Diechi Sun

Observation of switching phenomena in a nonether polyphenylquinoxaline planar waveguide with two-wavelength nonlinear prism coupling

We present research on nonether polyphenylquinoxaline film waveguides, and a scheme for an all-optical switching operation of waveguides is suggested. We use the m-line spectroscopy technique to characterize the guiding modes in the waveguide, and the switching phenomenon is observed with two-wavelength nonlinear prism coupling. The measured response time of the switching signal is less than 10(-9) s.

Third-order nonlinear optical property of a polyphenylene oligomer: poly(2,5-dialkozyphenylene)

Abstract The third-order nonlinear optical (NLO) property of a soluble, π-backbone conjugated polymer poly(2,5-dialkozyphenylene) (for abbreviation called dialkozy-PP) is studied at the picosecond time region. The near resonance third-order hyperpolarizability γ xxxx at 532 nm is 8.2×10 −30 esu, and the corresponding macroscopic third-order susceptibility χ (3) (− ω , ω , ω , − ω ) and nonlinear refractive index n 2 are estimated to be 6.3×10 −10 esu and 1.4×10 −8 esu, respectively. The half-width of the laser pulse is 35 ps.

Third-order nonlinear optical property of a heterocyclic ladder polymer

Abstract The third-order nonlinear optical (NLO) property of a processable, low-absorption and high thermal stable material, non-either PPQ, is studied. The near-resonance third-order hyperpolarizability γ xxxx is measured to be 8.2×10 −30 esu at 532 nm, its response time is faster than 35 ps (the measurement is limited by the pulse width of the laser used). The corresponding third-order NLO susceptibility χ (3) (− ω , ω , ω , − ω ) is estimated to be 3.6×10 −10 esu and the figure of merit χ (3) α =9×10 −12 esu is larger than that of most currently known nonlinear optical polymers.

Excited-state enhancement of the third-order nonlinear optical susceptibility of nonether polyphenylquinoxaline

The microscopic third-order nonlinear-optical susceptibility gamma(-omega; omega, omega, -omega) of a conjugated polymer, nonether polyphenylquinoxaline, was observed to be enhanced by two times from 355-nm optically pumped excited-state populations under the condition of unsaturated pumping. We studied the time evolution of the enhancement and verified by a fluorescence measurement that the excited-state enhancement of gamma(-omega; omega, omega, -omega) is proportional to the population of the excited state.

The observation of lasing wavelength shift from the reflection center of an Ytterbium doped fiber grating laser

In an Ytterbium doped fiber laser, lasing wavelength red shift from the reflection center of fiber Bragg grating has been observed. The wavelength shift is about half of the grating bandwidth and it does not depend on the temperature or the reflection of fiber Bragg grating. Some gain mechanism or re-absorption may be the reason for this observation.

Particle behaviour of femtosecond optical pulses

Abstract When femtosecond optical pulses propagate through the boundary of the vacuum and an electro-optic material, a transition radiation would be emitted, as well as Cerenkov radiation produced by the material. It has been found theoretically that the electric field of both kinds of radiation is an extremely fast transient and the peak of the radiation is in the far infrared.

Influence of colliding pulses on the chirp production of a saturable absorber

Abstract The influence of colliding pulses on the frequency shift and the chirp produced by the self-phase modulation of an absorbing dye and the nonlinear refractive index of the solvent has been investigated. The chirp arising from the anomalous dispersion of DODCI and its photoisomer has also been calculated.

Study on self-frequency-shift of femtosecond pulse in nonlinear dispersion medium using time-resolved cross-phase modulation method

A time-resolved cross-phase modulation method combined with a modified nonlinear Schrodinger equation is used to study the effects of nonlinear response time on the propagation of ultrashort pulses in nonlinear dispersion media. Evolution of cross-phase modulation spectrum with the different time delay between the probe pulse and pump pulse is simulated using split-step Fourier method. It is shown that both normal self-frequency-shift-red-shift and abnormal self-frequency-shift-blue-shift can occur in the frequency domain for the probe pulse, and a satisfactory theoretical interpretation is given.

Intensive two-photon absorption in nonether polyphenylquinoxaline (PPQ) conjugated polymeric film

Two photon absorption (TPA) with the TPA coefficient (beta) equals 0.59 cm/MW was obtained for polyphenylquinoxaline film by using Z-scan technique at 532 nm wavelength of a passively mode-locked Nd:YAG laser. This was, to our knowledge, the largest ultrafast TPA in conjugated polymers ever reported. And it was shown that the corresponding imaginary part of the third order optical susceptibility (chi) (3) shared an equivalent importance with the real part. The resultant value of (chi) (3), 2.4 X 10-10 esu, was in a good agreement with the reported value.

Theoretical Study of Direct Measurement of Nonlinear Response Time of Conjugated Polymer Based on Cross-Phase-Modulation

In this paper, we present a time-resolved pump-probe method based on cross- phase-modulation (XPM) to measure nonlinear response time. The nonlinear response time can be determined by comparing the self-frequency-shift curve obtained from the numerical calculation with the experimental results.