Self-diffraction Effect Research Articles

Ring shaped fs supercontinuum with a thermally induced self-diffraction effect.

A broadband femtosecond supercontinuum (SC) light with a dark core has been generated in a pump-probe type geometry. It has been achieved by introducing a small thermal perturbation in a highly absorbing medium with a continuous wave pump laser. The SC was generated with the help of a photonic crystal fiber and a nJ femtosecond oscillator. Numerical simulations for the system were done by employing the Fresnel-Kirchhoff formula. The power dependence of the dark core diameter was also studied experimentally, and the results agree well with numerical simulations. The dark core size can be controlled by varying the input power of the pump beam.

Holographic formation of photon structures by Bessel-like and Gaussian light fields in photopolymer materials taking into account two-beam interaction and small contrasts

This paper presents a theoretical model of the holographic formation of photon structures (PS) in a photopolymer material (PPM) by Bessel-like and Gaussian light beams, taking into account the self-diffraction of recording light beams in areas of low contrast of the interference pattern. It was demonstrated by numerical simulation and experiment that the influence of the self-diffraction effect leads to an increase in the level of the side maxima of the diffracted light beam.

Enhanced nonlinear optical properties of solution dispersed carbon dots decorated graphene oxide with varying viscosity

Nonlinear optical response of solution dispersed Carbon Dots decorated Graphene Oxide (CDs-GO) with viscosity has been investigated. Spatial self-phase modulation and Z-scan technique were utilized to study the nonlinearity of the composite which was synthesized by microwave assisted route. The strong self-diffraction effect was observed on excitation with 403,450 and 532 nm wavelengths from a DPSS laser. The estimated value of χ(3) is 3.2 × 10−4 esu in water obtained using SSPM technique. The nonlinearity of the sample is due to the reorientation of the graphene oxide sheet with the strong electromagnetic field of lasers and two photon absorption. Enhanced nonlinearity observed with increase in input pump power and viscosity of the solvents endows them new potentials in nonlinear optical applications.

Influence of Self-Diffraction Effect on Femtosecond Time-Resolved Single-Shot Optical Kerr Measurements**Supported by the National Natural Science Foundation of China under Grant Nos 11304242, 11474078 and 61427816, the Natural Science Basic Research Plan in Shaanxi Province under Grant No 2014JQ1024, the Financial Support from China Postdoctoral Science Foundation under Grant Nos 2013M542335 and 2014T70924, and the Collaborative Innovation Center of Suzhou

Femtosecond time-resolved single-shot optical Kerr gating (OKG) measurements are performed by focusing the probe pulse and using a cylindrical lens to introduce a spatially encoded time delay with respect to the pump pulse. By measuring the pump power and polarization dependence of the OKG signals in CS2, the contribution of self-diffraction effect which is independent of the nonlinear response time of the material is directly observed on the rising edge of the time-resolved OKG signals. The influence of the self-diffraction effect on the optical Kerr signal could be controlled effectively by varying the polarization angle between pump and probe pulses.

弱磁场中向列相液晶TEB30A薄膜自衍射现象研究

弱磁场中向列相液晶TEB30A薄膜自衍射现象研究

Self-diffraction and high nonlinear optical properties of carbon nanotubes under CW and pulsed laser illumination

In this work, self-diffraction effect in carbon nanotubes (CNTs) that were dispersed on N,N-dimethylformamide (DMF) solvent is studied. Third-order nonlinear optical coefficients of this nano-suspension are measured using z-scan technique and high nonlinearity is observed. Nonlinear refraction index of the order −10−6cm2W is obtained due to the thermal effect and the nonlinear interaction of the light and the surface plasmonic electrons. Optical diffraction rings of the sample under He–Ne laser illumination at a wavelength of 632.8nm were observed and intensity distribution of the rings is explored. At last, optical limiting performance of CNTs is investigated under irradiation by a continuous wave (CW) He–Ne laser. The optical limiting behavior is investigated by using transmission measurement through the sample and our studies indicate that this material is a potential candidate for optical limiting applications in low power CW regime.

Reduction of the angular dispersion in self-diffraction signals by using a prism

Self-diffraction effect has very important applications in the field of femtosecond laser, such as to improve the temporal contrast of femtosecond pulses, to be used as the reference pulse of self-reference spectral interferometry, and as the signal of self-diffraction frequency-resolved optical gating, etc. However, in the self-diffraction signal of femtosecond pulses with a broadband spectrum angular dispersion exists obviously, which will limit the application of self-diffraction effect. In this paper, the self-diffraction signal angular dispersion of femtosecond pulses is obviously reduced, when a right-angle prism is located in the light path of an incident beam with an incident angle of 23° to the prism. The experimental result provides a useful reference for the application of the self-diffraction effect to the research of femtosecond laser pulse in the future.

Vectorial self-diffraction effect in optically Kerr medium

We investigate the far-field vectorial self-diffraction behavior of a cylindrical vector field passing though an optically thin Kerr medium. Theoretically, we obtain the analytical expression of the focal field of the cylindrical vector field with arbitrary integer topological charge based on the Fourier transform under the weak-focusing condition. Considering the additional nonlinear phase shift photoinduced by a self-focusing medium, we simulate the far-field vectorial self-diffraction patterns of the cylindrical vector field using the Huygens-Fresnel diffraction integral method. Experimentally, we observe the vectorial self-diffraction rings of the femtosecond-pulsed radially polarized field and high-order cylindrical vector field in carbon disulfide, which is in good agreement with the theoretical simulations. Our results benefit the understanding of the related spatial self-phase modulation effects of the vector light fields, such as spatial solitons, self-trapping, and self-guided propagation.

Self-referenced spectral interferometry based on self-diffraction effect

A new technique of “self-referenced spectral interferometry” is demonstrated based on a self-diffraction effect and applied to the measurement of femtosecond pulses. The reference pulse is the first-order self-diffraction pulse that is generated in a thin bulk medium by the self-diffraction process from the incident pulses. A proof-of-principle experiment succeeded in characterizing a ∼55 fs pulse at 800 nm and a sub-10 fs pulse at 400 nm. The system can be simultaneously used to measure ultrashort pulses by the self-diffraction based on frequency-resolved optical gating.

Ultrafast nonlinear optical response of photoconductive ZnO films with fluorine nanoparticles

The absorptive and refractive third order nonlinear optical properties exhibited by a ZnO thin solid film with fluorine nanoparticles were studied with picosecond and femtosecond pulses using different techniques. We were able to evaluate the photoconductivity of the material and the quenching of the induced birefringence observed in the presence of two-photon absorption. The samples were prepared by a chemical spray deposition technique. In order to investigate the different contributions of the third order nonlinearities of the film, we analyzed the vectorial self-diffraction effect and the optical Kerr transmittance observed in the sample. A dominantly absorptive nonlinearity was measured at a 532 nm wavelength with 50 ps pulses, while nonlinear refraction was found to be negligible in this regime. On the other side, a pure electronic refractive third order nonlinearity without the contribution of nonlinear absorption was detected at 830 nm with 80 fs pulse duration. A quasi-instantaneous optical response and a strong enhancement in the ultrafast nonlinear refraction with the inhibition of the picosecond two-photon absorption mechanism were measured for the case of the femtosecond excitation.

Pump power dependence of Kerr signals in femtosecond cross pump-probe optical Kerr measurements

We investigated the influence of self-diffraction effect on femtosecond cross pump-probe optical Kerr shutter (OKS) measurements for fast response and slow response materials, respectively. In the slow response material of CS(2), a fast response resulted from self-diffraction effect was observed in the time-resolved OKS signals, and the signal intensity showed different pump power dependences at different delay time. For the fast response material of bismuth oxide (BI) glass, the pump power dependence of OKS signals varied when the polarization angle was varied. The pump power dependences of OKS signals for the both materials showed that, the OKS signals resulted mainly from laser induced birefringence effect at low pump powers, and the contribution of self-diffraction effect to OKS signals was enhanced with increasing the pump power.

Stimulated Emission and Optical Third-Order Nonlinearity in Li-Doped ZnO Nanorods

We report the structure and optical properties of semiconductor Li-doped ZnO nanorods. The sample was synthesized by an ethylenediamine-assisted low-temperature hydrothermal technique. The obtained morphology was studied by using high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction techniques. Our sample exhibits a crystalline Wurtzite phase of ZnO grown along the [101] direction. However, the lattice fringes corresponding to a ZnO sample intercalated with Li ions in the growing direction correspond to 2.58 Å instead of 2.46 Å, which is the reflection [101] for the ZnO hexagonal wurzite phase. The morphology of the rods changes dramatically. In the case of ZnO rods intercalated, we obtained a sharp pencil morphology. Large values of two photon absorption were measured as well as an important photoemission response. Near resonance, the stimulated emission of the sample was measured with picosecond pulses at 355 nm, finding a lasing threshold of around 30 MW/cm2 (780 μJ/cm2). At this wavelength, the value of β = 2.4 × 10−4 m/W was measured. Far from resonance, by measuring a self-diffraction effect at 532 nm, we obtained a value of β = 1 × 10−10 m/W and an important pure electronic nonlinear refraction value n2 = −1 × 10−15 m2/W.

C60掺杂向列相液晶薄膜的激光诱导自衍射现象研究

C60掺杂向列相液晶薄膜的激光诱导自衍射现象研究

Influence of self-diffraction effect on femtosecond pump-probe optical Kerr measurements

We investigated influence of the self-diffraction effect on optical Kerr signals of Bi2O3-B2O3-SiO2 glass (BI glass) and CS2 in femtosecond non-collinear pump-probe optical Kerr experiments. By measuring the dependence of the Kerr signals on the pump power and on the polarization angle between pump and probe beams, we found that the optical Kerr signals of CS2 consisted of two components: a fast response and a slow response,which were attributed to the self-diffraction effect and the photoinduced birefringence effect, respectively. The contribution of the self-diffraction effect to the Kerr signals increased with increase of the pump power. For the BI glass, no evident influence of self-diffraction on the Kerr signals was observed.

Self-diffracting effects in hybrid materials

The authors experimentally demonstrate self-diffraction effect in a hybrid material. Patterns at different light intensity levels were obtained. A dependence of the number of diffraction rings with the intensity of laser is observed.

Comment on: Novel method for ultrashort laser pulse-width measurement based on the selfdiffraction effect

A new technique for the measurement of the pulse-width of ultrashort optical pulses has been recently proposed [1]. I argue in this comment that such a technique is unable to get any temporal information on an ultrashort pulse, based on the absence of a time-non-stationary element in the proposed setup.

Novel method for ultrashort laser pulse-width measurement based on the self-diffraction effect

Previous pulse-width measurement methods for ultrashort laser pulses have broadly employed nonlinear effects; thus any of these previous methods may experience problems relating to nonlinear effects. Here we present a new pulse-width measuring method based on the linear selfdiffraction effect. Because the Talbot effect of a grating with ultrashort laser pulse illumination is different from that with continuous laser illumination, we are able to use this difference to obtain information about the pulse width. Three new techniques - the intensity integral technique, the intensity comparing ratio technique, and the two-dimensional structure technique - are introduced to make this method applicable. The method benefits from the simple structure of the Talbot effect and offers the possibility to extend the measurement of infrared and x-ray waves, for which currently used nonlinear methods do not work.

Observation of self-diffraction effect in Acid blue 7 dye soaked gelatin films

Abstract Permanent self-diffraction gratings are formed in red sensitive Acid blue 7 dye soaked gelatin films under illumination of an interference pattern by two linearly polarized beams from a He-Ne laser at 632.8 nm. Growth of the self-diffraction grating is monitored by measuring intensities of various diffraction orders. Systematic studies are carried out to investigate the influence of various parameters involved in diffraction efficiency of the grating such as time of exposure, concentration of dye in the gelatin-coated plate, intensity of interfering beams and intensity ratio of interfering beams. Efficient gratings with ten diffracted orders are formed. Several interesting observations are made by blocking one of the writing beams and an attempt is made to analyse these results.

Observation of self-diffraction effect in acid blue 7 dye soaked gelatin films

Permanent self-diffraction gratings are formed in red sensitive Acid blue 7 dye soaked gelatin films under illumination of an interference pattern by two linearly polarized beams from a He-Ne laser at 632.8 nm. Growth of the self-diffraction grating is monitored by measuring intensities of various diffraction orders. Systematic studies are carried out to investigate the influence of various parameters involved in diffraction efficiency of the grating such as time of exposure, concentration of dye in the gelatin-coated plate, intensity of interfering beams and intensity ratio of interfering beams. Efficient gratings with ten diffracted orders are formed. Several interesting observations are made by blocking one of the writing beams and an attempt is made to analyse these results.

Approximate analytic solution of photochromic and photorefractive gratings in photorefractive materials

We have developed an approximate analytic expression of two wave mixing for absorption and phase gratings in photorefractive materials taking into account self-diffraction effect of two writing beams. We also present experimental evidence of simultaneous recording of the mixed gratings recorded in BaTiO 3 crystal and measure grating amplitudes and phases relative to intensity grating by using grating translation technique, showing good agreement with the theory developed.