This paper presents the effects of M2 (M square) factor of the laser source on steel materials in terms of spot size, duration of exposure and power density. Generally, laser sources are modelled as a Gaussian beam. M2 factor is known as the beam quality factor and it represents the degree of variation of a laser beam from an ideal Gaussian beam. It determines how well a laser beam will focus or diverge. According to ISO 11146-1, M2 is defined as BPP (Beam Parameter Product) divided by λ/π. It is also related to beam waist and divergence angle. A perfect beam would be a single mode TEM00 laser beam. Single mode fibers have smaller core diameter. It means that it can focus more easily than multi mode fiber laser can. In this study damage effects of CW lasers, which have 1070 nm wavelength, on 1 mm thick steel target plate are examined. Effects of using two different M2 values at different output powers are investigated experimentally and the results are discussed. These results will help compare the theory with experimental results.
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