Time-resolved Pump-probe Method Research Articles

Wavelength-dependent optical nonlinear response of vanadium diselenide

The wavelength-dependent and ultrafast nonlinear optical response of vanadium diselenide (VSe2) in the visible to near-infrared spectrum are experimentally investigated, which shows broadband saturation absorption and self-focusing characteristics, and obtained the maximum nonlinear absorption coefficient and nonlinear absorption coefficient are −4.058 × 10−10 m/W and 6.043 × 10−17 m2/W, respectively. Meanwhile, the ultrafast carriers dynamic response of VSe2 is studied by using time-resolved pump-probe method, and the ultrafast response time of 0.65 ps is obtained. Our results show that VSe2 is an excellent nonlinear optical material and has great application potential in the field of nonlinear optics.

Measurement of non-linear optical coefficients of chalcogenide glasses near the fundamental absorption band edge

A time-resolved pump-probe method is used for the evaluation of non-linear optical coefficients of chalcogenide glasses from the As-S-Se and Ge-Se systems near their fundamental absorption band edges. The results are analyzed via comparison with the spectral dependencies of the non-linear optical coefficients of crystalline semiconductors; the role of electron transitions through the gap states of chalcogenide glasses is discussed.

Identification of the cationic excited state of cyclopentanone via time-resolved Ion yield measurements

We report the experimental evidence of the one-photon resonance in the cationic excited state of cyclopentanone using the femtosecond time-resolved pump-probe method. The transients of the parent ion and the C2H4+ fragment exhibit constant depletion in the pump-probe delay time up to 7ps, however, that of the C4H8+/C3H4O+ fragment presents formation behavior. By recording dependence of the ion yields as the probe laser intensity, we demonstrate one 400-nm photon resonance in the cationic excited state, which is assigned as the D4(2A) cationic state based on the theoretical calculations. Possible dissociation mechanism of the D4 state is also discussed.

Ultrafast Photodissociation Dynamics of the F State of Sulfur Dioxide by Femtosecond Time-Resolved Pump-Probe Method

A femtosecond pump-probe method is employed to study the dissociation dynamics of sulfur dioxide. SO2 molecules are excited to the F state by absorbing two photons of 267 nm femtosecond laser pulses, and ionized by 400 nm laser pulses at different delay times between the two lasers. Transients of both parent ions (SO+2) and the fragment ions (SO+, S+ and O+) are observed. The SO+2 transient can be well fitted to a biexponential decay comprising a fast and a slow component of 280 fs and 2.97 ps lifetimes, respectively. The SO+ transient consists of two growth components of 270 fs and 2.50 ps. The results clearly show that the F state of SO2 dissociates along an S-O bond. The transients of S+ and O+, however, have different behavior, which consist of a fast growth and a long decay component. A possible mechanism of the fragment formation is discussed to understand the dissociation dynamics of the F state of SO2.

Critical behavior of a photodisordered spin system in doped manganite

Dynamics of the spin system has been investigated in a ferromagnetic ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ film by means of a time-resolved pump-probe method. In a weak excitation condition, the relaxation time $\ensuremath{\tau}$ increases critically on approaching the critical temperature ${T}_{\mathrm{C}}(=262$ K) from the low-temperature side as $\ensuremath{\tau}\ensuremath{\propto}|{T/T}_{\mathrm{C}}\ensuremath{-}1{|}^{\ensuremath{-}1.39}$ for $T\ensuremath{\gtrsim}200$ K. Surprisingly, the same scaling relation holds even after strong excitation in a much wider temperature range down to $\ensuremath{\sim}10$ K. We will discuss these behaviors in terms of photoinduced growth of the charge-ordering fluctuations.

Ion-beam milling of YBCO thin films and their characterization by time-resolved pump-probe method

YBCO films are exposed to Ar ion beams in order to obtain flat surfaces and they are characterized by the time-resolved reflection pump-probe method excited with femtosecond optical pulses. The amplitudes of the reflectivity change of the ion-beam processed films are smaller than that of the as-grown ones and the decay time decreases by the ion-beam etching. These results are discussed in relation to the changes of the supercarrier density and the relaxation time of quasiparticles by the ion-beam milling.

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.

Ultrafast 1.55-μm photoresponses in low-temperature-grown InGaAs/InAlAs quantum wells

Doping with Be was found to be very effective for shortening of carrier lifetime in InGaAs/InAlAs multiple quantum wells (MQWs) grown at low temperature by molecular beam epitaxy. The MQW materials have carrier lifetimes controllable from a few tens of picoseconds to 1 ps in the 1.55-μm wavelength region, coupled with a large optical nonlinearity due to an excitonic feature, implying applicability to ultrafast optical devices in the fiber-optic communication. The carrier lifetime was measured by a time-resolved pump-probe method using an optical source based on a 1.535-μm semiconductor laser. We also investigated the resistivity, carrier density, and Hall mobility in the MQWs.