Guoqing Tang

Structural characterization and optical properties of nanometer-sized SnO2 capped by stearic acid

Structure and optical properties of nanometer-sized SnO2 capped by a layer of stearic acid are investigated using TEM, XRD, ESR, UV-visible absorption spectrum, photoluminescence spectra, IR absorption spectra and Z-scan techniques. It is found that such capped SnO2 samples display new optical properties, which will enlarge their applications in nonlinear optics. The relationship between structure and optical properties of the SnO2 nanoparticles is also discussed.

Optical nonlinearities of Fe2O3 nanoparticles investigated by Z-scan technique

Abstract The single beam Z-scan technique has been used to measure the third-order nonlinear refractive index, γ, the two-photon absorption coefficient, s, and the variation of refractive index per unit photoexcited carrier density σ r , and the free carrier absorption cross section σ ab for quantum-confined Fe 2 O 3 nanoparticles coated by a layer of organic molecular in toluene and bare particles in hydrosol. For coated Fe 2 O 3 nanoparticles, the ratio γ/s is enhanced by a factor of five compared to the bare sample. Their figures of merit related to linear and two-photon absorption for ultrafast all-optical devices application were determined.

Biphotonic self-diffraction in azo-doped polymer film

A new nonlinear optical phenomenon, biphotonic self-diffraction (BSD), is reported in azo dye doped in polymer matrix. The first-order and the second-order BSD signals are observed in the experiment. It is demonstrated that the dynamic behaviors of the BSD signals are dependent on the cis-trans isomerization of azo molecules by two color lights.

Spectral discrimination between normal and leukemic human sera using delayed luminescence

In this work, photoinduced delayed luminescence (DL) was used to distinguish serum samples of patients with acute lymphoblastic leukemia from those of healthy volunteers. DL decay kinetics of human serum samples was measured using a homebuilt ultraweak luminescence detection system. It was found a significant difference in the weight distribution of the decay rate between normal and leukemic serum samples. A comparison of the DL kinetics parameters including the initial intensity, the peak decay rate, and the peak weight value was used in making discrimination between normal and leukemic human sera. Results in this work contribute to the development of a novel optical method for the early diagnosis of leukemia.

Optical nonlinearities and transient dynamics of 2-(2′-hydroxyphenyl)benzoxazole studied by single-beam and time-resolved two-color Z-scan techniques

Optical nonlinearities (including nonlinear absorption and nonlinear refraction) and the temporal properties of the nonlinear refraction of 2-(2′-hydroxyphenyl)benzoxazole (HBO) based on excited-state intramolecular proton transfer in its two-photon absorption (TPA) range have been investigated, for the first time to our knowledge, by single-beam and time-resolved two-color Z-scan techniques. By establishing the kinetic model of HBO that is due to the TPA, we obtained the TPA coefficient, the molecular hyperpolarizability of the ground state of the enol tautomer of HBO, and the nonlinear refraction, represented by σr, of the excited state of the keto tautomer of HBO. The theoretical results are in good agreement with the experimental ones, which shows that, on the one hand, the excited-state intramolecular proton transfer of HBO can be achieved through the excitation in its TPA range and that, on the other hand, the optical nonlinearities of HBO are closely related to the dynamics of HBO that are involved in the excited-state intramolecular proton transfer.

Red-band holographic storage in azo dye sensitized by noncoherent light

Biphoton holographic storage recorded with 633-nm He-Ne beams has been investigated in Methyl Yellowdoped polystyrene film sensitized by weak noncoherent light from a low-pressure Hg lamp. It is demonstrated that the holography in the sample is erasable without fading. The dynamic behavior of the hologram is dependent on the cis-trans isomerization by noncoherent light and 633-nm beams and photoinduced heat.

The infrared vibration characteristics of SnO2 nanoparticles

The infrared vibration characteristics of SnO2 nanoparticles with different sizes were studied using the infrared spectra. The Frohlich modes were observed in experiments and compared with the theoretical values. The influence of phonon localization resulting from quantum size effects on the infrared spectra of SnO2 nanoparticles is discussed.

Optical nonlinearities of hypocrellin A with the excitation of nanosecond pulses

Nonlinear absorption and nonlinear refraction in the resonant region and the two-photon absorption (TPA) region of hypocrellin A (HA) have been investigated, for the first time to our knowledge, using the Z-scan technique and intensity-dependent transmittance measurement with nanosecond pulses. At 0.53 μm the effective absorption of the triplet state of the normal form of HA is the dominant mechanism causing the reverse saturable absorption. The refractive nonlinearities of HA can be mainly attributed to the thermal effect. With the excitation at 1.06 μm the optical limiting behavior in HA may be caused by the TPA of its ground state. The ground state of HA exhibits a large real part of second-order hyperpolarizability. By establishing the kinetic model for HA, we obtained several nonlinear optical parameters, such as the cross section of TPA, the absorption cross sections of the excited state and the triplet state of the normal form of HA, and the real part of second-order hyperpolarizability of the ground state of HA. The theoretical results are in good agreement with the experimental ones, which not only shows the completeness of the kinetic model but also demonstrates the close relationship between the optical nonlinearities of HA and its dynamic processes. In addition, HA has been proved to be a potential optical limiting material.

INVESTIGATION ON NONLINEAR TRANSMISSION PROPERTY OF EXCITED STATE PROTON TRANSFER MOLECULE 2-(2′-HYDROXYPHENYL)BENZOXAZOLE

Nonlinear transmission property of excited state proton transfer molecule 2-(2′-hydroxyphenyl)benzoxazole was investigated at 355 nm and 532 nm using picosecond laser pulses. The experiment result shows that the transmissivity of 2-(2′-hydroxyphenyl)benzoxazole is nonlinear at 355 nm but it is linear at 532 nm. The nonlinear transmissivity of 2-(2′-hydroxyphenyl)benzoxazole originates from the larger nonlinearity of tautomer formed in excited state proton transfer process. Therefore 2-(2′-hydroxyphenyl)benzoxazole might be used as ultrafast optical amplitude limit material.

Physical mechanism of delayed luminescence from human serum

The fluorescence spectra, delayed luminescence (DL) spectra and DL decay dynamics of human serum were studied by fluorescence and time resolved emission spectrum technology under different excitation conditions in this paper. The results we obtained are shown as follows: (1) the DL spectrum is similar to the time resolved fluorescence spectrum within 50ns after Ps laser pulse excitation. (2) The intensity and decay time of DL from the serum samples are dependent on excitation power and irradiation time. Under fixed excitation power, the longer irradiation time is, the higher the DL intensity; after the excitation energy reaches about 200mJ, the DL intensity is nearly unchanged. The change of DL decay time follows the similar regulation to that of DL intensity. (3) As the excitation energy increases, the spectral distribution of the relative intensities exhibits an observable change. The higher the excitation energy is, the stronger the relative intensity at short wavelength region. The results show that the delayed luminescence of human serum is mainly originated from its delayed fluorescence, phosphorescence, and induced bio-photon emission. These results may be also useful for the development of serum diagnosis technology.