Shmuel Blit

The formation of laser beams with pure azimuthal or radial polarization

Laser resonator configurations for obtaining pure azimuthal and radial polarized beams are presented. They involve the coherent summation, inside the laser resonator, of two orthogonally polarized TEM01 modes. Basic principles and experimental results with a Nd:YAG laser are presented. The results include a full space variant polarization measurement and show efficient formation of high-quality azimuthal and radial polarized beams.

Efficient conversion of a Gaussian beam to a high purity helical beam

Abstract A method for efficiently converting a Gaussian beam into a helical Laguerre–Gaussian (LG) beam is presented. It is based on using a pair of axicons to produce a shifted-Gaussian (doughnut) intensity distribution that is then passed through a spiral phase element. It is shown that the conversion efficiency can be as high as ∼98%, and the calculated far-field intensity distributions of the output beams are very close to those of corresponding pure LG intensity distributions. The principle of the method, the needed optical arrangement, and calculated and experimental results are presented.

Early termination of flashlamp pumped dye laser pulses by shock wave formation.

The problem of early termination of laser action in flashlamp pumped dye lasers is investigated. It is found that in high power, short pulse duration systems shock waves are created in the dye solution. Index inhomogeneities in the laser medium are created, and these lead to the termination of laser action. The velocity of propagation of the disturbance is measured. Some possibilities concerning the origin of these shock waves are examined. A design scheme that overcomes the effect of the disturbance in short pulse (</=5 microsec) systems is described.

Laser operation with two orthogonally polarized transverse modes

Laser resonator configurations, which enable laser operation with two orthogonally polarized transverse modes, are presented. The intensity distributions of these two modes can be chosen to be complementary, so the gain medium can be exploited more efficiently than with a single mode, leading to improved output power. Moreover, the two modes can be combined and efficiently transformed into a single high-quality beam. Basic principles and experimental results with Nd:YAG lasers are presented.

Effect of phase errors on laser mode selection with binary phase elements

We present numerical and experimental investigations to determine the effect of such surface height deviations of the intra-cavity binary phase elements inserted into an Nd-YAG laser and the selection of the Laguerre-Gaussian (0,1) (LG/sub 01/) and Laguerre-Gaussian (0,2) (LG/sub 02/) degenerated modes.

Efficient formation of pure helical beams from a Gaussian beam

Summary from only given. We verified our approach experimentally with spiral phase elements (SPEs) and a cw Nd-YAG laser. The experimental intensity distribution at the far field when passing the incident shifted-Gaussian beam through SPE was detected by a CCD camera.

Laser operation with two controlled transverse modes

In a laser resonator operating with many transverse modes, the emerging output beam quality is relatively poor. Improvement of the beam quality is typically obtained by inserting an aperture inside the resonator so as to reduce the effective radius of the gain medium, until only the optimal fundamental mode of Gaussian shape exists. Unfortunately, this results in a significant reduction of the output power. It is possible to operate a laser with a single high-order transverse mode by applying intra-cavity elements, such as apertures or phase elements. Such high-order modes exploit a relatively large volume of the gain medium, so the output power is relatively high. However, the intensity distribution of a single high-order mode usually consists of some low-intensity regions, resulting in inefficient utilization of the gain medium, with respect to the multi-mode operation. We demonstrate a novel resonator configuration in which it is possible to select two different transverse modes, each of which has a specific polarization, and can be manipulated separately. The intensity distributions of these modes can be chosen to be complementary, i.e. the peaks of the first mode would fall on the valleys of the second mode. Thus, the gain medium can be exploited more efficiently. This results in an increase in the total output power, yet with better beam quality than with the multi-mode operation.