Experimental Techniques and Elements
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The concept of the free-vortex aerodynamic windows(FADW) is one of the best effective methods taking the place of the conventional beam output crystal windows of high power laser. An experimental model of the supersonic free-vortex aerodynamic window has been designed and made in our latest study. This paper studies the aero-optical phenomena of the FADW′s supersonic jet to study the laser optical quality degradation caused by the free-vortex jet, and to find out the relation of output laser beam quality through the FADW to the structure of the FADW′s supersonic jet. First it studies the beam quality using the methods of far-field beam profile measurement and lateral shearing interferometry, and then it uses the principle of matrix-optics interpreting the large-scale phase distortion in detail. At last the structure of FADW′s jet has been studied by means of shadowgraphy.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.425-431
The changes in wavelength and attenuation of temperature-insensitive long period fiber grating subjected to bends with curvatures from 0 to 4.4 m-1 are examined. The wavelength change with curvature is nonlinear and the minimum detectable curvature change is 0.03 m-1.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.432-439
Holography and Information Processing
A digital holographic method that can be used for the simultaneous measurement of slopes of a deformed object in different directions is described in this paper. In this method, two holograms are recorded numerically under the normal and deformed states of the specimen, and two object waves are numerically calculated from these two holograms. The slopes corresponding to different directions are measured by superposing the two object waves with appropriate shifts. It is a superior method in regard to the simple experiment setup, the flexibility in handing the data, and the high quality phase maps.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.455-459
Rectangular annular pupils are designed. The transverse intensity distribution and the superresolving characteristics of the pupils in the focal plane are analyzed. The influences of total annular zone numbers and the central core magnitude on the light efficiency (the Strehl ratio S), the superresolving power (the normalized spot size G) and the intensity of sidelobe are studied in detail. The properties are different for two kinds of pupils: one with total odd annular zone numbers and another with total even annular zone numbers. Circular annular pupils are also discussed and the comparison between them is given.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.460-464
The most promising 3D display technology lies in holographic display system. Kinform, whose theoretical diffraction efficiency is 100%, is the promising type of hologram. It is found that one of the greatest obstacles to the practical application of kinoform is the computational speed. A new model to increase the computational speed is proposed to solve the problem. In the proposed model named horizontal parallax only (HPO) kinoform, the vertical parallax is omitted because the human visual system cannot perceive the vertical parallax. Therefore, the computational speed for HPO kinform is many times faster than that for full parallax kinform. In this paper, both the theoretical basis and the experimental results of HPO kinoform are discussed.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.465-468
A. B. Vannes
The velocity distribution of powder particles in the laser cladding has an important influence on the motion of liquid in the laser molten pool. In this paper, considering the carrier gas leaving the nozzle to be a steady jet, the velocity distribution of the powder particles is obtained, which can be used as input data in the modelling of the laser cladding.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.469-474
According to the resonator transform circle theory, the focal length of thermal lens of laser media in laser diode end-pumped solid-state lasers is analyzed and measured with a simple method. A 30W 808nm LD pumped YVO4 laser is developed and characterized.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.401-404
By using a passive Q-switch with GaAs saturable absorber, the Q-switched self-frequency doubling NYAB laser at 0.531μm has been successfully realized. The pulse width and the single pulse energy are measured. The numerical solutions of the coupling wave rate equations are in agreement with the experimental results.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.405-408
The output of Nd∶YAG single-pass laser amplifiers is studied analytically and experimentally. Methods of analysis for single-pass Nd∶YAG laser amplifier are presented. A flashlamp-pumped Q-switched Nd∶YAG oscillator/amplifier laser system has been developed with the average output power of 121.5 W.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.409-412
Laser Physics and Laser Chemistry
By means of time-evolution operator, the emission spectrum from two two-level entangled atoms in Bell states interacting with a single-mode cavity field in the Fock state has been studied in the paper. The physical spectrum expression of radiation emitted by the atoms is given out for each Bell state. In general, the spectrum shows the symmetrical multi-peak structure and the symmetrical three-peak structure with the strong optical input. Bell states composed of two identical atoms can be partially distinguished in view of the characterizations of their emission spectrum.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.413-417
The interaction of the light field with two-level atoms possessing dipole-dipole interaction is studied. It is shown that a light field at coherent state can produce a squeezed atom laser.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.418-420
In this paper, the results of an experimental study on 6P3/2+6P3/2→7PJ+6S1/2 energy pooling collisions are presented. The experiment was carried out in cesium vapor using an external cavity diode laser for excitation under different temperatures. It is found that the response of fluorescence intensity to the frequency of excitation laser shows a two-peak phenomenon.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.421-424
Optical Communications and Its Elements
The comb-like filter characteristic of a Fabry-Perot etalon in frequency domain was deployed to filter out the discrete spectral lines of injected 10GHz optical pulse train. By changing the free spectral range and obtaining the spectral components spaced to 4 and 6 times of the repetition rate, the pulse trains with 40 GHz and 60 GHz were successfully obtained.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.435-439
Research on the one-mirror-inclined three-mirror-cavity (OMITMiC) photodetectors in the laboratory is reported. In the structure of photodetectors, it is the inclined-mirror that makes the filtering cavity and the absorption cavity decoupled, thus narrow spectral response linewidth, wavelength-tunable and high quantum efficiency can be achieved simultaneously. On the basis of the theoretical analysis and experimental verification on the principle with separated optical components, the vertical taper structure, the key part in the whole integrated device was realized, by dynamic etch mask technique. Moreover, the first integrated device of this type was fabricated. A spectral linewidth less than 6 nm and a quantum efficiency of 52.6% have been achieved experimentally.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.440-444
In this paper, the impact of optical beat noise on the performance of optical fast frequency-hopping code-division multiple-access (FFH OCDMA) networks is analyzed. BCH/FFH-OCDMA to reduce the impact of optical beat noise is proposed. It is shown that, BCH/FFH-OCDMA has much better performance under the same bit rate, same chip time and same number of available wavelengths. Another advantage for BCH/FFH-OCDMA is that the code length of one-coincidence sequence will be shorter, which can greatly reduce the difficulty of fabrication for fiber gratings.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.445-448
The propagation of photons through layered tissues is discussed using time resolved Monte Carlo method. The effects of the absorption coefficient, scattering coefficient and anisotropy coefficient on the shape of time resolved transmission are investigated. The energy attenuation of light in layered tissues is also achieved for the infinitesimal-width light and infinite-width light, respectively.
PDF全文 Chinese Journal of Lasers B, 2002年第11卷第6期 pp.449-454