Vol. 27, No. 4 (1978)
1978-02-20
CONTENT
1978, 27 (4): 361-374.
doi: 10.7498/aps.27.361
Abstract +
The laser transition cross sections of YAP:Nd crystals are calculated by using group theory. The values of these cross sections for general elliptically polarized light are shown to be determined by three parameters. The theoretical results are verified by experiments and demonstrated by the construction of a wave length variable laser. We analysed two laser structures in which the transmission matrices are U-matrices, and calculated the polarizations and frequencies of their eigenmodes. Experimental results agree with the theory well. The results obtained in our work can be used in construc-tion of a single longitudinal mode laser with enhance output and to suggest a new method of modulation for lasers.
1978, 27 (4): 375-382.
doi: 10.7498/aps.27.375
Abstract +
In this article we consider the statistical properties of the superposition of a partially polarized speckle pattern and a coherent background in an arbitrary polariza-tion state.
1978, 27 (4): 383-395.
doi: 10.7498/aps.27.383
Abstract +
A pulse "flow-stretching" technique is suggested in an attempt to increase pulse width in the CO2 lasers. The conditions, characteristics and requirements of pulse flow-stretching are elucidated. Optical cavity is located on the downstream of the dis-charge region, or they may be partly overlapped. The pulse width so broadened could be just greater than the time required for the stream to cross over the discharge region. This is an upper limit of pulse stretching. The analytical solution for non-equilibrium relaxation processes without radiation is obtained. The small-signal gain characteristics is presented. By utilizing the theory given in the articles[18,19], we have calculated the power output and the efficiency. The small-signal gain is in the range of nearly a few thousandth to a few hundredth per centimeter and energy efficiency, 5-15%. Influences of gas composition and pressure on the power output and effici-ency have been considered.
1978, 27 (4): 396-412.
doi: 10.7498/aps.27.396
Abstract +
Based on a microscopic molecular model, an analytical expression for the satura-tion intensity is obtained. By taking into account of the changes in gas pressure, temperature and flow velocity, the saturation intensity and small-sgnalgain coefficient at all points in the active region have been calculated under a variety of parameters. We have analysed and discussed the effects of the changes of pressure, flow velocity, gas composition and the discharge specific power on saturation intensity and small-signal gain coefficient. Finally, the calculated values for saturation intensity are compared with experimental results and good agreements are found.
1978, 27 (4): 413-420.
doi: 10.7498/aps.27.413
Abstract +
By selecting appropriate cavity configurations, the astigmatism of optical mode in spherical mirror folded cavities can be partially eliminated and regulated. The codi-tion of anastigmatism elimination for output branch of spherical mirror folded cavities is calculated by means of the transformation circle diagram.
1978, 27 (4): 421-429.
doi: 10.7498/aps.27.421
Abstract +
According to the actual practical condition of acousto-optical deflectors, by solving Dixon equations of abnormal Bragg diffraction under the condition of fixed incident light direction ?1, the functional dependences of the ultrasonic wave direction ?a. which gave rise the acousto-optical interaction and the diffraction light direction ?2 on the frequency f are obtained. From the ?a-f relationship, the important design parameters, i.e., the Bragg bandwidth and the transducer length, can be determined accurately. The ?2-f relationship shows good linearity, hence the previously proposed corrections on scanning linearity appear to be unnecessary.
1978, 27 (4): 430-438.
doi: 10.7498/aps.27.430
Abstract +
The energy levels, selection rules, transition probabilities, spectra and spectral line intensities of an atom with a charged magnetic monopole as its nucleus (known as "monopole hydrogen atom") are calculated. The intensity ratio of three characteristic absorption lines (2774?, 2734?, 2191?) is 37:50:6.
1978, 27 (4): 439-447.
doi: 10.7498/aps.27.439
Abstract +
Starting from the nonlinear differential equation for a non-uniform ferromagnet in mean field approximation, we apply the bifurcation theory to discuss the pheno-mena of magnetic phase transition. It is shown that (1) the Curie point of the system is determined by the maximium eigenvalue of linearized equation; (2) the space varia-tion of magnetization just below the Curie point is described by the corresponding eigenfunction; (3) the temperature dependence of magnetization is represented by the parameter a(T)～(l-T:Tc)1/2. In the later parts of our paper, the application of this method is illustrated by examples of thin films and a simple model proposed for describ-ing non-uniform ferromagnet.
1978, 27 (4): 448-458.
doi: 10.7498/aps.27.448
Abstract +
By using two kinds of wangerin transformations, the external analytical solutions for a set of important conventional configurations with quasi-elliptical cross sections (including such configurations, as elliptical, tear drop, fingerring, etc.) are obtained. These solutions are not subject to the limitation of small aspect ratio. In the vaccum region near the plasma boundary, a simple approximate solution is found.
1978, 27 (4): 459-469.
doi: 10.7498/aps.27.459
Abstract +
In this paper, a theory is presented for the linear acoustic resistance of an orifice in an infinite thin plate. For high frequency and/or great orifice, an approximating formula is derived, while the limiting value is obtained in opposite case. Theoretical calculations are in consistency with experimental data. Finally, an approximating formula which is applicable for the whole frequency range is given.
