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This beam shaping assembly can be built into the laser source or placed outside of the laser. 2 See our Understanding and Specifying LIDT of Laser Components application note for more information about the relationship between laser induced damage and Gaussian and flat top laser beam profiles.įlat top beams are not as cost-efficient as Gaussian beams, as an additional beam shaping assembly is required to convert the laser’s output into a flat top beam (Figure 3). The uniform illumination provided by flat top beams is also beneficial for a wide variety of applications, such as fluorescence microscopy, holography, and interferometry. In metrology applications, such as laser induced damage threshold (LIDT) testing, the even and well-defined profile of flat top beams reduces measurement uncertainty and statistical variance. 1 This is beneficial in a wide range of applications where high accuracy and minimized damage to surrounding areas are prioritized. The absence of wings and steeper edge transitions in flat top beams allow for more efficient delivery of energy, as well as a smaller heat affected zone.
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This is determined by dividing the average irradiance value by the maximum irradiance value as described in ISO 13694. One way to evaluate how close a real beam is to an ideal flat top beam is by the flatness factor (F η). Using a Gaussian beam to cut or shape fine features will result in a lower accuracy than that of a flat top beam due to the extended heat-affected zone of Gaussian beams, making a flat top a better option for this type of application. They can also cause damage to surrounding areas and extend the heat-affected zone, which is detrimental in applications such as laser surgery and precise materials processing. The wings of a Gaussian beam often lead to wasted energy if they have an intensity lower than the threshold required for the application (Figure 1). Gaussian lasers are more common and cost-efficient than other lasers, but they have several disadvantages, such as their “wings,” or low intensity regions extending out from the usable central portion of the beam. To learn more about laser modes like TEM 00, visit our Laser Resonator Modes application note.įigure 2: Gaussian and flat top beams at the same optical power, showing the peak intensity of the Gaussian beam is double that of the flat top beam Light goes through a Fourier transform by propagating infinitely far away, or by being focused by a perfect lens. This is because the Fourier transform of a Gaussian function is another Gaussian function. A Gaussian laser beam at the same average optical power as a flat top laser beam will have a peak fluence twice as large as that of the flat top ( Figure 2). Gaussian beams remain constant under transformations therefore, the beam profile is still Gaussian as the beam propagates through the system, even as the beam size varies. High-quality, single-mode lasers produce a low-order Gaussian irradiance profile, the TEM 00 mode. Flat top beams are more efficient in that they surpass the threshold while minimizing wasted energy Gaussian Beams Figure 1: Gaussian beams waste energy through both superfluous energy higher than the threshold required for the application and energy lower than the threshold in the outer portions of the Gaussian beam.