Fundamental Laser Mode Research Articles

Laser beam profile shaping with interlaced binary diffraction gratings

A new CO(2) laser beam profile shaper was designed and tested. With high-power efficiency, it transforms a fundamental mode laser beam profile into a flattop profile at a focal plane. The shaper uses an interlaced binary diffraction grating that modulates the E field both in phase and amplitude and generates an apodized and clipped sinc(x) distribution in the object plane.

Recent Developments in Fiber Optic Devices

The advent of the fundamental transverse mode laser diode and low loss optical fiber has extended the wavelength range for communication systems into the optical spectrum region. The indispensable elements for the optical communication systems are light source, transmission medium, and detector. Recent developments in this area in Japan, with particular emphasis on the fundamental transverse mode laser diode and low loss quartz optical fiber, are reviewed.

Properties of diffused PbSnSe homojunction diode lasers

The properties of diffused PbSnSe homojunction diode lasers based on the confinement of injected carriers and of light in the fundamental transverse laser mode are investigated both theoretically and experimentally. The electrostatic potential profile near the graded junction is evaluated for the strongly forward biased case. Resulting injection and gain profiles are narrow and their widths increase with temperature. Free carrier dispersion leads to an optical confinement. From the threshold condition for the TEM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</inf> mode, the threshold current density is obtained, assuming a minority carrier lifetime of 2 ns. PbSnSe diode lasers were fabricated by diffusion of cadmium under different conditions. Experimental laser properties for different junction gradings are discussed in terms of the model. Threshold currents and output powers as a function of temperature, as well as maximum operating temperature and mode behavior, are consistent with the theoretical expectations.

Very low threshold visible TS lasers

Fundamental transverse mode lasers with very low threshold currents have been realized by use of the modified terraced substrate (TS) geometry. The threshold currents of 250 μm cavity length lasers at room temperature are typically 20-30 mA for wavelengths around 750 nm. In the 710 nm laser, which is the shortest lasing wavelength in this work, the threshold is as low as 70 mA in CW operation. The 726 nm laser was operated for only 150 h, while a lifetime longer than 10 000 h is expected for TS lasers with a lasing wavelength longer than 750 nm.

Investigations on laser welding

A welding method has been developed that makes use of fundamental mode laser pulses. These pulses show single-mode relaxation oscillations with a high peak power first spike causing breakdown of the material surface. The laser emission following the first spike can be adapted to the welding requirements and the material properties. Metallurgical problems of intermixing of dissimilar materials in the weld puddle have been investigated with an electron beam microprobe analysis. In the case of materials which normally show bad weldability uniform welds with maximum strength could be achieved by local addition of welding agents to the weld puddle. The lap weld of a stainless-steel spring with a nickel-iron baseplate has been performed with Nb as welding agent.

ANALYSIS OF LENSLIKE EFFECTS IN GAS LASERS

The optical cavities of general curved-mirrors with a negative lenslike medium are discussed, and used to analyze the thermal lensing effects in gas lasers. The mode analysis is made for a CW CO2 laser of a plane-concave cavity. It is shown that the thermal lensing effects have considerable influence on the output and resonance frequencies, particularly for the fundamental mode lasers. Finally, possible thermal lensing effects in ion gas lasers and other lasers are briefly discussed.

Fundamental Mode YAG:Nd Laser Analysis

The condition that limits the volume that will sustain fundamental mode operation in a YAG:Nd laser has been determined. The relationship between the pump lamp power and fundamental mode power has been derived which correctly predicts the single mode power. The analysis incorporates the results of a computer analysis of the laser rod, which, among other things, computes the heat absorbed per unit volume and plots the isotherms for the interior of the rod. Recommendations for the design of high power, fundamental mode lasers are given.