Qiang Lin

Space-time profiles of an ultrashort pulsed Gaussian beam

By using a different initial value from the previous treatments, we reveal that the pulsed Gaussian beam in free space can be expressed as a simple wave packet along with the complex time, which gives all the information about the spatial and temporal behaviors of the pulse. Then the space-time profiles of a space-time Gaussian pulse are studied. It is shown that even when the pulse propagates in free space, there exist couplings among the beam parameters in space and time. The spot-size-related couplings enlarge the temporal domain (TD) spatial size of the pulse and lessen the carrier frequency of the pulse of the paraxial points, and the wavefront-related couplings bend the transverse spatial shape of the pulse with the wavefront.

Spectral and temporal properties of ultrashort light pulse in the far zone

The spectral and temporal properties of ultrashort pulses in the far zone are studied by using Rayleigh diffraction integrals. It is shown that the Fourier spectra of the pulse at an observation point in the far zone is different from the spectra in the initial plane. For ultrashort pulses there exists a spectral shift whose magnitude depends on the spectral linewidth, the effective spatial width, and the direction of observation. These results are more similar to that of a partially coherent light beam given by Dacic and Wolf [J. Opt. Soc. Am. A 5 (1988) 1118]. But the spectral shift presented here only arises from the frequency dependence of the propagator that characterizes the propagation of the Fourier monochromatic components of the pulsed field. The shift is remarkable for light pulses with several femtosecond duration, but the pulse shape in the far zone is nearly unchanged.

Spectral shifts of apertured Gaussian Schell-model beam

The spectral shift of Gaussian Schell-model beam passing through a circular aperture is investigated theoretically in this paper. Various factors which have influences on the spectral shift are analysed. The numerical results show that the shift of the spectrum depends on the size of the aperture, the effective correlation length and the spectrum width of the light source. Additionally, the amount of the spectral shift depends on the propagation distance. In the far-field, the spectrum is blue-shifted, while in the near field it is red-shifted under some conditions.

Three-dimensional evolution of ultrashort pulses in dispersive media beyond the slowly varying envelope approximation

A new analytical solution for the three-dimensional evolution of femtosecond pulses in a medium with group velocity dispersion is presented. It is found that for Gaussian pulses as short as a few optical cycles, the coupling between spatial and temporal parameters becomes important, which will cause breakdown of the slowly varying envelope approximation (SVEA) equation.

The far-zone spectral properties of partially coherent light transmitted from a homogeneous dielectric slab

The far-zone spectrum of partially coherent light transmitted from a homogeneous stratified medium are studied. The changes of the far-zone spectrum in the axial and paraxial points are analyzed in detail for the case that a Gaussian Schell model beam transmitted from a homogeneous dielectric slab. It is found that the transmitted spectrum may change in many different ways, such as red shifts, blue shifts, line narrowing and splitting into multiple lines. The parameters of both the incident light and the transmitted medium have a strong influence on the properties of the transmitted spectrum in the far zone.

Laser beam smoothing by rotating random phase plate

A novel method for laser beam smoothing by rotating random phase plate is presented in this paper. A random phase plate for CO2 laser was made, and satisfactory results were obtained. The experimental results coincide very well with theoretical analysis.

Propagation characteristics of chopped light pulses through dispersive media

The propagation characteristics of chopped light pulses with sine amplitude profile through dispersive systems is investigated theoretically by means of temporal ABCD matrix. Solution is obtained by temporal diffraction integral. The results show that the chopped light pulses have a certain non-broadening property under some conditions.

Two kinds of new beam lasers

According to the more complete diffraction theory, a series of new beams was invented both outside and inside laser cavity by using (lambda) /2 phase plate. A new beam with equivalent beam quality factor Me2 less than 1 is achieved on ten-watt CO2 laser and on hundred-Watt and thousand-Watt CO2 laser with axial express flux. It may be named as the first kind of new beam laser. From the point of view of practical applications, we designed and produced a new structure of laser cavity whose output mirror was a special mirror with step reflectivity. We have realized 1000 W new beam on CO2 laser with transverse express flux, which is close to the fundamental mode. It may be named as the second kind new laser beam. Its structure is simpler than others, but it brings excellent results.

Analysis of the properties of self compensation for thermal distortion in a Eckige-Schraube laser

In the present paper, the ray path in a solid state Eckige-Schraube laser is analyzed by the tensor method. The properties of self compensation for thermal distortion and of symmetry in both transverse directions are proved.

Nature of diffraction and its applications

A new suggestion that there is a phase jump of (pi) in the boundary wave is put forward in this paper. This suggestion may be a supplement of Huygens-Fresnel principle. Based on this new suggestion, a series of new beam was invented, both outside and inside laser cavity. Especially, a new CO2 laser with equivalent beam quality factor M2e < 1 is achieved. It can be considered as the result of some controllable nonlinear self-focusing, and the physical background of deformed quantum mechanics.