Showing papers on "Parametric oscillator published in 1993"

Traveling-wave parametric generation of widely tunable, highly coherent femtosecond light pulses

Abstract: We report on the generation of ultrashort tunable pulses with a cavityless traveling-wave scheme consisting of a parametric superfluorescence seed source and a parametric amplifier. We show that the traveling-wave approach, with its advantages of simplicity and direct generation of tunable energetic single pulses, can be used in the femtosecond regime, and to this end we discuss the performances that were obtained with pump pulses of ≈1-ps and 200-fs duration at wavelengths of 0.53 and 0.6 μm, respectively. Of particular interest is the β-barium borate-based traveling-wave parametric generator (type-II phase matching), since it offers the possibility of generating nearly transform-limited pulses that are continuously tunable within a wide spectral range to as high as 3 μm in the IR. With a diffraction-limited pump at 0.53 μm. we obtained tunable pulses in a 1.2× diffraction-limited beam, which could be focused, with an f/20 optics lens, to an intensity of 1013 GW/cm2. A temperature-tuned lithium triborate-based femtosecond parametric generator, with its smaller group-velocity dispersion and absence of walk-off, can operate at a pump energy of as low as 30 μJ in a 200-fs pulse.

Quantum phenomena in nonstationary media

Abstract: The problem of electromagnetic-field quantization in time-dependent nonuniform linear nondispersive media is investigated. The explicit formulas for the number of photons generated from the initial vacuum state due to the change in time of dielectric permeability of the medium are obtained in the case when the spatial and temporal dependences are factorized. The concrete time dependences include adiabatic and sudden changes of permeability, the parametric resonance at twice the eigenfrequency of the mode, Epstein's symmetric and transition profiles, «temporal Fabry-Perot resonator,» and some others

Simulton solutions for the parametric amplifier

Abstract: We introduce new simultaneous, multiple-frequency, solitary-wave solutions to the traveling-wave parametric amplifier. Both degenerate and nondegenerate systems are treated including dispersion. These parametric amplifier simultons are shown to exhibit phase-dependent collisions. Spatial solitary waves are also found in the case of cw fields parametrically coupled in a planar waveguide.

Nonlinear response of a parametrically excited buckled beam

Abstract: A nonlinear analysis of the response of a simply-supported buckled beam to a harmonic axial load is presented. The method of multiple scales is used to determine to second order the amplitude- and phase-modulation equations. Floquet theory is used to analyze the stability of periodic responses. The perturbation results are verified by integrating the governing equation using both digital and analog computers. For small excitation amplitudes, the analytical results are in good agreement with the numerical solutions. The large-amplitude responses are investigated by using a digital computer and are compared with those obtained via an analog-computer simulation. The complicated dynamic behaviors that were found include period-multiplying and period-demultiplying bifurcations, period-three and period-six motions, jump phenomena, and chaos. In some cases, multiple periodic attractors coexist, and a chaotic attractor coexists with a periodic attractor. Phase portraits, spectra of the responses, and a bifurcation set of the many solutions are presented.

Continuous-wave singly resonant optical parametric oscillator pumped by a single-frequency resonantly doubled Nd:YAG laser

Abstract: We report what is to our knowledge the first demonstration of a continuous-wave singly resonant optical parametric oscillator based on potassium titanyl phosphate. The pump source used is a single-frequency resonantly doubled Nd:YAG laser. By double passing the pump through the crystal, we achieved a minimum oscillation threshold of 1.4 W. With 3.2 W of incident pump power, a maximum 1.07 W of nonresonant idler power was generated. Spectral measurement reveals that the singly resonant optical parametric oscillator operates consistently in a single axial mode with much relaxed axial mode hop tolerance to cavity length and pump-frequency fluctuations compared with doubly resonant optical parametric oscillators previously demonstrated.

Quadruply resonant optical parametric oscillation in a monolithic total-internal-reflection resonator

Abstract: Monolithic total-internal-reflection resonators are low-loss broadband devices that permit variable input–output coupling. They are ideally suited as resonators for high-efficiency low-threshold widely tunable continuous-wave optical parametric oscillation. We demonstrate a continuous-wave quadruply resonant MgO:LiNbO3 optical parametric oscillator in which doubly resonant second-harmonic generation and doubly resonant optical parametric oscillation occur simultaneously. The threshold subharmonic power at 1.06 μm for oscillation near 1.06 μm is 0.4 mW. Stable single-frequency operation is achieved, and the tuning curve is measured.

Noncritically phase-matched continuous-wave mode-locked singly resonant optical parametric oscillator synchronously pumped by a Ti:sapphire laser

Abstract: Efficient operation of a cw mode-locked singly resonant optical parametric oscillator of noncritically phase-matched KTiOPO4 is demonstrated. The optical parametric oscillator is synchronously pumped by an 82-MHz-repetition-rate mode-locked Ti:sapphire laser with pump-pulse lengths of 1.4 ps. We accomplished tuning of the optical parametric oscillator by tuning the wavelength of the pump laser. A variation of the Ti:sapphire laser wavelength in the range 720 nm < λp < 853 nm tunes the signal wave from 1.052 μm < λ < 1.214 μm and the idler wave from 2.286 < λi < 2.871 μm. We achieved stable operation with transform-limited pulses of 1.2-ps length over the entire tuning range. We obtained 700 mW of maximum average output power at the maximum of the tuning curve for the idler and signal waves, corresponding to an efficiency of 42%.

All-solid-state synchronously pumped optical parametric oscillator

Abstract: The design and performance of a continuously operated singly resonant synchronously pumped potassium titanyl phosphate optical parametric oscillator is described. With an all-solid-state pump source providing 2-ps pulses at 523 nm, we found that the oscillation threshold pump intensity was ~60 MW cm−2, in good agreement with design calculations. The output of the optical parametric oscillator provided transform-limited pulses of 1–2-ps duration at a 125-MHz repetition rate, continuously tunable over the range of 938–1184 nm, with tens of milliwatts of average power.

Study of the parametric oscillator driven by narrow‐band noise to model the response of a fluid surface to time‐dependent accelerations

Abstract: A stochastic formulation is introduced to study the large amplitude and high‐frequency components of residual accelerations found in a typical microgravity environment (or g‐jitter). The linear response of a fluid surface to such residual accelerations is discussed in detail. The analysis of the stability of a free fluid surface can be reduced in the underdamped limit to studying the equation of the parametric harmonic oscillator for each of the Fourier components of the surface displacement. A narrow‐band noise is introduced to describe a realistic spectrum of accelerations, that interpolates between white noise and monochromatic noise. Analytic results for the stability of the second moments of the stochastic parametric oscillator are presented in the limits of low‐frequency oscillations, and near the region of subharmonic parametric resonance. Based upon simple physical considerations, an explicit form of the stability boundary valid for arbitrary frequencies is proposed, which interpolates smoothly between the low frequency and the near resonance limits with no adjustable parameter, and extrapolates to higher frequencies. A second‐order numerical algorithm has also been implemented to simulate the parametric stochastic oscillator driven with narrow‐band noise. The simulations are in excellent agreement with our theoretical predictions for a very wide range of noise parameters. The validity of previous approximate theories for the particular case of Ornstein–Uhlenbeck noise is also checked numerically. Finally, the results obtained are applied to typical microgravity conditions to determine the characteristic wavelength for instability of a fluid surface as a function of the intensity of residual acceleration and its spectral width.

Stabilization and tuning of a doubly resonant optical parametric oscillator

Abstract: We present experimental results of frequency tuning and stabilization of a type-II phase-matched potassium titanyl phosphate (KTP) doubly resonant optical parametric oscillator. Four tuning elements were employed to control the stability and tuning of the parametric oscillator. Discrete frequency tuning of a nearly degenerate optical parametric oscillator over a range of ~3 THz was obtained by crystal angle tuning and cavity-length scanning. We achieved continuous frequency tuning over a 0.5-GHz range through the use of temperature and electro-optic tuning of the KTP crystal. Using these frequency-control techniques, we phase locked the signal–idler beat frequency to an external microwave frequency source, thus demonstrating tunable optical frequency division. The power spectral density of the residual phase noise of the phase-locked signal–idler beat note was measured to be 0.3mrad/Hz. Characteristics of two different cavity designs, their operations, tuning behavior, and stability issues are examined.

Spatial structure of a squeezed vacuum.

Abstract: We analyze the quantum properties of the signal near field emitted by a degenerate parametric oscillator below threshold, including diffraction and its effects on the threshold for signal generation. The field is probed by a local oscillator field of arbitrary spatial configuration. The results are expressed in terms of an appropriate spectrum which describes how the level of squeezing varies with the angle from the direction of propagation. The results hold for cavities both with plane and with spherical mirrors.

Limits to squeezing and phase information in the parametric amplifier.

Abstract: We investigate the time evolution of squeezing in the signal mode of the undamped parametric amplifier. Both the degenerate and nondegenerate cases are considered. These are the simplest models that give limits to squeezing caused by both the intrinsic pump noise and pump depletion. Conflicting analytic expressions have been reported. We resolve this by the use of exact numerical methods, employing both number state and stochastic techniques. Our central result is that in both cases we find that the minimum in the squeezed quadrature variance scales as N-1/2, where N is the initial coherent pump photon number. This bound on the amount of squeezing obtainable, coupled with the loss in energy due to the conversion efficiency, serves to limit the phase information in the squeezed channel to no more than that of the coherent pump. We believe this to be a fundamental limit for using the squeezed radiation generated in coherently driven parametric amplifiers.

Coherent-state propagator of the generalized time-dependent parametric oscillator

Abstract: In this paper we derive the coherent-state propagator of a generalized time-dependent parametric oscillator using the Lie algebraic approach. The method is simple and gives the same results as those obtained by the path integral approach. Furthermore, this Lie algebraic approach can be easily generalized to a time-dependent many-body system once the algebraic structure of its Hamiltonian is identified.

Continuous-wave parametric oscillation in lithium triborate.

Abstract: We demonstrate a continuous-wave optical parametric oscillator that uses lithium triborate as the nonlinear material in a temperature-tuned noncritical phase-matched type I geometry. Pumped at 514.5 nm, the triply resonant oscillator has a threshold of 50 mW. We obtain peak output powers of 90 mW corresponding to a 10% external conversion efficiency and measure a tuning range of 0.966 to 1.105 μm, limited by the bandwidth of the mirrors. Operating the optical parametric oscillator both at and away from degeneracy, we observe rapid changes in output power as a function of cavity length owing to competition between signal and idler mode pairs.

Effect of plasma on efficiency enhancement in a high power relativistic backward wave oscillator

Abstract: A linear theory of the excitation of electromagnetic waves in a plasma-filled backward-wave oscillator driven by an intense relativistic electron beam is presented. It is found that the spatial growth rate of backward-wave instability exhibits a resonant increase for a particular value of fill-plasma density. Results are compared to the results of an experiment by K. Minami et al. (1988) on a high-power backward-wave oscillator. >

On critical-layer and diffusion-layer nonlinearity in the three-dimensional stage of boundary-layer transition

Abstract: This paper considers nonlinear interactions in the three-dimensional stage of transition to turbulence, taking an accelerating boundary layer as a prototype flow. Attention is focused on transition via subharmonic resonance in the upper-branch scaling regime. It is shown that the (weakly) nonlinear instability of the flow is described by a seven-zoned structure, cf. the five-zoned structure for the linear problem. The dominant nonlinear interactions take place both in a critical layer and in ‘diffusion layers’. The nonlinearly generated mean flow in turn interacts with the wall to attain a maximum magnitude near the wall. It is emphasized that both the nonlinear mechanism and the flow structure are generic for three-dimensional disturbances. And there is some similarity with the work in the context of wave/vortex interaction. Numerical solutions of the amplitude equations indicate that if the oblique modes initially have a small amplitude, they first experience a rapid growth caused by parametric resonance. Following this the cubic interactions of the oblique modes inhibit the growth and lead to a wavelength shortening. However, if the initial amplitudes of the oblique modes are sufficiently large, the parametric resonance can be completely bypassed. Numerical solutions also suggest that oblique modes with unequal initial amplitudes evolve to an equal-amplitude state.

On the linear theory of the elastic pendulum

Abstract: A harmonic oscillator in a gravitational field, such as a weight on a spring, sometimes exhibits loss of lateral stability due to parametric resonance. The resulting horizontal, or pendulum oscillation is analysed by means of a locus line drawn in the Ince-Strutt stability chart of the respective Mathieu equation, to determine graphically the range of mass leading to instability for a particular amplitude of the initially vertical oscillation and the corresponding growth coefficient.

Nonlinear wave coupling and subharmonic resonance in planar jet shear layer transition

Abstract: An experimental investigation of the nonlinear spectral development associated with the transition of an initially laminar planar jet shear layer is presented. The local shear layer spectral dynamics are modeled as a nonlinear system containing both linear and quadratically nonlinear system elements. A novel digital signal processing technique is applied which allows the linear and quadratically nonlinear wave coupling coefficients that characterize the local spectral dynamics to be estimated directly from time‐series velocity fluctuation data. The method utilized is noniterative and explicitly includes fourth‐order spectral moments. From the linear coupling coefficient, the local spatial growth rate and dispersion relation may be obtained. Of particular interest in the work reported is the associated nonlinear wave coupling coefficient which provides a measure of the efficiency of local nonlinear three‐wave coupling. These show that the jet shear layer exhibits a strong preference for difference mode interactions. With the estimation of the related nonlinear power transfer function, the total, linear, and quadratic nonlinear spectral energy transfer may be locally estimated. When these measures are used in conjunction with the local quadratic bicoherency and local linear–quadratic coupling bicoherency, the local nonlinear spectral dynamics of the flow may be completely and unambiguously quantified. Particular emphasis is placed upon discerning the mechanism which gives rise to subharmonic resonance with the fundamental. Results show that the amplification of the subharmonic occurs via a parametric resonance with the fundamental rather than by direct quadratic difference interaction. That is, the subharmonic is boosted by a weakly nonlinear mechanism involving a linear growth rate modification due to a resonant phase lock with the fundamental instability.

Theoretical and experimental study of the nonlinearity coupled heave, pitch, and roll motions of a ship in longitudinal waves

Abstract: The loss of dynamic stability and the resulting large-amplitude roll of a vessel in a head or following sea were studied theoretically and experimentally. A ship with three degrees of freedom (roll, pitch, heave) was considered. The governing equations for the heave and pitch modes were linearized and their harmonic solutions were coupled with the roll mode. The resulting equation, which has time varying coefficients, was used to predict resonance in roll. The principal parametric resonance was considered in which the excitation frequency is twice the natural frequency in roll. Force- response phenomena and multiple stable solutions for the case of subcritical instability was observed in the experiments and found to be in good qualitative agreement with the results predicted by the theory. The experiments also revealed that the large-amplitude roll is dependent on the location of the model in the standing waves.

Continuous-wave parametric oscillator pumped in the ultraviolet.

Abstract: We demonstrate what is to our knowledge the first continuous-wave optical parametric oscillator pumped by an ultraviolet source. An argon-ion laser operating at 364 nm is used to pump the nonlinear material lithium triborate, which generates tunable radiation in the blue-green and near-infrared spectral regions. With the cavity stabilized to stay on a single-frequency mode pair, we measure a threshold of 115 mW and a maximum output power of 103 mW. By use of a noncritical phase-matched, type II geometry, tuning ranges from 502 to 494 nm (signal) and 1.32 to 1.38 μm (idler) are observed.

Combating dispersion with parametric amplifiers

Abstract: A novel approach to combating the pulse broadening effect of group-velocity dispersion in a fiber-optic communication link is presented. In the scheme linear loss in the fiber is balanced by a chain of periodically spaced, phase-sensitive, degenerate optical parametric amplifiers. Analysis of pulse propagation in such a fiber line shows that, due to attenuation in the quadrature orthogonal to the amplified quadrature, it is possible for a pulse to propagate without significant broadening over lengths much longer than the usual dispersion length of the fiber. >

Widely tunable synchronously pumped optical parametric oscillator.

Abstract: We describe a continuous-wave synchronously pumped singly resonant lithium triborate optical parametric oscillator that is tuned over the range 0.8–1.5 μm. At four times threshold, the pump depletion is 75%, and the oscillator converts 27% of the pump radiation into tunable output in picosecond pulses with 78-mW average power.

Temperature compensated oscillator circuit

Abstract: Dual mode oscillator (9), e.g. to be used in a temperature compensated circuit in which during operation at least a first oscillation having a fundamental frequency and a second oscillation having a second frequency occurs, which second oscillation is substantially equal to a, preferably the third, harmonic of the first frequency, both said oscillations generating a first and a second oscillation signal, respectively, that may be combined to generate a signal having a substantially linear temperature dependency, the oscillator (9) comprising an electronic controllable switch (S1) connected in such a way that in a first state the oscillator (9) oscillates in the first oscillation and in its other state the oscillator (9) oscillates in the second oscillation, the oscillator (9) having at least one output supplying alternately said first (f1) and said second oscillation signal (f3).

Homodyne photon statistics of the subthreshold degenerate parametric oscillator

Abstract: Homodyne statistics when the light from a degenerate parametric oscillator (DPO) is mixed with coherent light from a local oscillator are discussed. By using dynamical models of these beams we discuss the photon sequences underlying the superposed beam in terms of photoelectric pulse sequences recorded by a detector. The field produced by the parametric oscillator is expressed in terms of two independent real Gaussian random variables. Using this property of the field variables, we derive the generating function for the photoelectron statistics analytically. From this generating function, expressions for the photoelectron-counting distribution, factorial moments, and the waiting-time distribution are derived. These quantities are directly measurable in photon-counting experiments. The results reported here are applicable to arbitrary strengths of the signal and the local-oscillator fields. We also show that, depending on the relative strength and relative phase between coherent light from the local oscillator and squeezed light from the DPO, the superposed light beam may exhibit many interesting nonclassical features. These and other effects are described and curves are presented to illustrate the behavior.

A quasioptical resonant-tunneling-diode oscillator operating above 200 GHz

Abstract: A quasioptical resonant-tunneling-diode (RTD) oscillator is demonstrated at frequencies above 200 GHz. The oscillator is stabilized by a semiconfocal open cavity. The maximum output power and the linewidth are approximately 50 mu W and 20 kHz, respectively, at a fundamental frequency of 210 GHz. By varying the cavity length, the oscillator frequency can be adjusted over a 0.4-GHz range in a repetitive manner. This behavior is explained by analogy with laser oscillators. The quasioptical RTD oscillator is well suited as a local oscillator for low-power radiometric mixers. >

β-Barium borate and lithium triborate picosecond parametric oscillators pumped by a frequency-tripled passive negative-feedback mode-locked Nd:YAG laser

Abstract: We report on an investigation of a singly resonant picosecond optical parametric oscillator in a noncollinear configuration for which we alternatively used β-barium borate and lithium triborate in a type-I phase-matching configuration tunable from 407 to 2780 nm and from 452 and 1650 nm, respectively. The parametric oscillator was synchronously pumped by the third harmonic of a passive negative-feedback actively–passively mode-locked Nd:YAG laser–amplifier system, and long and flat trains of short bandwidth-limited 9-ps pulses were produced. We obtained conversion efficiency into the idler wave (at 900 nm) of as high as 10% and overall efficiency as high as 26%. We present a numerical model of the operation that agrees very well with the experimental results. The simplicity and ruggedness are the main strengths of this source when high-power conversion capability and wide tunability are the main requirements.