Lasers beams with a specific intensity profile such as super–Gaussian, Airy or Dougnut-like are desirable in many applications such as laser materials processing, medicine and communications. We propose a new technique for laser beam shaping by amplifying a beam in an end-pumped bulk amplifier that is pumped with a beam that has a modified intensity profile. Advantages of this method are that it is relatively easy to implement, has the ability to reshape multimode beams and is naturally suited to high power/energy beams. Both three and four level gain materials can be used as amplifier media. However, a big advantage of using three level materials is their ability to attenuate of the seed beam, which enhances the contrast of the shaping.
We first developed a numerical method to obtain the required pump intensity for an arbitrary beam transformation. This method was subsequently experimentally verified using a three level system. The output of a 2.07 μm seed laser was amplified in a Ho:YLF bulk amplifier which was being pumped by a 1.89 μm Tm:YLF laser which had roughly a TEM10 Hermit Gaussian intensity profile. The seed beam was amplified from 0.3 W to 0.55 W at the full pump power of 35 W. More importantly, the beam profile in one transverse direction was significantly shaped from Gaussian to roughly flat-top, as the model predicted. The concept has therefore been shown to be viable and can be used to optimise the beam profile for a wide range of applications.
We propose a new technique for laser beam shaping namely the reshaping of the laser beam into a desirable beam profile by the use of a laser amplifier with a pump beam that has a modified intensity profile. We developed the analytical formula which describes the transformation of the seed beam into the desired beam profile in the amplifiers small signal regime. In the case were high pump power saturated the laser crystal we have shown the method of reshaping of the seed beam into desirable beam by a numerically obtained pump intensity profile. The method can also be extended for shaped seed beams with fixed profile pump.
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