I am using tungsten boat to deposit aluminum thin film for optical mirror applications. I noticed that the visible blue laser light go through the film at thickness of 5000A, 13K A, albeit it is less at 13K A. Is it normal? The evaporation rate is 100A/s.

See the picture below, laser is pointed at the front side, picture taken at the backside. Aluminum at front. thickness 5k-13K Angstroms. Why is light going through aluminum ? What can I do to avoid the transmission.