Masao Kitano

Negative group delay and superluminal propagation: an electronic circuit approach

We present a simple electronic circuit which provides negative group delays for band-limited baseband pulses. It is shown that large time advancement comparable to the pulsewidth can be achieved with appropriate cascading of negative-delay circuits but eventually the out-of-band gain limits the number of cascading. The relations to superluminality and causality are also discussed.

Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D 2 line

Experimental results are shown on the frequency stabilization of a GaAlAs laser using a Doppler-free spectrum in the saturated absorption of the Cs-D 2 line at 852.1 nm. The frequency stability (Allan variance) between 3.0 \times 10^{-12} and 1.0 \times 10^{11} was obtained at the averaging time between 0.1 and 1000 s.

Demonstration of negative group delays in a simple electronic circuit

We present a simple electronic circuit that produces negative delays. When a pulse is sent to the circuit as input, the output is a pulse with a similar wave form that is shifted forward in time. The advance time or negative delay can be increased to the order of seconds so that we can observe the advance with the naked eye by observing two light emitting diodes that are connected to the input and the output. The negative group delay in the electronic circuit shares the same mechanism with superluminal light propagation, where the group velocity exceeds the speed of light or even becomes negative.

Frequency-Locking of a GaAlAs Laser to a Doppler-Free Spectrum of the Cs-D2 Line

Preliminary results are reported on the first frequency-locking of a cw GaAlAs laser, operating at room temperature on a single mode, to a Doppler-free spectrum in the saturated absorption of the Cs-D2 line at 852.1 nm.

Ultrafast optical control of group delay of narrow-band terahertz waves

We experimentally demonstrate control over the group delay of narrow-band (quasi continuous wave) terahertz (THz) pulses with constant amplitude based on optical switching of a metasurface characteristic. The near-field coupling between resonant modes of a complementary split ring resonator pair and a rectangular slit show an electromagnetically induced transparency-like (EIT-like) spectral shape in the reflection spectrum of a metasurface. This coupling induces group delay of a narrow-band THz pulse around the resonant frequency of the EIT-like spectrum. By irradiating the metasurface with an optical excitation pulse, the metasurface becomes mirror-like and thus the incident narrow-band THz pulse is reflected without a delay. Remarkably, if we select the appropriate excitation power, only the group delay of the narrow-band THz pulse can be switched while the amplitude is maintained before and after optical excitation.

OPTICAL DETERMINATION OF ALKALI-METAL VAPOR NUMBER DENSITY USING FARADAY-ROTATION

We present a convenient and reliable method for measuring the number density of the alkali metal vapor. The method is based on the diamagnetic Faraday rotation of the plane of polarization of nearly resonant light by the alkali metal vapor, and it is suitable for optically thick vapor where the conventional integrated absorption technique fails.

Observation of Lorentz-group Berry phases in polarization optics

Abstract It is shown that Berrys phase for the Lorentz group can be observed in polarization optics. It appears as the rotation of the polarization plane of linearly polarized light which is passed through an array of linear polarizers. An experiment has been carried out to demonstrate the effect. The phenomenon is closely related to the phase shift due to a cycle of squeezings of light which is predicted by Chiao and Jordan. Connections with Pancharatnams phase is also discussed.

Storage of electromagnetic waves in a metamaterial that mimics electromagnetically induced transparency

We propose a method for dynamically controlling the properties of a metamaterial that mimics electromagnetically induced transparency (EIT) by introducing varactor diodes to manipulate the structural symmetry of the metamaterial. Dynamic modulation of the EIT property enables the storage and retrieval of electromagnetic waves. We confirmed that the electromagnetic waves were stored and released, while maintaining the phase distribution in the propagating direction.

Plane-wave scattering by self-complementary metasurfaces in terms of electromagnetic duality and Babinet's principle

We investigate theoretically electromagnetic plane-wave scattering by self-complementary metasurfaces. By using Babinet’s principle extended to metasurfaces with resistive elements, we show that the frequencyindependent transmission and reflection are realized for normal incidence of a circularly polarized plane wave onto a self-complementary metasurface, even if there is diffraction. Next, we consider two special classes of self-complementary metasurfaces. We show that self-complementary metasurfaces with rotational symmetry can act as coherent perfect absorbers, and those with translational symmetry compatible with their self-complementarity can split the incident power equally, even for oblique incidences.

Frequency-locking of a CW dye laser to the center of the sodium D lines by a Faraday filter

Single-mode CW oscillations at the center of the sodium D lines have been achieved by inserting a Faraday filter in an argon-laser-pumped dye laser cavity. The oscillations at the D 1 and D 2 lines can be selected by choosing adequate values of the sodium temperature and the magnetic field strength. Experimentally obtained conditions to get the single-mode oscillations at the center of the D lines are compared with the theoretically calculated feature of the Faraday filter, and a relatively good agreement has been found. The shifts of oscillation frequencies due to the magnetic field are also discussed.