Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The authors of the recent paper titled “SESAM‐free mode‐locked semiconductor disk laser” [1] make the claim that Kerr lens mode‐locking has been observed in a SESAM free semiconductor disk laser. However, the data presented in the manuscript at best weakly support the central claim that this laser is mode‐locked and at worst are simply the characterisation of a continuous‐wave (CW) laser. The physical principles of mode‐locking are clearly defined in many text books as well as in the first paper reporting mode‐locking [2] and more recently the work of H. A. Haus [3]. When reporting a new mode‐locking technique for a particular class of laser, it is essential to pay detailed attention to the measured characteristics. It is also helpful to comment on the strength of the mode‐locking mechanism. In this case, for example, the effective Kerr lens could be calculated, or better, experimentally measured, to further support the central claim.</jats:p>