Output Beam Divergence Research Articles

Focusing of Multimode Laser Beams with Variable Beam Parameters

This paper deals with the focusing of multimode radiation. Two special types of resonator are presented: type 1 produces constant beam radius at varying internal thermal lensing and type 2 has, under some conditions, constant beam divergence. It will be shown that by suitable imaging, a focus of constant diameter and constant position can be realized, if the output beam of the laser is varying in diameter only. Variation of the output beam divergence can be compensated by a different optical system.

Interferometric investigation of a diode laser source

Diode lasers provide a coherent light source in the near IR. They have many desirable characteristics such as small size, high efficiency, a single-longitudinal mode output as large as 15 mW, and can be modulated at high pulse rates. An AlGaAs diode laser operating at 840 nm with an output of 5 mW was evaluated with a Smartt point diffraction interferometer. The wave front observed had astigmatism of ∼2 λ present over the output beam divergence angle. In a modified Twyman-Green interferometer, the coherence length measured was >15 m with high visibility fringes. This source was found to be stable and highly linearly polarized. When used as an interferometric source, many possibilities for small scale interferometers and test equipment are now viable.

Angle constraint for nuclear-pumped X-ray laser weapons

Nuclear-pumped X-ray laser weapons are constrained to have an output beam divergence that is at least as great as a certain minimum value. Because this value is large, such weapons used for ballistic missile defence will require disturbingly high megatonnages in space: for example, a total of ≥ 73 megatons within range of 1,000 attacking missiles, with individual warheads up to 3.7 megatons or higher.

Continuously coupled unstable resonators: problem of large output beam divergence

A problem which arises when one considers continuously coupled unstable resonators is that the beam divergence due to geometrical effects is usually large. This note describes a simple remedy which can be applied in most cases.

Thermal effects in double prism dye laser cavities

Output power, beam divergence, and frequency stability in a double-prism dye laser cavity have been investigated as a function of temperature. For rhodamine 6G dye, it has been found that output power decreases by nearly 34 percent, beam divergence increases from 4.5 to 6.5 mrads, and the laser frequency is shifted by as much as 2 cm-1, for an increase of 10°C above room temperature. The efficiency of the double-prism dye laser oscillator employed here was 18 percent (for N 2 laser pump) at a linewidth of 0.07 cm-1(FWHM). Laser linewidth did not vary in the temperature range investigated here.

Narrow-linewidth tunable ArF* excimer-laser source

The generation of narrow-linewidth tunable radiation from excimer lasers has been a topic of considerable investigation recently.1 Because of the short laser wavelengths generated, such sources are ideal tools for multiphoton spectroscopy in the VUV.2 Because conventional excimer lasers generally operate with broadband laser output and poor beam divergence, ways of Improving the performance of these sources have been sought. Perhaps the most useful technique in this regard is to inject a low level of narrow-linewidth tunable radiation info an excimer laser discharge and thereby make use of the high gain of the excimer systems to amplify the Input beam to high power level. This technique has been used successfully with many of the rare gas halide excimers.1 Experimental complications associated with generating narrow- linewidth readily tunable radiation at 193 nm, however, have made the application of this method to the ArF* excimer, potentially one of the most useful wavelengths for VUV multiphoton spectroscopy, difficult.

Simple method for determining the parameters of singlemode fiber-optic waveguides

An experimental investigation was made of the possibility of using methods of measuring the near- and far-field distributions to determine the core diameter and the difference between the refractive indices of the core and cladding in single-mode fiber-optic waveguides for the near infrared region, by exciting them in a few-mode regime with ultraviolet (λ = 365 nm) radiation. It was found that even for a normalized frequency of V > 4 the output beam divergence corresponded to the numerical aperture of a single-mode optical waveguide, while the half-width of the radiation intensity distribution at the output end corresponded to the core diameter. The accuracy of the proposed method was not inferior to other methods specifically designed for single-mode optical waveguides, but the present method had the advantage of simplicity, especially in the case of a single-mode optical waveguide having a critical wavelength of > 1 μ.

Carbon Dioxide Laser Beam Control for Corneal Surgery

Precise control of output power and beam divergence of a CO2 laser resulted in focused beam diameters down to 25 microns and essentially continuous control of energy deposition on target. Application of controlled laser beams on cow, hog, and human eye-bank reject corneal tissue give evidence of well-defined, narrow cuts. The controllable penetration depth and width of the CO2 laser incisions seem to make the laser an ideal "knife" for such corneal modifications as radial keratotomy and epikeratophakia. Our results indicate that the CO2 laser, when successfully integrated with the standard slit lamp, may be a safer and useful tool in laser surgery of the cornea.

An injection-locked unstable resonator rare-gas halide discharge laser of narrow linewidth and high spatial quality

An oscillator-amplifier KrF discharge laser system capable of providing up to 400 mJ output with 0.1-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> linewidth in a 20-ns pulse is described. The output beam divergence is described and shown to be affected by the discharge current. The output beam is near the diffraction limit in the direction parallel to the discharge and about three times the diffraction limit transverse to the discharge. Operation with XeCl at up to 250 mJ with similar linewidth and spatial quality is also described.

Deep zn-diffused (GaAl)As heterostructure stripe laser with twin transverse junctions for low threshold current and kink-free light characteristics

Deep Zn diffusion at relatively low concentration through the active layer of a highly n-doped (GaAl)As double heterostructure is employed to produce a stripe laser with twin transverse p-n junctions (TTJ's) which provide lateral confinement of both carriers and light in the active layer. Such a structure combines a threshold current of around 40 mA for a 350 μm laser length (minimum measured = 23 mA for 67 μm length) with a near field typically 3 μm wide and an output beam divergence of 6° (both to half intensity).

Optical frequency down conversion in caesium vapour

Experiments are reported in which a pulsed blue-dye laser beam ( omega L) was focused into a heat-pipe oven containing caesium vapour at densities of about 1023 cm-3. Tunable stimulated electronic Raman scattered infra-red radiation ( omega s) was observed together with radiation in the red region of the visible spectrum produced by optical frequency four-wave down conversion: omega R= omega L-2 omega s. Studies of the angular divergence and power of the red output beam demonstrate the importance of non-collinear phase matching in this process.

Optimal output mirrors for laser resonators

To minimize the angular divergence of a laser output beam, the lens effect of the output mirror must be taken into account. The optimum focal length is given for symmetric and half-symmetric resonators, and the dependence of the minimum beam divergence on cavity parameters is shown.

Output coupling for closely confined Pb&amp;lt;inf&amp;gt;1-x&amp;lt;/inf&amp;gt;Sn&amp;lt;inf&amp;gt;x&amp;lt;/inf&amp;gt;Te double-heterostructure lasers

The output coupling of an idealized, symmetric model of a double-heterostructure (DH) laser is analyzed theoretically using parameters suitable to Pb 1-x Sn x Te. For the TE O mode incident at the laser mirror and for thin optical guiding regions such that only the TE O , TE 1 , TM O , and TM 1 modes may propagate, an exact formulation of the coupling problem is obtained including mode coupling at the mirror into the continuum of unguided radiation modes. Using this formulation, the power reflection and transmission coefficients, the fraction of incident power coupled into the radiation modes, the mirror illumination, and the far-field pattern are calculated for typical parameters. Significant mode coupling can occur, limiting the maximum external efficiency of such lasers. This and other potentially undesirable characteristics resulting from close optical confinement, such as large output beam divergence, must be considered in design criteria for DH structures in this alloy system.

Parametric Study of a Helical TEA CO2 Laser

We present results of a parametric study of a helical TEA CO2 laser. The output pulse energy, peak power, pulse shape, and beam divergence have been studied as functions of the capacitance, charging voltage, and gas composition. At 50 kV, with a capacitor of 0.01 μF for each element, we have obtained 3.5 MW output in a 100 ns laser pulse. This study will be of interest to those wishing to use such a device.

Effects of Thermal Lensing in Glass Lasers

Investigations into the influence of thermal lensing on the output energy, beam divergence, emission characteristics, and mode-locking behavior of Nd: glass lasers are reported. The astigmatic effects associated with Brewster-cut rod geometry are considered.

A high-power CO2laser radar transmitter

Experiments on the amplification of CW and pulsed infrared signals at 10.6-μ, wavelength have been carried out on CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser amplifiers excited by dc and pulsed electrical currents. Measurements of low signal gain, gain saturation, repetitive pulse amplification, and optical distortion have led to the design of a 1-kW average power transmitter with 10-μs infrared output pulses. The design, construction, and performance of this device are discussed. Measurements of pulse shaping, pulse-to-pulse stability, output beam divergence, and stability are outlined.