Kerr Gate Research Articles

Microscopic Imaging Through a Turbid Medium by Use of a Differential Optical Kerr Gate

Microscopic imaging of hidden objects in scattering media is demonstrated using a differential optical Kerr gate (DOKG). The results show that the high spatial frequency components of the imaged object filtered by the optical Kerr gate can be considerably compensated using the DOKG. Microscopic images with a maximal lateral resolution of $\sim 2$ - $\mu \text{m}$ can be achieved. Compared with OKG microscopic imaging, the contrast of DOKG microscopic images is enhanced significantly.

SiO_2-Al_2O_3-La_2O_3 glass - a superior medium for optical Kerr gating at moderate pump intensity

Novel SiO2-Al2O3-La2O3 (SAL) glass shows a switching efficiency η ≤ 70% for dual wavelengths optical Kerr gating (OKG) at 0.7 TW/cm2 peak intensity IP of the gate pulse. It steadily increases with IP, is highest for the highest La2O3 content (24 mol%) and then superior to OKG media of large nonlinear refractive index n2 above 150 GW/cm2 (ZnS), 350 GW/cm2 (tellurite glass), and 450 GW/cm2 (N-SF56 glass). This superiority is attributed to negligible nonlinear counter processes in SAL glass which in the large n2 valued media make η(IP) decrease in the high IP region.

Ultrafast Photoluminescence from the Core and the Shell in CdSe/CdS Dot-in-Rod Heterostructures.

With an ultrafast time-resolved photoluminescence system utilizing a Kerr gate, the time-resolved photoluminescence of core and shell constituents within CdSe/CdS dot-in-rod heterostructures is studied as a function of heterostructure size. Measurements performed at low excitation fluence generating, on average, less than one exciton per nanorod, reveal photoluminescence from direct recombination of carriers in the CdS heterostructure rod with lifetime generally increasing from 0.4 ps to 1.3 ps as the rod length increases. Decay of the CdS rod photoluminescence is accompanied by an increase in emission from the CdSe core on comparable time scales, also trending towards larger values as the rod length increases. The observed kinetics can be explained without invoking a non-radiative trapping mechanism. We also present alloying as a mechanism for enhancing electron confinement and reducing fluorescence lifetime at nanosecond time scales.

Ultrafast optical Kerr gate imaging in a poly-disperse turbid medium

The influence of the size parameter of the scatterers on ultrafast optical Kerr gate (OKG) imaging is investigated in highly scattering poly-disperse turbid media. The results show that in a poly-disperse turbid medium, which in our case, is a suspension of two different sized mono-disperse microspheres, the temporal and spatial behaviors of the light pulses transmitted through it are dominated by the smaller microspheres. The contrasts of the OKG images for the poly-disperse microsphere sample are closer to the contrasts of the OKG images for the smaller sized mono-disperse microsphere sample.

Mechano-optical transmittance and third order nonlinear optical properties exhibited by Au nanoparticles

Acceleration and velocity of Au nanoparticles suspended in ethanol were evaluated by considering optical transmittance experiments as a function of time. The evolution of the third order nonlinear optical characteristics of the sample was examined by a two-wave mixing technique at 532nm wavelength with nanosecond pulses. The dynamical position and the nonlinear optical properties of the studied nanogold showed a strong dependence on nanoparticle size; besides an exponential behavior due to intermolecular interactions was estimated. A time-resolved mechano-optical effect was experimentally observed by a nanosecond optical Kerr gate configuration. Atomic Force Microscopy studies in a dielectric thin film sample prepared with the nanoparticles by a sol–gel processing route were conducted to determine the nanoparticles size distribution. Micrographic analysis pointed out that the explored nanoparticles size is between 65 and 155nm with an average size of 98nm. Potential applications for developing mechano-optical operations capable to modulate optical signals dependent on time were contemplated.

ChemInform Abstract: Excitation Wavelength Dependence of the Solvation Dynamics of 4′‐N,N‐Diethylamino‐3‐methoxyflavon in Ionic Liquids

AbstractReview: 21 refs.

Real-time observation of phonon-polariton dynamics in ferroelectric LiNbO3 in time-frequency space

We demonstrate the real-time observation of phonon-polariton propagation in ferroelectric LiNbO3 using a single-shot spectroscopic setup that employs an echelon mirror. The echelon mirror provides a spatially encoded time delay for the probe pulse; therefore, the ultrafast transient behavior of materials can be detected on a single-shot basis. Using optical Kerr gate apparatus, forward and backward propagating E-mode phonon-polaritons were simultaneously induced via an impulsive stimulated Raman scattering process, and subsequently, their dynamics were readily mapped in time-frequency space using heterodyne detection. The two phonon-polaritons appeared on opposite sides of the central probe wavelength and were symmetrically imaged against the ordinary and extraordinary probe lights. By taking into account coupling of the lowest E-mode phonon-polariton to a low-frequency relaxational mode, not only the phonon-polariton dispersion but also the wavevector dependence of the damping rate was unveiled and quantitatively evaluated.

Excitation Wavelength Dependence of the Solvation Dynamics of 4′-N,N-Diethylamino-3-methoxyflavon in Ionic Liquids

Abstract Time-resolved fluorescence spectra of 4′-N,N-diethylamino-3-methoxyflavon in ionic liquids have been measured by using a Kerr gate method and a streak camera at different excitation wavelengths, 370, 400, and 425 nm. Fluorescence spectra showed a shift to longer wavelength with longer delay time after photoexcitation. The peak position of the fluorescence spectrum at each delay time was evaluated by simulating the spectrum by a log-normal function. It was found that the peak shift of the fluorescence at the early delay time was larger for the shorter excitation wavelength (blue side of the absorption), and in the longer delay time they coincide to the same value. The time profile of the peak position was well simulated by the sum of an exponential function and a stretched-exponential function. The average relaxation times evaluated by the integration of the longer relaxation function were weakly dependent on the excitation wavelength, and they were correlated with the viscosity of the solvent. The relation with the excitation wavelength dependence of the excited state intramolecular proton transfer reaction of 4′-N,N-diethylamino-3-hydroxyflavon is discussed.

Collective optical Kerr effect exhibited by an integrated configuration of silicon quantum dots and gold nanoparticles embedded in ion-implanted silica

The study of the third-order optical nonlinear response exhibited by a composite containing gold nanoparticles and silicon quantum dots nucleated by ion implantation in a high-purity silica matrix is presented. The nanocomposites were explored as an integrated configuration containing two different ion-implanted distributions. The time-resolved optical Kerr gate and z-scan techniques were conducted using 80 fs pulses at a 825 nm wavelength; while the nanosecond response was investigated by a vectorial two-wave mixing method at 532 nm with 1 ns pulses. An ultrafast purely electronic nonlinearity was associated to the optical Kerr effect for the femtosecond experiments, while a thermal effect was identified as the main mechanism responsible for the nonlinear optical refraction induced by nanosecond pulses. Comparative experimental tests for examining the contribution of the Au and Si distributions to the total third-order optical response were carried out. We consider that the additional defects generated by consecutive ion irradiations in the preparation of ion-implanted samples do not notably modify the off-resonance electronic optical nonlinearities; but they do result in an important change for near-resonant nanosecond third-order optical phenomena exhibited by the closely spaced nanoparticle distributions.

Pulse contrast improvement for chirped pulse amplification lasers by spectro-temporal filtering

A spectro-temporal filtering method is proposed to increase the contrast ratio of chirped pulses. The advantages of this method include easy cascading, high transmission, and it can also be used in the high-energy chirped pulse amplifier (CPA) system. The effectiveness of the proposed method was experimentally verified by operating the spectro-temporal filtering method on a Ti:sapphire CPA system and then measuring the contrast ratio of pulse based on optical Kerr gate effect(OKG). The measuring result demonstrated that, after passing through one-stage spectro-temporal filtering system with transmittance up to 70%, the contrast ratio of the pulse was improved by an order of magnitude.

Time-resolved fluorescence methods (IUPAC Technical Report)

Abstract This IUPAC Technical Report describes and compares the currently applied methods for measuring and analyzing time-resolved fluorescence traces using phase-modulation fluorometry as well as pulse fluorometry (direct emission decay measurements, single-photon timing, streak camera measurements, fluorescence upconversion, and optical Kerr gating). The paper starts with a brief description of the basic principles for time and frequency domain fluorescence spectroscopy. The fundamental equations are given, and recommendations for adequate use are emphasized. The up-to-date, commonly employed excitation sources and photodetectors are described in detail. The analysis of time-resolved fluorescence data is discussed. Attention is paid to possible artifacts, and remedies are presented on how to avoid them or to account for them. Finally, fluorescence lifetime standards for the nanosecond and picosecond timescales are collected.

Sharpness-enhanced ultrafast imaging by using a biased optical Kerr gate.

We proposed a novel biased optical Kerr gated imaging (BOKGI) method for ultrafast imaging. The imaging performance of the BOKGI system has been investigated. Experimental results showed that by using the BOKGI, the high spatial frequency components of the detected object could be effectively retrieved, which are often filtered by the photo-induced soft aperture in a conventional OKGI system. Comparing with the conventional OKGI method, the BOKGI method could enhance the sharpness of images and provide a higher spatial resolution of the imaging system. In addition, the influence of the biased angle on the BOKGI performance has been also investigated.

Comparative study of two ballistic imaging methods based on the femtosecond optical Kerr gate and spatial filtering

We demonstrated two ballistic imaging for an object hidden behind turbid media using the optical Kerr gate (OKG) and spatial filtering (SF), respectively. The influence of the scattering parameters of the turbid media on the image contrast was investigated. The experimental results showed that the image contrast of the SF imaging decreased significantly with increasing optical density and scattering particle size of the turbid media. Compared to the SF imaging, the OKG imaging showed a higher and more stable image contrast as scattering photons in the optical gated imaging case were more effectively eliminated.

Measurement of femtosecond pulse contrast of low-repetition-rate lasers by optical Kerr effect

In this paper, pulse contrast was measured for femtosecond lasers with low-repetition-rate (40 Hz) using optical Kerr gate as a sampler. The results show that, without attenuator, dynamic range as high as 104 was achieved, with a scanning range of 126 ps and a temporal sampling interval of 6.3 fs. Moreover, the method suits for measuring laser pulse contrast in wide spectrum range.

Ultrafast optical Kerr gate of bismuth–plumbum oxide glass for time-gated ballistic imaging

We demonstrated the time-gated ballistic imaging technique using a femtosecond optical Kerr gate (OKG) of bismuth–plumbum oxide glass, the nonlinear optical properties of which were also investigated. The third-order nonlinear refractive-index n2 of the bismuth–plumbum oxide glass was measured to be 2.19 × 10−15 cm2/W, and the nonlinear response time was estimated to be shorter than 180 fs. For the time-gated ballistic imaging, the maximum measurable optical density of turbid media using the OKG of bismuth–plumbum oxide glass was 9.3, while only 7.0 for the OKG of quartz glass. And the intensities of the images for the bismuth–plumbum oxide glass were approximately two orders of magnitude higher than that for the quartz glass. The experimental results indicated that the bismuth–plumbum oxide glass was an excellent optical material for nonlinear optical applications.

Collinear, two-color optical Kerr effect shutter for ultrafast time-resolved imaging.

Imaging with ultrashort exposure times is generally achieved with a crossed-beam geometry. In the usual arrangement, an off-axis gating pulse induces birefringence in a medium exhibiting a strong Kerr response (commonly carbon disulfide) which is followed by a polarizer aligned to fully attenuate the on-axis imaging beam. By properly timing the gate pulse, imaging light experiences a polarization change allowing time-dependent transmission through the polarizer to form an ultrashort image. The crossed-beam system is effective in generating short gate times, however, signal transmission through the system is complicated by the crossing angle of the gate and imaging beams. This work presents a robust ultrafast time-gated imaging scheme based on a combination of type-I frequency doubling and a collinear optical arrangement in carbon disulfide. We discuss spatial effects arising from crossed-beam Kerr gating, and examine the imaging spatial resolution and transmission timing affected by collinear activation of the Kerr medium, which eliminates crossing angle spatial effects and produces gate times on the order of 1 ps. In addition, the collinear, two-color system is applied to image structure in an optical fiber and a gasoline fuel spray, in order to demonstrate image formation utilizing ballistic or refracted light, selected on the basis of its transmission time.

Optical imaging of objects in turbid media using heterodyned optical Kerr gate

In this paper, we demonstrated optical imaging of objects hidden behind highly turbid media with a femtosecond heterodyned optical Kerr gate (HOKG). The experimental results showed that when compared with traditional optical Kerr gated (OKG) imaging, the HOKG imaging system provided higher image sharpness and higher spatial resolution. In traditional OKG imaging system, low pass filtering due to a photoinduced soft aperture decreased the image sharpness. When the HOKG was used, the high spatial frequency components of the object could be effectively compensated.

Near-infrared nonlinearity of a multicomponent tellurium oxide glass at 800 and 1,064 nm

We report on the nonlinear (NL) optical prop- erties of glassy TeO2-GeO2-K2O-Bi2O3 at k = 800 nm and k = 1,064 nm. Using the Kerr gate technique with a laser delivering 150 fs pulses at 800 nm, we demonstrated the fast NL response of the samples. The modulus of the NL refractive index, n2, at 800 nm was *10 -15 cm 2 /W. The Z-scan technique was used to determine n2 & ?10 -15 cm 2 /W, at 1,064 nm with pulses of 17 ps. The two-photon absorption coefficient, a2, was smaller than the minimum that we can measure (\0.003 cm/GW). The figure of merit n2/a2 k was calculated and indicates that this glass composition has large potential to be used for all-optical switching.

Enhanced broadband ultrafast detection of ultraviolet emission using optical Kerr gating.

We demonstrate a high-sensitivity ultrafast emission spectrometer based on the optical Kerr effect that time resolves emission simultaneously in the ultraviolet and visible ranges. We show that using benzene as the Kerr medium leads to the optimal balance between time-resolution and sensitivity of the optical shutter with low losses due to ultraviolet absorption. Using this medium together with high contrast broadband polarizers and charge-coupled device detection, we achieve efficient detection of emission transients (bandwidth >1.5 eV) in a time bin of ~500 fs. To highlight the distinctive insights that can be gained by resolving complex subpicosecond dynamics in a single experiment, we present UV-visible transient emission spectra of technologically relevant wide bandgap zinc oxide. With an enhanced broadband detection, subpicosecond effects such as thermalization, bandgap renormalization, and carrier trapping can be easily assessed, with ramifications for optoelectronics and energy-related technologies.

Instantaneous three-dimensional imaging using supercontinuum and ultrafast optical Kerr gate of tellurite glass

An instantaneous three-dimensional imaging technique using a chirped supercontinuum and an ultrafast optical Kerr gate, in which a sapphire plate and a TeO2-ZnO-Na2O oxide glass were used to generate the chirped supercontinuum and the ultrafast optical Kerr gate, respectively, is demonstrated. This technique is applicable to ultrafast shape measurement, such as shape imaging of moving objects, or imaging of laser-induced refractive index changes in transparent media.