We propose a convenient, inexpensive technique to monitor the fast early stage of catastrophic optical damage (COD) in 808-nm high-power laser diodes (LDs). Using an optical system based on the 1550-nm laser diode illuminant and photodiode, we measured the facet reflectivity, which gives information about the surface morphology of the output facet with a temporal resolution of 2 ns, allowing us to trace the rapid early COD process in a transient, real-time mode. The formation of the detected 4-μm-long COD damaged area, which caused a local uneven surface at the output facet and a rapid drop in facet reflectivity at 1550 nm from 28% to 2%, was completed within 20–30 ns, 10 ns shorter than that in the longer-wavelength devices.

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This paper presents a method for detecting the heat-dissipation capability of the slow-wave structure (SWS) in a helix traveling wave tube (TWT) using an external heat source. This method utilizes transient temperature rise detection technology and structure function method to nondestructively detect the heat-dissipation capability of SWS. An analytical model is built, and the method is verified by using the simulation tool ANSYS. Furthermore, a dedicated test probe is designed based on this method, and a 2.5-mm diameter helix TWT is measured. The results reveal that the method can effectively detect parts with large thermal resistance in SWS, thereby providing the basis for eliminating the failure products and improving the production process of SWS.