Kikuo Ujihara

Reflectivity of Metals at High Temperatures

The reflectivity and other optical constants of metals at high temperatures are discussed on the basis of the Drude theory and the theory of electron‐phonon collision. The electron‐phonon collision frequency is dependent on the temperature through the temperature dependence of the phonon population. The temperature dependence of the collision frequency determines that of optical properties of metals. Variations of the real and the imaginary parts of the dielectric constant and of the complex refractive index with temperature are considered. General expressions for the temperature coefficients of the optical constants are given. The reflectivity is shown to decrease with increasing temperature. Numerical calculations were carried out for several metals at a few wavelengths and at temperatures from room temperature to their melting temperatures. The results are given in graphs and in a table. Curves for the reflectivity show that the absolute value of the temperature coefficient of the reflectivity is greater for a metal having a lower reflectivity at room temperature. Calculated values of the reflectivity at room temperature are in reasonable agreement with handbook data. However, the calculated reflectivity for silver at its melting point is not coincident with the reported experimental data (the only data available at present), in spite of the qualitative agreement between our results and the experiment. A brief discussion on possible explanations of the discrepancy is made.

Spontaneous emission and oscillation in a planar microcavity dye laser

Characteristics of a planar microcavity laser using rhodamine 6G with pulsed excitation is studied. Theoretical aspects of controlled spontaneous emission and oscillation in a planar microcavity laser are discussed. The measured spectrum and the angular divergence of spontaneous emission below threshold are in good agreement with theory. The angular divergence yields the radius of the cavity quasimode. The spontaneous emission coupling ratio obtained from the measured input‐output characteristics is in reasonable agreement with the theoretical value. The expression for the coupling ratio derived for a Fabry–Perot‐type microcavity is shown to be essentially equal to that of a closed cavity or guided mode cavity derived by Yamamoto, Machida, and Bjork [Phys. Rev. A 44, 657 (1991)]. The observed spectral behavior near the threshold approximately follows the Schawlow–Townes formula, but for a limited range of output power. The observed spectrum and divergence above threshold indicate incoherence much worse th...

Spontaneous Emission in a Very Short Optical Cavity with Plane-Parallel Dielectric Mirrors

A detailed account of the calculation on the spontaneous emission rate in a very short optical cavity with plane-parallel dielectric mirrors is given. A cavity model consisting of a pair of plane dielectric slabs is used. Guided modes as well as outgoing modes are considered. The emission rate from a two-level atom is calculated under quantum-mechanical perturbation approximation. The enhancement factor for the rate is found to be of the order of unity except for extremely short cavities. The concept of quasimodes in a very short cavity and their effective area are discussed in relation to the enhancement factor. The coupling ratios into various quasimodes are derived.

INTENSITY FLUCTUATION OF A PULSED PLANAR MICROCAVITY LASER

Probability distributions of the peak output power from planar microcavity dye lasers with pulsed excitation have been studied experimentally. Two microcavities were used, one operating possibly with a single mode and the other possibly with a number of modes. These expectations are based on the relative magnitude of the mode radius and the pump beam radius. In the former cavity an exponential‐like distribution was observed below threshold, which indicates single‐mode operation. In the latter cavity a single‐peaked distribution appeared even below threshold indicating multiple‐mode operation. These results are, respectively, in qualitative agreement with theoretical distributions for steady state. That the observed pulse width is large enough to apply steady state distribution equation is shown by calculating the characteristic transient time for the intensity distribution.

Spontaneous emission by two atoms in a planar microcavity

Abstract Spontaneous emission by two atoms in a planar microcavity with partial transmission is analyzed under the dipole approximation and the rotating wave approximation. The strength of mutual interaction between the two atoms during the emission process is calculated as a function of the separation of the two atoms. Under a perturbation approximation, the strength is shown to be factorized into the initial expected correlation of the two dipoles and another factor that depends on the atom–cavity configuration. The latter factor describing the degree of mutual interaction between the two atoms is numerically shown to decrease substantially as the separation of the atoms exceeds the effective mode radius of the planar cavity.

Analysis of spontaneous emission from a planar microcavity—dependence on the refractive index of the cavity region and atomic location

Abstract Spontaneous emission in a model planar microcavity filled with a dielectric medium is analysed quantum mechanically under perturbation approximation assuming an idealized two-level atom. The dependence of the emission rate and the directivity on the atomic location within the cavity is examined numerically on the basis of the perturbation result. The numerically obtained directivity of the spontaneous emission by randomly located atoms is compared with that obtained by algebraically averaging the emission formula over the atomic location.

Spontaneous emission in a micro optical cavity from spectrally broadened atoms

Abstract Spontaneous emission in a micro optical cavity is studied for spectrally broadened atoms. Effects of homogeneous broadening, inhomogeneous broadening and energy-level continuum are nalyzed by the master equation approach. Under the Markov approximation the expressions for the emission rate and the emission line profile are obtained. Numerical examples are given.

Optical and Electrical Characterization of BSO Crystals

Optical and electrical properties of undoped BSO crystals were simultaneously measured and compared. Material parameters determined from optical measurements such as steady-state diffraction efficiency versus light-induced grating spacing and recording time versus light-induced grating spacing characteristics agree well with those determined from electrical measurements, including steady-state photocurrent under a uniform illumination and interference fringe illumination, and transient photocurrent after application of a short light pulse, when a simple band transport model is used for the analyses. The result indicates that the simple electrical measurements are useful for rapid assessment of the crystal as well as for predicting the photorefractive properties.

A Simple Relationship between Directivity and Linewidth of a Planar Microcavity Laser

On the basis of the analysis of the cavity quasimode structure, the relationship between the directivity and the linewidth of the output beam from a laser with a planar microcavity is examined assuming a narrow spectral width of the laser medium. A simple relation is obtained which implies that, in a planar laser, the directivity is determined by the net loss of the laser similarly to the laser linewidth.

Transient response of a photorefractive grating produced in a BSO crystal by a short light pulse

Abstract The transient photorefractive properties of a BSO crystal after illumination by two coherent light pulses were studied by monitoring the diffracted beam intensity of a HeNe laser beam. The previously observed peculiar response curve, having a dip between the first fast rise and second slower rise, can be explained by a newly developed “four-level” model with two shallow acceptor levels, an inactive ionized acceptor level, and a donor level. The temperature dependences of transient photorefractive properties and transient photocurrent, which were measured for the first time, also support the present model.