Harmonic Generation Of Light Research Articles

Intracavity noncollinear second harmonic generation of Nd-YAG laser light

Noncollinear second harmonic generation was demonstrated on a specially shaped LiIO 3 crystal, placed inside the closed cavity of a Q-switched Nd-YAG laser. The second harmonic light is emitted from the resonator in an out-of-axis direction with an extremely low divergence as long as the fundamental laser light totally remains inside the cavity.

Coherent sources of extreme uv

Light sources in the extreme ultraviolet wavelength regime—from 104 nanometers down to the start of the x‐ray region at about 10 nm—are of particular interest for molecular spectroscopy and solid‐state surface studies. But this xuv domain poses special difficulties. The beams must be propagated in vacuum, but at these wavelengths there are no longer any solid materials available for vacuum windows or the harmonic generation of xuv light from longer wavelength sources. Crystalline lithium flouride, the last of the solids to maintain its transparency in the ultraviolet, becomes completely opaque at 104 nm. Beams of xuv can of course be generated by synchrotron light sources, but their usefulness is limited: The synchrotron beams do not provide coherent xuv light. Their spectral brightness (power per unit wavelength interval) is at present marginal for high‐resolution molecular spectroscopy. Furthermore, synchrotron beams are available only at large storage‐ring facilities; they cannot be brought into the experimenter's home laboratory.

THE SECOND HARMONIC GENERATION IN LiNbO3 CRYSTALS WITH PERIODIC LAMINAR FERROELECTRIC DOMAINS

We studied the second harmonic generation of light in LiNbO3 crystals with periodic laminar ferroelectric domains, in order to make a detailed experimental verification of the theory of quasi-phase-matching proposed by N. Bloembergen et al. First we determined the second harmonic light intensity of single domain LiNbO3 crystals in the regime eω ·eωe→e2ω. Then by using angle-scanning and temperature-scanning, we obtained the maximum second harmonic output from crystals with periodic domains corresponding to quasi-phase-matching. We have verified experimentally the relation that the second harmonic output is proportional to N2(N is the number of domains in the crystal) with N up to 200. We have compared the second harmonic output of crystals with periodic laminar domains in the quasi-phase-matching regime with that of single domain crystals of the same length and optical quality under phase-matched condition oω· oω→e2ω. An order of magnitude enhancement of second harmonic light output has been found. Finally, the structure sensitivity of the second harmonic generation of LiNbO3 crystal with periodic laminar ferroelectric domains has also been studied experimentally.

Second harmonic light generation in the rabbit cornea

The conversion efficiency for second harmonic generation of light in a rabbit cornea from a pulsed YAG laser has been measured to be 6 x 10(-9) for an input power density of 1 MW/cm(2). Because of this low efficiency it does not seem likely that second harmonic energy generated in the corena could cause retinal damage. These results do not rule out the possibility that there is a similar effect occurring in the retina.

Nonlinear optical interferometer

The interferometer described, based on the second harmonic generation of light, is useful in the contouring of refractive objects with large variations in optical depth. The device is a real-time common-path self-referencing interferometer that yields interferograms in the visible with an equivalent wavelength of the order of 50 microm. We describe experiments that show that it can serve as a useful device. The key to the device is the use of Y-cut LiNbO(3) configured for surface acoustooptic applications rather than for conventional second harmonic applications. The crystals are noncritically phase matched by temperature control and are used with a repetitively pulsed Nd:YAG laser operating at 1.06 microm.

Second-harmonic interferometers II

Experiments on interferometers based on second harmonic generation of light are described. These make use of the distortions of phase and amplitude produced by the phase mismatch of angle-matched crystals to provide information. The interferometers are directly sensitive to small wavefront tilts and do not require additional reference wavefronts.

Field analysis of harmonic generation in thin-film integrated optics

Harmonic generation of light in thin-film optical waveguides is analyzed theoretically by evaluating the total electromagnetic fields that satisfy the polarization driven wave equation and the electromagnetic boundary conditions at both interfaces. Analytical expressions are given for the amplitude of the growing wave component of the total fields. The results agree with those of normal mode analysis only in the limit of phase-matched harmonic generation. This analysis is believed to be applicable to a large range of wave interaction phenomena in integrated optics.

Second harmonic measurement of the order parameter variation near the multicritical point of NH4Cl

Pressure variations of the order parameter η of NH4Cl are measured by second harmonic generation of light. The transition is continuous above 1.5 kbar; below, a phase coexistence is observed which may induce plastic deformations. Possible interpretations of the data with critical exponents and with the Landau theory are discussed.

Optical second harmonic generation with surface plasmons in piezoelectric crystals

We report the first observation of reflected optical second harmonic generation of light due to excitation of fundamental and harmonic surface plasmon modes at the interface between a metallic film and a piezoelectric crystal. Excitation of the fundamental surface plasmon mode produces a large enhancement of the piezoelectric generated reflected harmonic light whereas excitation of the nonlinear mode produces only a small minimum in the background surface generated harmonic light.

Optical study of the α-β transition of quartz

Measurements of birefringence, light scattering, second harmonic light generation and scattering have been made simultaneously at the α-β transition of quartz. They have been correlated with a coexistence zone (observed visually) of α and β phases in the hysteresis region and with Dauphine twinning.

Second harmonic light generation in a nonlinear medium with random nonuniformities

Second harmonic light generation in a nonlinear medium with random nonuniformities

Double Refraction on Optical Second Harmonic in Thin Crystals

THE first observations of second harmonic generation of light (SHG) were made with a high-power pulsed ruby laser. Since then these nonlinear effects have been successfully observed with continuous wave He–Ne gas lasers1. Recently, the so-called aperture effect of SHG, which had been predicted2 and which is equivalent to the familiar phenomenon of double refraction, was experimentally observed3 in long crystals (of length 5 to 10 cm). We report here that SHG double refraction has been detected in thin crystals 1 mm to 2 mm thick, using as an input beam the light from a gas laser.

On the Origin of Second Harmonic Generation of Light in Liquid Crystals

Second Harmonic Generation of light (SHG) is used as a probe to study the structure of the nematic, cholesteric or smectic mesophases of various liquid crystals, with non centro-symmetric molecules. In one case (cholesteryl 2-(2-ethoxy ethoxy) ethyl carbonate) where SHG has already been reported, it is shown that SHG occurs in the crystalline rather than the mesomorphic phase. In all cases, no evidence is found of any SHG in any mesophase. Consequently, these are probably centrosymmetric by compensation, as is the normal liquid phase.

Total reflection in second harmonic generation of light

Total reflection in second harmonic generation of light

5A5 - The second harmonic generation of light by focused laser beams

An experimental and theoretical study is reported on second-harmonic generation (SHG) by focused laser beams in nonlinear crystals which are large compared to the extent of the focus. The gas laser beam is in the lowest order (Gaussian) mode and very close to index-matching conditions in the crystal. The intensity pattern of the SHG observed photographically has roughly the shape of a half moon with a very sharp edge. Fine structure has been observed consisting of a series of fringes extending from the edge into the bright region. The power has also been measured as a function of crystal orientation, and the position of the edge has been determined for the orientation giving maximum power. The theoretical treatment of the problem is based upon an exact formula for the second-harmonic field for the case in which the laser beam is in a Gaussian mode. A detailed analysis of the experimental data is presented which shows the theory to be in quantitative as well as qualitative agreement with experiment.

Optical harmonic generation and mixing of Raman laser light in nonlinear dielectric media

Optical harmonic generation and mixing of Raman laser light in nonlinear dielectric media

Wave propagation in nonlinear electromagnetic media

This brief tutorial review first discusses the physical origin of nonlinear electric and magnetic susceptibilities of electro-magnetic media, from the audio through the microwave to the visible range of the electromagnetic spectrum. Wave propagation in non-linear media can be described by a combination of Maxwell's equations and the nonlinear constitutive equations. The Manley-Rowe relationships are verified for anisotropic lossless dielectrica. Microwave harmonic generation in ferrites and other materials, microwave modulation of light, light harmonic generation, light mixing and parametric conversion are all discussed from a general common viewpoint. The boundary conditions at the surface of a nonlinear medium lead to generalizations of the laws of reflection and refraction of light.

Theory of Second Harmonic Generation of Light

A theory is given for the generation of second harmonic light in crystals analogous to the classical theory of crystal optics. Optical activity and absorption are neglected, but the anisotropy is treated rigorously. An approximate treatment is also given, valid for most crystals, which retains the essential effects of the anisotropy and neglects the minor effects. All coherence effects are treated exactly, and special attention is given to the case of index matching. An exact solution is given for the second harmonic waves produced in and outside the medium when the fundamental beam enters the medium at a plane surface. A brief discussion is given of the effects of the finite aperture of the beam. The theory is applied to recent experiments on KDP and quartz, and values are given for the second-order polarization coefficients of these materials. Finally, the theory is given for second harmonic generation by focused beams based upon the diffraction theory of an ideal focus.

Nonlinear Dielectric Polarization in Optical Media

The physical mechanisms which can produce second-order dielectric polarization are discussed on the basis of a simple extension of the theory of dispersion in ionic crystals. Four distinct mechanisms are described, three of which are related to the anharmonicity, second-order moment, and Raman scattering of the lattice. These mechanisms are strongly frequency dependent, since they involve ionic motions with resonant frequencies lower than the light frequency. The other mechanism is related to electronic processes of higher frequency than the light, and, therefore, is essentially flat in the range of the frequencies of optical masers. Since this range lies an order of magnitude higher than the ionic resonances, the fourth mechanism may be the dominant one. On the other hand, a consideration of the linear electro-optic effect shows that the lattice is strongly involved in this effect, and, therefore, may be very much less linear than the electrons. It is shown that the question of the mechanism involved in the second harmonic generation of light from strong laser beams may be settled by experiments which test the symmetry of the effect. The electronic mechanism is subject to further symmetry requirements beyond those for piezoelectric coefficients. In many cases, this would greatly reduce the number of independent constants describing the effect. In particular, for quartz and KDP there would be a single constant.