Visibly transparent dyes for through-transmission laser welding

A plastic part in combination with a selected dye for receiving a transmission of a laser beam at a laser welding wavelength, wherein the part includes an upper substrate having a first exterior surface and an opposed first welding surface and further includes a lower substrate having a second exterior surface and an opposed second welding surface, wherein said welding surfaces face each other and collectively define an interior joint region, the part comprising:

• the upper substrate being highly transmissive of the laser welding wavelength;
• the dye being selected to have (i) an absorption band above about 350 nm that includes the laser welding wavelength, (ii) an absorption trough in the visible spectrum, (iii) strong transmission of light within the visible spectrum (iv) an Absorbance Ratio of 1/10, and the dye being disposed in the interior joint region;
• and
• a weld resulting from all pans of the joint region being assembled together and the laser beam being provided and transmitted through said upper substrate to the interior joint region and via vibronic relaxation transmitting heat to weld said welding surfaces together,
• the irradiated dye remaining disposed only within the weld fanned from the first and second welding surfaces.