Measuring sealing degree of welded glass substrates after ultrafast laser microwelding

In the laser welding (sealing) of transparent materials such as glass, it is necessary to place a light-absorbing material (intermediate layer) between the materials to be welded. However, femtosecond lasers can weld transparent materials without an intermediate layer due to nonlinear absorption phenomena. Using this welding method with ultrashort laser pulses, we measured the sealing degree of the welded glass substrates. As a result, sealing was confirmed for more than one week for the sealing conditions used in this experiment. The internal stresses in the sealed substrates were then measured by the crossed-nicol method. Stresses were concentrated near the welding area, indicating that the welding was successful. Furthermore, Raman spectra were analyzed using a Raman microscope. The change in Raman spectra confirmed that stress was applied to the substrates. This may allow the measurement of welding strength and sealing degree by the change in Raman spectra. By analyzing the welding conditions under different conditions in the future, we can summarize the minimum welding conditions that can be used for sealing.