By using spectrophotometer (Shimadzu SolidSpec 3700) at NAOJ ATC

transmissivity and reflectivity of the reference samples were measured.

From these measurements, absorption value can be obtained.

SURFACE SAMPLE:    Newport FRQ-ND02          22.0%

BULK SAMPLE:            Schott glass  NG-12         37.5%     ---> 37.5% / 0.36 cm = 104% /cm

Both of values are almost consistent with catalog spec. (22.2% and 116% /cm).