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Nonlinear optical phase shift in quantum dots measured by a unique two-color pump∕probe ellipsometric polarization analysis
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View: Figures


Image of FIG. 1.
FIG. 1.

Absorptions (black lines) and corresponding refractive indices (gray lines) of assembled with inhomogeneous broadening, in the cases with (broken lines) and without (solid line) pump pulse. Homogeneous broadening (dotted-dash line) is also shown. A probe pulse with some detuning sees the changes, and , induced by the pump pulse.

Image of FIG. 2.
FIG. 2.

Principle of measurement, where a -polarized pump pulse and a 45° polarized probe pulse are colinearly introduced into the waveguide sample. The figure shows the polarization of the pump and probe pulses through the sample, perpendicular to the propagating direction. The -polarized pump pulse (bold arrow) changes the probe polarization from linear (dotted line) to elliptical (solid line). The phase shift difference and the field change and (not shown here) can be obtained by rotating-polarizer detection followed by Fourier transformation analysis.

Image of FIG. 3.
FIG. 3.

Photoluminescence spectrum of the sample measured at room temperature under laser excitation. Two arrows indicate the pump∕probe setup used to obtain the measurements in this paper. It is known that a FWHM of is narrow enough to excite only the ground-state transition with a peak wavelength of 1290 nm. The inset shows the AFM image of formed on the top surface of the sample as a reference. The sheet density was .

Image of FIG. 4.
FIG. 4.

(a) Transmittance of the long waveguide as a function of the input pulse energy densities of -polarized and -polarized pump pulses. The fitting calculation is also shown by the solid lines. (b) Transmittance change, , of -polarized and -polarized probe pulses as a function of the input energy density of the -polarized pump pulse for a long waveguide. Transmittance of the pump pulse itself is also shown. The same curves in log scale are shown in the inset. The wavelengths of the pump and probe pulses and the time delay were , , and , respectively. The large birefringence enables the phase shift measurement by a analysis.

Image of FIG. 5.
FIG. 5.

Decay characteristic in a pump∕probe measurement of the long waveguide. A -polarized pump pulse with a pulse energy density of and a -polarized probe pulse were used.

Image of FIG. 6.
FIG. 6.

(a) Result of a measurement of a long waveguide sample, where the radius and polar angle indicate the detected probe power and the rotation angle of the polarizer, respectively, for various input pulse energy densities. The wavelength of the pump and probe light and the time-delay were set to 1285, 1300, and , respectively. The markers indicate the experimental values and the solid lines indicate calculations using , , and , which are extracted from the experimental values. (b) The derived , and , as a function of input pulse energy density. The obtained from the -polarized-probe transmittance in Fig. 4(b) is also shown. The similarity between the and behavior suggests that is attributed to the absorption saturation for -polarized light.

Image of FIG. 7.
FIG. 7.

transmittance as a function of input pump pulse energy density. -polarized pump∕probe measurement (open circles) and the transmittance in the presence of a pump pulse (dashed line), previously shown in Fig. 4(b), are replotted. The solid line is the calculated probe-transmittance change, derived from the pump-transmittance under the experimental conditions. A homogeneous linewidth of is obtained as a fitting parameter.

Image of FIG. 8.
FIG. 8.

phase shift as a function of the input pump pulse energy density. The large closed circles indicate the experimental values shown in Fig. 6(b). The small circles indicate the results derived from Eq. (1) in various cases: homogeneous linewidth , 10, and with inhomogeneous broadening , and homogeneous linewidth with .

Image of FIG. 9.
FIG. 9.

Consumed power ratio of the pump pulse in long waveguide as a function of the input pump pulse energy density. absorption , two-photon absorption , and transmission through the waveguide are considered as the consumption process. Excited sheet densities along the , , and long waveguides are also shown in the right axis, which are proportional to the phase shift.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Nonlinear optical phase shift in InAs quantum dots measured by a unique two-color pump∕probe ellipsometric polarization analysis