Propagation Ratio M2 Research Articles

Measuring laser beam quality, wavefronts, and lens aberrations using ptychography.

We report on an approach for quantitative characterization of laser beam quality, wavefronts, and lens aberrations using ptychography with a near-infrared supercontinuum laser. Ptychography is shown to offer a powerful alternative for both beam propagation ratio M2 and wavefront measurements compared with existing techniques. In addition, ptychography is used to recover the transmission function of a microlens array for aberration analysis. The results demonstrate ptychography's flexibility in wavefront metrology and optical shop testing.

Characterization of High-power DFB-MOPA Diode Lasers Emitting at 1064 nm

Detail characterization of the such laser diode is important for the applications. Electro-Optical and spectral characteristics of the high power 1064 nm DFB-MOPA lasers are investigated at room temperature as function of injection current. Beam quality is characterized by waist diameter and far-field divergence angle versus average optical output power. Beam propagation ratio M2 is defined at difference intensity levels from lateral beam profile giving more detail laser behaviors at high power.

Real-time complex amplitude reconstruction method for beam quality M2 factor measurement.

We present a real-time complex amplitude reconstruction method for determining the beam propagation ratio M2 of laser beams based on the transport of intensity equation (TIE). In this work, a synchronous acquisition system consisting of two identical CCDs is established. Once two beam intensity images at different cross-section positions along the optical axis are captured simultaneously by the system, the complex amplitude of the laser beam can be rapidly reconstructed using TIE algorithm. Then the beam intensity distribution at any section position along its propagation direction can be obtained by using angular spectrum (AS) theory. The beam quality M2 factor is therefore calculated utilizing the second-order moments and hyperbola fitting methods, which conform to the ISO standard. The suitability of this method is verified by the numerical analysis and experiments with the He-Ne and high-power fiber laser sources, respectively. The experimental technique is simple and fast, which allows to investigate laser beams under conditions inaccessible to other methods.

Fast M2measurement for fiber beams based on modal analysis

We report on a fast and experimentally easy technique for measuring the beam propagation ratio M(2) of light guided by optical fibers. A holographic filter enables us to determine amplitudes and phases of the excited fiber eigenmodes. The coherent superposition of modes allows the reconstruction of the optical field. With this information at hand, we are able to simulate the free-space propagation of the beam and to perform a virtual caustic measurement. Associated beam propagation ratios M(2) accurately agree with ISO-standard measurements.

Real-time determination of laser beam quality by modal decomposition

We present a real-time method to determine the beam propagation ratio M2 of laser beams. The all-optical measurement of modal amplitudes yields M2 parameters conform to the ISO standard method. The experimental technique is simple and fast, which allows to investigate laser beams under conditions inaccessible to other methods.

Observe the Beam at the Center of Interest

AbstractFor many laser applications it is essential to focus the beam. The characteristics of the focused beam determine fundamentally the result of the laser process. The key parameters for characterizing a laser beam are: the laser power, the beam width, the beam position, the beam propagation ratio M2, the polarization etc. Measurements at the focus of high power laser are a very demanding task. This article will start with a short review on the techniques to focus a beam. Then we are going to concentrate on different concepts how to realize a practical focus diagnostics. Finally, we discuss some typical results and analyze the relation between cause and effect.

Traceable measurements for beam propagation ratio M2

This paper reports an investigation into measurement techniques and infrastructure suitable for underpinning traceable calibration of devices for beam propagation parameter measurement. The accurate knowledge of the M2 parameter is required for a diverse range of applications including semiconductor manufacture, process control, laser machining, thin-film transistors (TFT), fundamental research into frequency doubling, and the production and characterisation of optical components. Characterisation of the size and position of the beam waist is essential for the correct hazard classification of extended source laser systems using the IEC 60825 series of standards. A system for measuring beam propagation factor measurement has been developed at NPL based on the methodology outlined in the ISO 11146 series of standards. This methodology uses spatial intensity profile measurements of the beam at defined points along the direction of propagation of the beam through a beam waist produced by a convex lens. The beam widths obtained using a CCD and a converging second moment method, are fitted to a hyperbolic propagation envelope and the beam propagation coefficients are obtained from this shape. The traceability of this method has been provided by using graticules calibrated against length standards and carefully measured CCD camera parameters.

High-power 808-nm tapered diode lasers with nearly diffraction-limited beam quality of M/sup 2/=1.9 at P=4.4 W

High-power 808-nm tapered diode lasers mounted as single emitters with very good brightness were manufactured and analyzed. The beam propagation ratio M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is 1.9 at 4.4 W; a very low beam propagation ratio M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 1.3 is achieved at 3.9 W. At 808 nm, the high brightness of 460 MWmiddotcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> sr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> never reported before is a step forward toward new applications of tapered diode lasers

Influences on the beam propagation ratio M2

A beam is described by its transverse power density distribution, its wavefront, and its transverse distribution of coherence. The beam propagation ratio, M 2, is expressed as the square root of the sum of each of the three beam attributes. The shape of the power density distribution governs the diffraction of the beam. The stronger it is modulated, the higher the M 2. In comparison to an non-aberrated beam, the M 2 of a beam with an aberrated wavefront is increased. Similarly, the M 2 of a partially coherent beam is higher than the one of a fully coherent one. A concise formula is derived. The components of M 2 of a mixture of Hermite–Gaussian beams and of a spherically aberrated Gaussian beam are given as examples.

Determination of beam parameters and coherence properties of laser radiation by use of an extended Hartmann-Shack wave-front sensor.

A combination of a Hartmann-Shack sensor and a standard far-field measurement on one single detector is proposed. The technique is fast and operates without movable parts, thus permitting a compact design. It is not only suited for characterization of the wave-front distribution but may also be considered for determination of the important parameters of beam width, beam divergence, and beam propagation ratio M2 of partially coherent laser beams. First results indicate that a fairly thorough beam characterization, including spatial coherence, propagation characteristics, and beam quality, can be achieved with this method.