Femtosecond Optical Kerr Gate Research Articles

Femtosecond optical Kerr effect in normal and grades of cancerous breast tissues as a new optical biopsy method.

This study reports on the first use of the optical Kerr effect (OKE) in breast cancer tissue. This proposed optical biopsy method utilizes a Femtosecond Optical Kerr Gate to detect changes in dielectric relaxation and conductivity created by a cancerous infection. Here, the temporal behavior of the OKE is tracked in normal and cancerous samples of human and mouse breast. These tissues display a double peaked temporal structure and its decay rate changes depending on the tissue's infection status. The decay of the secondary peak, attributed to ultrafast plasma response, indicates that the tissue's conductivity has doubled once infected. A slower molecular contribution to the Kerr effect can also be observed in healthy tissues. These findings suggest two possible biomarkers for the use of OKE in optical biopsy. Both markers arise from alterations in the infected tissue's cellular structure, which changes the rate at which electronic and molecular processes occur.

Femtosecond Optical Kerr Gate in tissues.

The Optical Kerr Effect is investigated for the first time in biological tissues. This nonlinear effect was explored in both human brain and avian breast tissues using a time-resolved femtosecond pump-probe Optical Kerr Gate that looks for phase changes that arise in the probe from the pump induced Kerr refractive index change. The tissue samples produced a unique ultrafast (700-800 fs) doubled peaked temporal signal, which is indicative of interplay between the different ultrafast mechanisms (electronic plasma and molecular) that make up the Kerr index. The unique profile was replicated in theoretical simulations. The properties of the temporal profile varied between samples suggesting that it could be used as a new diagnostic. Understanding this behavior can help improve the scientific understanding of nonlinear spectral diagnostic techniques and potentially create a new Kerr-based optical biopsy method.

High-Transmittance Femtosecond Optical Kerr Gate with Double Gate Pulses Based on Birefringence Effect

An optical Kerr gate (OKG) is an ultrafast optical switch based on the optical Kerr effect. The performance of a conventional OKG depends mainly on Kerr materials. Traditional Kerr materials do not demonstrate both large optical nonlinearity and an ultrafast response time. Therefore, the performance of a conventional OKG is limited by an inherent trade-off between high signal transmittance and fast switching time, which limits its application in many fields. We propose an improved femtosecond OKG with double gate pulses, based on the use of a birefringent crystal to realize an ultrashort switching time, even with a slow-response optical Kerr medium. We assessed the dependence of the double gate pulsed OKG (D-OKG)’s performance on the intensity ratio of the double gate pulses. A transmittance of 50% and a switching time of 142 fs were achieved. The D-OKG is convenient to construct, and its integrated performance is superior to that of a conventional OKG.

Femtosecond optical Kerr gate with double gate pulses: Simulation and experiment

We demonstrated an improved optical Kerr gate with double gate pulses (D-OKG) to realize an ultrashort switching time even with a slow-response optical Kerr medium. A theoretical model of D-OKG was established and the dependence of the D-OKG performance on the relative intensity and the relative delay time of the two gate pulses was investigated. An integrated optimal condition was predicted. The D-OKG was experimentally built and optimized according to the simulation. The dependence of the D-OKG performance on the two gate pulses was confirmed. In our experiment, the achieved values for transmittance and switching time were 45 % and 150 fs, respectively. Compared to the conventional OKG, the D-OKG owns an integrated optimal performance in the femtosecond regime, and has the potential for a wide range of ultrafast optical switch applications.

Femtosecond Optical Kerr Gate With Double Gate Pulses

We proposed an improved femtosecond optical Kerr gate with double gate pulses (DOKG) using a femtosecond laser, in which an ultrashort switching time can be realized even when a relatively slow response optical Kerr medium of carbon disulfide was used. The results showed that when the time delay and the light intensity ratio of the two pump pulses were adjusted to be about 140 fs and 1:0.9, the switching time and the maximum transmission efficiency of the DOKG could be optimized to be about 130 fs and 37%. The DOKG is convenient to be built and offers a good choice for applications based on ultrafast optical switch.

Imaging Transparent Objects in a Turbid Medium Using a Femtosecond Optical Kerr Gate**Supported by the National Natural Science Foundation of China under Grant Nos 61427816 and 61690221, and the Collaborative Innovation Center of Suzhou Nano Science and Technology.

A femtosecond optical Kerr gate time-gated ballistic imaging method is demonstrated to image a transparent object in a turbid medium. The shape features of the object are obtained by time-resolved selection of the ballistic photons with different optical path lengths, the thickness distribution of the object is mapped, and the maximum is less than 3.6%. This time-resolved ballistic imaging has potential applications in studying properties of the liquid core in the near field of the fuel spray.

Depth-resolved ballistic imaging in a low-depth-of-field optical Kerr gated imaging system

We demonstrate depth-resolved imaging in a ballistic imaging system, in which a heterodyned femtosecond optical Kerr gate is introduced to extract useful imaging photons for detecting an object hidden in turbid media and a compound lens is proposed to ensure both the depth-resolved imaging capability and the long working distance. Two objects of about 15-μm widths hidden in a polystyrene-sphere suspension have been successfully imaged with approximately 600-μm depth resolution. Modulation-transfer-function curves with the object in and away from the object plane have also been measured to confirm the depth-resolved imaging capability of the low-depth-of-field (low-DOF) ballistic imaging system. This imaging approach shows potential for application in research of the internal structure of highly scattering fuel spray.

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.

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.

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.

High contrast ballistic imaging using a femtosecond optical Kerr gate of SrTiO3 crystal

We investigated a ballistic imaging technique using a femtosecond optical Kerr gate (OKG) made of SrTiO3 crystal (STO). High-contrast images of a 1.41 line pairs per mm (lp mm−1) section of the resolution test chart placed behind a turbid medium were obtained. The STO OKG had greater capacity to acquire high quality images at a high optical density than the quartz OKG, showing that the STO is a promising OKG medium due to its large nonlinear susceptibility.

Pump power dependence of the spatial gating properties of femtosecond optical Kerr effect measurements

The pump power dependence of the spatial gating properties of femtosecond optical Kerr gate (OKG) was investigated using coaxial two-color optical Kerr measurements in CS2. As the pump power increased, the spatial pattern of the optical Kerr signals changed from a Gaussian spot to a ring form, and then a spot surrounded by a concentric ring, successively. By comparing the experimental data with the calculation results and measuring the pump power dependence of the OKG signal intensity, we demonstrated that the spatial variation of OKG transmittance could be attributed to the non-uniform spatially distributed phase change of the probe beam, due to the transient birefringence effect induced by pump beam with transverse mode of a Gaussian distribution.

Efficient optical Kerr gate of Bi2O3–B2O3–SiO2 glass for acquiring high contrast ballistic imaging in turbid medium

We investigated the ballistic imaging of a 1.41 line pair mm−1 section of a resolution test chart hidden behind a solution of polystyrene spheres with a femtosecond optical Kerr gate (OKG). A better transillumination image contrast could be acquired with an OKG of Bi2O3–B2O3–SiO2 (BI) glass than that with an OKG of fused silica in a highly scattering media, which indicated that the BI glass was a better OKG medium due to its large nonlinear refractive index.

High contrast ballistic imaging using femtosecond optical Kerr gate of tellurite glass

We investigated the ballistic imaging technique using femtosecond optical Kerr gate of a tellurite glass. High contrast images of an object hidden behind turbid media were obtained. Compared to the conventional femtosecond optical Kerr gate using fused quartz, the optical Kerr gate using tellurite glass has more capacity to acquire high quality images of the object hidden behind a high optical density turbid medium. The experimental results indicated that the tellurite glass is a good candidate as the optical Kerr material for the ballistic imaging technique due to its large optical nonlinearity.

Chirp structure measurement of a supercontinuum pulse based on transient lens effect in tellurite glass

We demonstrated the controllable acquisition of optical gated spectra from a chirped supercontinuum (SC) pulse based on ultrafast transient lens (TrL) effect. Comparing with CS2, the gated spectra had much narrower spectral bandwidths using tellurite glass (Te glass) as the nonlinear medium due to its ultrafast nonlinear response. Experimental results showed that the chirp structure of the SC pulse measured by TrL method was quite accordant with that measured by femtosecond optical Kerr gate method.

Study on the Third-order Nonlinear Optical Properties of bis(tetraethylammonium) bis(1,3-dithiole-2-thione-4,5-dithiolato)cadium

A dmit2- salt: bis(tetraethylammonium)bis(1,3-dithiole-2-thione-4,5-dithiolato)cadium (CADMIT) was synthesized. The Optical Kerr Effect (OKE) signal of its acetonitrile solution was measured by femtosecond optical Kerr gate technique. Using CS2 OKE signal as reference signal measured under identical conditions, the third-order optical nonlinear susceptibility, c(3), of the sample solution was obtained to be about 2.98 x 10-14 esu at the concentration of 1.57 x 10-3 M. The second-order hyperpolarizability of its molecular was estimated to be as large as 1.23 x 10-32 esu. Its response time was about 195 fs, which is believed to be the contribution from the delocalized electrons.

Femtosecond nonlinear optical property of a TeO2–ZnO–Na2O glass and its application in time-resolved three-dimensional imaging

Compared with bismuth glasses and chalcogenide glasses, tellurite glasses have a wider transparency window. Especially, these glasses with excellent transparency in visible region could offer a larger dynamic range for the time-resolved simultaneous three-dimensional imaging based on the optical Kerr gate (OKG). We investigated the ultrafast nonlinear optical properties of a TeO2–ZnO–Na2O glass using a femtosecond optical Kerr gate at wavelength of 800nm. The nonlinear refraction n2 and the ultrafast nonlinear response time of the tellurite glass were estimated to be 4.56×10–15cm2/W and less than 200fs, respectively. We also demonstrated the time-resolved simultaneous three-dimensional imaging using the tellurite glass as the Kerr medium, which indicated that tellurite glasses may also be good candidates as the Kerr media for the time-resolved imaging based on the OKG.

Nonlinear optical study of palladium Schiff base complex using femtosecond differential optical Kerr gate and Z-scan techniques

A femtosecond differential optical Kerr gate (DOKG) and Z-scan techniques, have been applied to investigate the third-order optical nonlinearity of composite film of the coordination complex [PdLPPh 3] (L=N-(2-pyridyl)-N′-(salicylidene)hydrazine, PPh 3=triphenylphosphine). Film exhibits superior nonlinear optical properties in the near-infrared spectral region. The nonlinear response time and third-order nonlinear optical susceptibility of complex were found to be≤90 fs and 3.9×10 −10 esu, respectively. The Z-scan result shows that saturable absorption property of the film and its nonlinear absorption coefficient of the sample was found to be −23 cm/GW.

Third-order nonlinear optical properties of C<sub>60</sub>-doped bulk material and its application in ultrafast optical Kerr gate

The ultrafast third-order nonlinear optical properties of C60+ vinyltriethoxysilane H2C=CHSi(OC2H5)3 (C60+VTES) sol-gel were investigated by the femtosecond optical Kerr gate (OKG) technique at 800 nm. The third-order optical susceptibility was measured to be 5.42 × 10−14 esu for C60+VTES at a weight concentration of 0.06 wt.%. Using C60+VTES as the OKG material, we acquired a series of narrow bandwidth and symmetric gated spectra continuously from the chirped white light continuum generated in water with femtosecond laser pulses. The gated spectra obtained using the C60+VTES OKG have distinct superiorities compared with CS2.

Measurements of the scattering coefficients of intralipid solutions by a femtosecond optical Kerr gate

An ultrafast optical Kerr gate (OKG) in femtosecond time scale was used to determine the scattering coefficients of intralipids, in which the BI2O3-B2O3-SiO2 oxide glass was employed as the Kerr medium. Because of the joint action of the time gate and a transient spatial gate that was induced in the Kerr materials by the gating beam, more precise scattering coefficients could be obtained. Our experimental results show that, for low turbid media, the scattering coefficients measured using the OKG method are similar to those measured using the collimated transmittance (CT) approach, while for highly turbid media, the results obtained using the OKG method are bigger than those using the CT approach.