Sub-6-fs blue pulses generated by quasi-phase-matching second-harmonic generation pulse compression

Abstract. : We demonstrate a novel scalable and engineerable approach for the frequency-doubling of ultrashort pulses. Our technique is based on quasi-phase-matching and simultaneously provides tailored dispersion and nonlinear frequency conversion of few-cycle optical pulses. The method makes use of the spatial localization of the conversion process and the group velocity mismatch in a chirped grating structure. The total group delay of the nonlinear device can be designed to generate nearly arbitrarily chirped second-harmonic pulses from positively or negatively chirped input pulses. In particular, compressed second-harmonic pulses can be obtained. A brief summary of the underlying theory is presented, followed by a detailed discussion of our experimental results. We experimentally demonstrate quasi-phase-matching pulse compression in the sub-10-fs regime by generating few-cycle pulses in the blue to near-ultraviolet spectral range. Using this new frequency conversion technique, we generate sub-6-fs pulses centered at 405nm by second-harmonic generation from a 8.6fs Ti:sapphire laser pulse. The generated spectrum spans a bandwidth of 220THz. To our knowledge, these are the shortest pulses ever obtained by second-harmonic generatio

Dispersive properties of quasi-phase-matched optical parametric amplifiers

The dispersive properties of non-degenerate optical parametric amplification in quasi-phase-matched (QPM) nonlinear quadratic crystals with an arbitrary grating profile are theoretically investigated in the no-pump-depletion limit. The spectral group delay curve of the amplifier is shown to be univocally determined by its spectral power gain curve through a Hilbert transform. Such a constraint has important implications on the propagation of spectrally-narrow optical pulses through the amplifier. In particular, it is shown that anomalous transit times, corresponding to superluminal or even negative group velocities, are possible near local minima of the spectral gain curve. A possible experimental observation of such effects using a QPM Lithium-Niobate crystal is suggested.Comment: submitted for publicatio

Engineered optical nonlinearity for a quantum light source

Single-photon pairs created in the nonlinear process of spontaneous parametric downconversion form the backbone of fundamental and applied experimental quantum information science. Many applications benefit from careful spectral shaping of the single-photon wave-packets. In this paper we tailor the joint spectral wave-function of downconverted photons by modulating the nonlinearity of a poled crystal without affecting the phase-matching conditions. We designed a crystal with a Gaussian nonlinearity profile and confirmed successful wave-packet shaping by two-photon interference experiments. We numerically show how our method can be applied for attaining one of the currently most important goals of single-photon quantum optics, the creation of pure single photons without spectral correlations.Comment: 7 pages (4 pages + appendices), 5 figures. Minor formatting changes. Fixed typos. Some additional reference

Wave-front engineering by Huygens-Fresnel principle for nonlinear optical interactions in domain engineered structures

The wave-front engineering for nonlinear optical interactions was discussed. Using Huygens-Fresnel principle we developed a general theory and technique for domain engineering with conventional quasi-phase-matching structures being the special cases. By Fourier analysis we put forward the concept of local quasi-phase matching, which suggests that the quasi-phase matching is fulfilled only locally not globally. Experiments on focal effect of second-harmonic wave agreed well with the theoretical prediction. The proposed scheme combines three optical functions: generation, focusing and beam splitting of second-harmonic wave, thus making the device more compact. Further the proposed scheme can be used to perform the integration of multi-functional optical properties in nonlinear photonics, as well as expand the use of nonlinear optical devices.Comment: 15 pages, 3 figure

Difference-frequency generation with quantum-limited efficiency in triply-resonant nonlinear cavities

We present a comprehensive study of second-order nonlinear difference frequency generation in triply resonant cavities using a theoretical framework based on coupled-mode theory. We show that optimal quantum-limited conversion efficiency can be achieved at any pump power when the powers at the pump and idler frequencies satisfy a critical relationship. We demonstrate the existence of a broad parameter range in which all triply-resonant DFG processes exhibit monostable conversion. We also demonstrate the existence of a geometry-dependent bistable region.Comment: 10 pages, 3 figure

Efficient Terahertz Generation in Triply Resonant Nonlinear Photonic Crystal Microcavities

We propose a scheme for efficient cavity-enhanced nonlinear THz generation via difference-frequency generation (DFG) processes using a triply resonant system based on photonic crystal cavities. We show that high nonlinear overlap can be achieved by coupling a THz cavity to a doubly-resonant, dual-polarization near-infrared (e.g. telecom band) photonic-crystal nanobeam cavity, allowing the mixing of three mutually orthogonal fundamental cavity modes through a chi(2) nonlinearity. We demonstrate through coupled-mode theory that complete depletion of the pump frequency - i.e., quantum-limited conversion - is possible in an experimentally feasible geometry, with the operating output power at the point of optimal total conversion efficiency adjustable by varying the mode quality (Q) factors.Comment: 8 pages, 3 figure

Engineered nonlinear lattices

We show that with the quasi-phase-matching technique it is possible to fabricate stripes of nonlinearity that trap and guide light like waveguides. We investigate an array of such stripes and find that when the stripes are sufficiently narrow, the beam dynamics is governed by a quadratic nonlinear discrete equation. The proposed structure therefore provides an experimental setting for exploring discrete effects in a controlled manner. In particular, we show propagation of breathers that are eventually trapped by discreteness. When the stripes are wide the beams evolve in a structure we term a quasilattice, which interpolates between a lattice system and a continuous system.Peer ReviewedPostprint (published version

Entangled-Photon Generation from Parametric Down-Conversion in Media with Inhomogeneous Nonlinearity

We develop and experimentally verify a theory of Type-II spontaneous parametric down-conversion (SPDC) in media with inhomogeneous distributions of second-order nonlinearity. As a special case, we explore interference effects from SPDC generated in a cascade of two bulk crystals separated by an air gap. The polarization quantum-interference pattern is found to vary strongly with the spacing between the two crystals. This is found to be a cooperative effect due to two mechanisms: the chromatic dispersion of the medium separating the crystals and spatiotemporal effects which arise from the inclusion of transverse wave vectors. These effects provide two concomitant avenues for controlling the quantum state generated in SPDC. We expect these results to be of interest for the development of quantum technologies and the generation of SPDC in periodically varying nonlinear materials.Comment: submitted to Physical Review

Generation of dual-wavelength pulses by frequency doubling with quasi-phase-matching gratings

We demonstrate generation of two synchronized picosecond pulses at different wavelengths near 778 nm by frequency doubling of a femtosecond pulse. We use nonlinear frequency filtering with quasi-phase-matching gratings, which allow us to obtain second-harmonic spectral intensities that are higher than the spectral intensities of the pump. © 2001 Optical Society of America OCIS codes: 140.7090, 190.7110, 190.2620, 320.5540, 320.7110. Synchronized short pulses generated at two different wavelengths are required in such applications as pump -probe experiments, coherent control, and generation of short pulses in the mid infrared by difference-frequency generation. Over the past several years a number of dual-wavelength Ti:sapphire oscillators have been demonstrated that use relatively complex dual-cavity designs to eliminate timing jitter between the pulses. -4 Another approach to the generation of dual-wavelength pulses is to use linear frequency f iltering of a single pulse. 9,10 Here we use this QPM SHG pulse-shaping technique to demonstrate generation of synchronized dual-wavelength pulses. Using structures with a phase-reversal sequence superimposed upon a uniform grating, we produce two synchronized coherent picosecond pulses by QPM SHG spectral filtering of a single femtosecond FH pulse. The wavelengths of the secondharmonic (SH) pulses and their temporal lengths are determined by the grating design, subject to limitation by the bandwidth of the FH pulse. Because of the nonlinear nature of QPM SHG filtering, the energy efficiency is not limited by the passband of the filter and, in fact, the SH spectral intensity can exceed the FH spectral intensity over the same bandwidth. We note that QPM devices similar to those described here have already been used for a cw frequency conversion. 11 Under the assumptions of plane-wave interaction, an undepleted pump, slowly varying envelopes, and negligible group velocity and higher-order dispersion of the material, the QPM SHG process is described with a transfer-function relation 9,10 : where 2 ͑V͒ is the frequency-domain envelope of the output SH and d A 1 2 ͑V͒ is the self-convolution of the frequency-domain envelope of the input FH and hence is proportional to the spectrum of the nonlinear drive. In Eq. where g ϵ 2p͞l 1 n 2 , l 1 is the FH wavelength, and n 2 is the SH refractive index. In Eq. (2) Dk 0 2k 1 2 k 2 and dv 1͞u 1 2 1͞u 2 , where k i are the carrier k vectors and u i ͑dk͞dv͒ 21 j vvi are the group velocities for the FH ͑i 1͒ and the SH ͑i 2͒. We first consider a constant-duty-cycle uniform QPM grating of length L and period L 0 (and hence the grating k vector for first-order QPM K 0 2p͞L 0 ). Ultrashort-pulse SHG with such gratings was previously analyzed in the literature where jdj is related to the intrinsic nonlinear coefficient of the material, d eff , as jdj ͑2͞p͒d eff for firstorder QPM; we also assume that the QPM condition is satisfied: K 0 Dk 0 . Equation (3) gives a familiar sinc 2 tuning curve when jD 0 ͑V͒j 2 is evaluated. The tuning curve is centered at V 0 and has a FWHM of DV 0 5.57͑͞dvL͒, which, for a given dv (material parameter), is determined by the grating length. If the width ofD 0 ͑V͒ is much smaller than the bandwidth of the nonlinear drive d A 1 2 ͑V͒, DV, the spectrum of the generated SH essentially replicatesD 0 ͑V͒; hence in the time domain the SH is a long (compared with the FH) top-hat pulse of length dvL [se

Sub-6-fs blue pulses generated by quasi-phase-matching second-harmonic generation pulse compression

ISSN:0946-2171ISSN:1432-0649ISSN:0721-7269ISSN:0340-379