyclotron harmonics for plasma parameters for which generation does not occur from the linear theory viewpoint. The nonlinear cyclotron harmonic generation increments are calculated for nonlinear scattering by the beam and plasma electrons of the high frequency longitudinal waves excited in the plasma by the beam.

Large signal analysis of frequency multiplication using non-linear capacitance†

Abstract: A large signal analysis of frequency multiplication using non-linear capacitance has been made. No restriction on the non-linearity of the dynamic capacitance has been imposed. The amplitude of the nth harmonic voltage has been taken into consideration. Hence a general large signal formula for the optimized efficiency has been derived. The only restriction imposed is the requirement of ideal filters at the input and output establishing the existence of only the fundamental and the required harmonic voltage across the non-linear capacitance. To relate to practical cases of varactor diodes, computation of Fourier generator component of charge coefficients of abrupt and graded junction varactor diodes has been made. Since only the non-linear capacitance mode of harmonic generation is postulated, for numerical calculation the total composite a.c. voltage consisting of the fundamental and the nth harmonic voltage has been assumed to be 90% of the total d.c. voltage inclusive of the applied bias and th...