Showing papers on "High harmonic generation published in 1987"

Self-organized phase-matched harmonic generation in optical fibers.

Abstract: We generated second-harmonic light from a single-mode fiber after a few minutes of seeding with 532-nm harmonic light along with 1.064-μm pump light. This experiment supports a mechanism for photoinducing an alternating second-order nonlinearity in the fiber.

High average power harmonic generation

Abstract: High average power frequency conversion using solid-state nonlinear materials is discussed. Recent laboratory experience and new developments in design concepts show that current technology, a few tens of watts, may be extended by several orders of magnitude. For example, using KD*P, efficient doubling (> 70 percent) of Nd:YAG at average powers approaching 100 KW is possible; for doubling to the blue or UV regions the average power may approach 1 MW. Configurations using segmented apertures permit essentially unlimited scaling of average power. High average power is achieved by configuring the nonlinear material as a set of thin plates with a large ratio of surface area to volume, and cooling the exposed surfaces with a flowing gas. The design and material fabrication of such a harmonic generator is well within current technology.

Local and nonlocal surface nonlinearities for surface optical second-harmonic generation.

Abstract: We investigate the physical origins of the surface nonlinear susceptibility responsible for surface optical second-harmonic generation. Experiments performed on simple covalent systems were designed to distinguish between the nonlocal electric-quadrupole-type nonlinearity induced by field discontinuity and the local intrinsic, electric-dipole-type nonlinearity of a surface or interface. We find that both mechanisms could operate: The latter usually dominates when the surface layer has a strong structural asymmetry with the fundamental or the second-harmonic frequency at resonance with a dipole-allowed transition.

Second-harmonic generation in fibers

Abstract: In this analytical paper, a formalismfor second-harmonic and sum-frequency generation in glass fibers is developed. It considers only the lowest-order nonlinearities in regular, step-index fibers. Plots showing the dependence of index-matching frequencies on the core radius and index difference across the core-cladding interface are given. Estimates are given for the conversion efficiencies due to the nonlinear polarization at the core-cladding interface and the bulk nonlinear polarization proportional to E ∇E, which includes quadrupolar terms. It is concluded that the interface effects would be dominant. Calculations for the longitudinal-electric-field-induced nonlinear polarization proportional to E2 that involve the same mode coupling are also included. The calculated conversion efficiencies are small and cannot explain the recently observed high conversion efficiencies that were obtained under nonindex-matched conditions. A maximum conversion efficiency of around 10−5 is predicted under index-matching conditions.

Generation of blue cw coherent radiation by sum frequency mixing in KTiOPO4

Abstract: The wavelength, angle, and temperature tolerances of a new room‐temperature noncritically phase‐matched frequency mixing process involving type II frequency mixing of 1064 and 809 nm radiation in potassium titanyl phosphate (KTiOPO4) are measured. The angular and temperature bandwidths are found to be unusually wide. Device applications for upconversion of diode pumped neodymium:yttrium aluminum garnet laser sources to the blue spectral region are explored.

Quadrature frequency conversion

Abstract: A technique for frequency conversion of high-power lasers is described which uses two crystals for each conversion step rather than one. The two crystals are oriented so that the waves generated in them are orthogonally polarized. The conversion efficiency of these quadrature arrangements is much less sensitive to laser pulse nonuniformities than that in single-crystal methods. Consequently, very high conversion efficiency is possible for typically nonuniform laser pulses. Realization of the quadrature concept for all types of nonlinear optical processes are described. Data taken on second harmonic generation of Gaussian pulses shows that very high (internal) conversion efficiency is possible ( > 95 percent) over a substantial range of input energy.

Recent Developments In Barium Borate

Abstract: The nonlinear optical properties of β-BaB204 (beta barium borate) are demonstrated in the generation of second through fifth harmonics of 1.06 μm neodymium laser radiation and in optical parametric oscillation pumped by 532-nm radiation. βBaB204 is particularly useful for high average power applications and nonlinear frequency generation in the ultraviolet to wavelengths as short as 200 nm. An internal energy conversion efficiency of 84% for 1064-nm to 532-nm second harmonic generation, and cascaded harmonic conversion to the 213-nm fifth harmonic with 11% overall conversion were obtained. The observed performance agrees well with that predicted by modeling.

Induced spectral broadening about a second harmonic generated by an intense primary ultrashort laser pulse in ZnSe crystals.

Abstract: The induced spectral broadening about a weak non-phase-matched 530-nm second-harmonic pulse is observed by propagating an intense primary 1060-nm picosecond laser pulse through ZnSe crystals. This broadening is attributed to the induced phase modulation of excitation states.

Efficient generation of 200-nm light in β-BaB 2 O 4

Abstract: Efficient generation of 200-nm light is achieved in ..beta..-BaB/sub 2/O/sub 4/ through third harmonic generation of pulsed dye-laser radiation. (AIP)

Optical third-harmonic generation from polydiacetylene thin films deposited by vacuum evaporation

Abstract: Third-harmonic generation measurements have been made on polydiacetylene thin films fabricated by vacuum deposition. The third-order susceptibility was evaluated to be X(3) = 1.4 × 10-11 esu at 1.9 ?m wavelength.

Original technique for third-harmonic-generation measurements in liquids

Abstract: An original technique, with a special design of liquid cell, is proposed for third‐harmonic generation in liquids. The technique is based on a principle of harmonic generation in an infinite medium by focused laser beam applied for liquid cell windows and uses a thin wedge‐shaped liquid compartment. The measurements can be performed in air, and a high precision in cubic susceptibility and refractive index dispersion determination can be obtained. The technique also allows measurements to be made on liquids absorbing at harmonic and fundamental frequencies and in function of external parameters like temperature, pressure, and electric or magnetic fields. Some results for organic solvents are presented and compared with those obtained by other methods.

Physical Processes at High Field Strengths

Abstract: The availability of extraordinarily bright femtosecond ultraviolet sources is rapidly extending the study of atomic responses into an unexplored regime for which the electric field strength is considerably in excess of an atomic unit. As this regime is approached, experiments studying multiple ionization, photoelectron spectra, harmonically produced radiation, and fluorescence all exhibit strong nonlinear coupling. Peak total energy transfer rates on the order of ~ 2 × 10-4 W/atom have been observed at an intensity of ~ 1016 W/cm2, and the removal of an electron from an inner principal quantum shell has been demonstrated in xenon. Measurements of the radiation produced by the high field interaction with the rare gases have revealed the presence of both copious harmonic production and fluorescence. The highest harmonic observed was the seventeenth (14.6 nm) in Ne, the shortest wavelength ever produced by that means. Strong fluorescence was seen in Ar, Kr, and Xe with the shortest wavelengths observed being below 10 nm. Furthermore, radiation from inner-shell excited configurations in Xe, specifically the 4d9 5s5p → 4d10 5s manifold at ~ 17.7 nm, was detected. The behaviors of the rare gases with respect to multiquantum ionization, harmonic production, and fluorescence were found to be correlated so that the materials fell into two groups, He and Ne in one and Ar, Kr, and Xe in the other. These experimental findings, in alliance with other studies on innershell decay processes, give evidence for a role of atomic correlations in a direct nonlinear process of inner-shell excitation. It is expected that an understanding of these high-field processes will enable the generation of stimulated emission in the x-ray range.

Cubic nonlinear optical effects in conjugated polymers.

Abstract: A general survey of harmonic generation techniques in polymer thin film is given and some recent results of wave dispersed third harmonic generation measurements on conjugated polymers with one dimensional π-electron delocalization are reviewed and discussed. These polymers exhibit very large cubic hyperpolarizabilities in near infrared. Some multiphoton (two and three photon) resonance enhancements in cubic susceptibility are observed. The two photon level with the same symmetry as the fundamental one lies in studied polymers below the allowed for optical transition one photon level. Possible practical applications of observed resonances are discussed.

Efficient generation of the second harmonic of a nanosecond CO2 laser radiation pulse

Abstract: Efficient (49 ± 5%) second harmonic generation was demonstrated for the first time in the infrared. The frequency of CO2 laser radiation with a pulse duration of ~2 nsec and an intensity of up to 1GW/cm2 was doubled in an unbleached ZnGeP2 crystal. The internal energy efficiency was ~80%.

Three-dimensional nonlinear analysis of free-electron-laser amplifiers with planar wigglers.

Abstract: The nonlinear evolution of the free-electron-laser (FEL) amplifier is investigated numerically for a configuration consisting of a planar wiggler with parabolically tapered pole pieces. A set of coupled nonlinear differential equations is derived in three dimensions which governs the self-consistent evolution of the TE and TM modes in a loss-free rectangular waveguide as well as the trajectories of an ensemble of electrons. The initial conditions are chosen to model the injection of a cylindrically symmetric electron beam into the wiggler by means of a region with an adiabatically tapered wiggler amplitude, and the effect of an initial beam momentum spread is included in the formulation. Both self-field and space-charge effects have been neglected, and the analysis is valid for the high-gain Compton regime. In addition, the phase stability of the FEL amplifier against fluctuations in the beam voltage, the enhancement of the efficiency by means of a tapered wiggler amplitude, and harmonic generation are also studied. Numerical simulations are conducted to model a 35-GHz amplifier with an electron beam energy of 3.5 MeV, and good agreement is found between the simulation and an experiment conducted by Orzechowski and co-workers. Significantly, the results indicate that a tapered wiggler configuration is somewhat less sensitive to the beam thermal spread than a uniform wiggler system.

Generation of the ninth, eleventh, and fifteenth harmonics of iodine laser radiation

Abstract: Results of experiments to produce coherent radiation in the vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) by high‐order optical nonlinearities in rare gases are described. Frequency conversion into the third and fifth harmonics was used to obtain pulses at 146.1 and 87.7 nm. VUV pulses at 146.1 and 119.6 nm were directly generated from infrared radiation by generating the ninth and eleventh harmonics of 1.315‐μm iodine laser pulses. Frequency conversion into the eleventh harmonic is the highest‐order nonlinear process of this kind reported to date.

Second-harmonic generation of a continuous-wave diode-pumped Nd:YAG laser using an externally resonant cavity

Abstract: We report 13% second-harmonic conversion efficiency of a 15-mW, cw, diode-laser-pumped Nd:YAG oscillator. 2 mW of single-axial-mode 532-mm radiation was generated by externally resonant second-harmonic generation in a monolithic MgO:LiNbO(3) nonlinear crystal cavity. The measured finesse of 450 for the monolithic external cavity indicated that absorption and scatter losses in the doubler were less than 0.8%.

Noncritically phase‐matched sum frequency generation and image up‐conversion in KNbO3 crystals

Abstract: Tunable and continuous wave (cw) near infrared up‐conversion into the dark blue wavelength range (410–465 nm) has been achieved in KNbO3 crystals using the nonlinear optical coefficient d32 (ω1+ω2; ω1,ω2)=20.4 pm/V. High efficiencies have been reached due to the large nonlinearity and the possibility of temperature‐tuned noncritical 90° phase matching. Using a neodymium:yttrium aluminum garnet laser (1064.2 nm) as the signal source and a krypton laser (676.4 nm) as the pump source, a sum signal (413.6 nm) power of over 0.1 mW was reached at a pump power of only 26.2 mW. cw image up‐conversion into the blue wavelength range has been demonstrated using a noncritically phase‐matched configuration in the same crystals at T=−4 °C.

Low-threshold synchronously pumped all-fiber ring Raman laser

Abstract: Experimental results on a synchronously pumped, all single-mode fiber Raman laser with a low threshold of 740 mW are reported. Suppression of gain fluctuations due to pump phase noise has been achieved by implementing a fiber coupler of high multiplexing effect. Multistokes generation of low-noise optical pulse trains at \lambda = 1.12 \mu m and \lambda = 1.18 \mu m has also been obtained with a subwatt pump threshold.

Nuclear motion and electric hyperpolarizabilities

Abstract: Formulas are given for the vibrational components of the static and dynamic electric hyperpolarizabilities β and γ. Some previous inconsistencies in the literature are pointed out.

Direct measurement of effective indices of guided modes in LiNbO(3) waveguides using the Cerenkov second harmonic.

Abstract: Second-harmonic generation in the form of Cerenkov radiation has been used to make direct, contact-free measurements of the effective indices of guided modes in LiNbO(3) channel waveguides. X-cut substrates were used, and channels oriented along the y axis were formed by either proton exchange or titanium indiffusion. For end-fire TE excitation, the Cerenkov harmonic radiates forward at a shallow angle into the substrate, leaves the output facet of the substrate, and appears as bright bands in the far field. These bands are seen to form a one-to-one correspondence with the m lines that are due to guided modes when a prism coupler is simultaneously clamped to the sample surface. The effective indices of the guided modes can be obtained by a simple calculation that involves only the substrate index and the angle at which the Cerenkov harmonic is radiated into the substrate. This technique permits effective index measurements of cladded waveguides where prism coupler measurements cannot be made. Examples of the technique in which index oil is used as a guide overlayer are given.

Second-harmonic generation in a multimode laser cavity

Abstract: We present a theoretical study of a multilongitudinal-mode laser with an intracavity-doubling crystal. The longitudinal modes are coupled to one another through frequency-doubling processes (because of the crystal) and through sum-frequency processes (because of the laser cavity). This leads to a mode–mode competition that significantly alters the nature of the output solutions.

Harmonic generation in free-electron lasers

Abstract: : A nonlinear formulation of the free-electron-laser amplifier with a linearly polarized wiggler magnetic field is used to study harmonic generation. Substantial emission is found to occur at the harmonics for a cold beam; however, the harmonics are far more sensitive to beam thermal effects than is the fundamental. Reprints. (rh)

Optical harmonic generation in nonuniform gaseous media with application to frequency tripling in free-jet expansions

Abstract: We consider the process of optical harmonic generation in systems with arbitrary gas density variation along the optical beam and specifically consider the case of frequency tripling in a free-jet expansion. Generalized relationships are presented for harmonic conversion efficiency as a function of the shape of the density profile and of the focusing conditions. For the case of frequency tripling, we have examined these effects numerically and find that the maximum attainable third-harmonic power is relatively insensitive to the form of this profile for negatively dispersing gases, but is quite sensitive to the profile in the case of positive dispersion. We also find that for a given confocal parameter b the maximum attainable conversion efficiency is surprisingly insensitive to the effective cell length L and depends on b and L only through the factor 16\beta/b^{2} where β is a relatively weak function of the ratio b/L , ranging from 1 to 4 for the case of negative dispersion and from 0 to 1 for the case of positive dispersion. The specific case of frequency tripling in a free-jet expansion is modeled, and stategies for power optimization are discussed.

Heterodyne detection of tunable FIR sidebands

Abstract: Continuously tunable far infrared (FIR) laser sidebands have been generated in a Schottky diode by nonlinear mixing the radiation from an optically pumped FIR laser operating between 0.6 and 3 THz with that from a microwave source in the 2-4 GHz range. A very sensitive heterodyne detection is adapted to detect the sidebands generated not only at the sum or difference frequency of the two radiations, but also, for the first time in the FIR region, those related to the mixing of the FIR radiation with the second and third harmonics of the microwaves. The high selectivity of the superheterodyne detection allows easy separation of the various sidebands. The global tunability of this system is 2 × 10 GHz for the more powerful FIR emission lines. To demonstrate the tunability of the device absorption signals of several molecules are presented in the whole range of operation of the system (0.6-3 THz) using either direct or lock-in detection techniques.

Multiphoton ionization spectra and tunable fifth-harmonic production near five-photon resonances in Xe and Ar.

Abstract: Through multiphoton ionization measurements, we have observed the interference of five-photon and internally generated fifth-harmonic excitation processes in ..delta..J = 1 even-odd parity resonant transitions in Xe and Ar. In agreement with theory, these five-photon resonances are not observable in single-pass laser beams, but are convincingly observed in counterpropagating beams. In the negatively dispersive regions of the 5d(3/2)/sup 0/J = 1 level of Xe, tunable fifth-harmonic light is generated by phase matching with various buffer-gas mixtures. The fifth-harmonic profiles are in good agreement with calculated phase-matching curves.

Topics on nonlinear wave-plasma interaction

Abstract: General References.- I Basic equations.- 1 Hydrodynamic plasma description.- 2 Basic equations for high-frequency processes.- 3 Basic equations for low-frequency processes.- References.- II Elements of linear wave propagation.- 4 Linear wave propagation in plasmas.- 4.1 Linear wave equation.- 4.2 Penetration of a plasma by an electromagnetic wave.- 4.3 Resonance absorption.- References.- 5 Structure resonances.- 5.1 Resonances at s-polarization.- 5.2 Surface wave resonances.- 5.3 Electrostatic structure resonances.- References.- III High-frequency nonlinear processes.- 6 Harmonic generation.- 6.1 Calculation of nonlinear source terms.- 6.2 Linear density profile.- 6.3 Non-monotoneous density profiles.- 6.4 Harmonic generation by anharmonic electron motion.- 6. 5 Self-interaction of transverse waves in a homogeneous plasma.- References.- 7 Stimulated Raman scattering (SRS) and two-plasmon- decay (TPD).- 7.1 Parametric instabilities and three-wave coupling.- 7.2 SRS and TPD in a homogeneous plasma.- 7.3 SRS and TPD in an inhomogeneous plasma.- 7.4 Mode coupling equations for SRS and TPD in an inhomogeneous plasma.- 7.5 Results of mode coupling analysis of SRS, TPD.- 7.6 Odd-integer half-harmonic radiation.- References.- IV Low-frequency nonlinear processes.- 8 Linearized plasma dynamics.- 8.1 Ion acoustic waves.- 8.2 Zakharov system, nonlinear Schrodinger equation.- References.- 9 Stimulated Mandelstam-Brillouin scattering (SBS).- 9.1 SBS in a homogeneous infinite plasma (temporal problem).- 9.2 Space-time development of SBS in a plasma of finite length.- 9.3 SBS as steady-state spatial problem.- 9.4 Convective SBS instability.- 9.5 Brillouin backscatter pulsations.- 9.6 Strong-coupling effects.- 9.7 SBS saturation by ion acoustic nonlinearities.- 9.8 The influence of plasma flow on SBS.- References.- 10 Strongly nonlinear stationary waves.- 0.1 Basic equations.- 0.2 Equilibrium states (envelope solitions, nonlinear skin effect).- 10.3 Nonlinear stationary waves with plasma flow.- 10.4 Double-humped solitons, shock-like structures.- References.- 11 Strongly nonlinear instationary interaction.- 11.1 Profile deformation at resonance absorption.- 11.2 Nonlinear stage of stimulated Mandelstam-Brillouin scattering.- 11.3 Superreflection.- 11.4 Nonstationary skin-effect plasma acceleration plasma confinement.- References.- References.

Multiple layer optical memory system using second-harmonic-generation readout

Abstract: A novel optical read and write information storage system is described which comprises a radiation source such as a laser for writing and illumination, the radiation source being capable of radiating a preselected first frequency; a storage medium including at least one layer of material for receiving radiation from the radiation source and capable of being surface modified in response to said radiation source when operated in a writing mode and capable of generating a pattern of radiation of the second harmonic of the preselected frequency when illuminated by the radiation source at the preselected frequency corresponding to the surface modifications on the storage medium; and a detector to receive the pattern of second harmonic frequency generated.

Second-harmonic generation in amorphous vinylidene cyanide/vinyl acetate copolymer using a pulsed Nd:YAG laser.

Abstract: Second-harmonic generation was recently observed in an amorphous vinylidene cyanide/vinyl acetate copolymer film by using a pulsed Nd:YAG 1.06-μm laser.