THORLABS M2MS, Operating Manual

Page: 152 / 167

BP209 Series 11 Appendix
Page 150
21424-D02
11.5 Power Ranges
The max. usable input power depends on the beam diameter and the wavelength: the smaller
the beam width the lower the maximum input power because of the maximum power density of
the photodiode. The diagram below shows the allowed input power range at the wavelength of
maximum responsivity (BP209-VIS ~ 980 nm; BP209IR1 ~ 1550nm; BP209-IR2 ~ 2200nm):
Note
Please note that these operating power ranges apply to measurements made using the slits in
scanning-slit or knife-edge mode; these limits may be reduced when measuring total power.
Scanning-slit mode transmits a fraction of the beam power to the photodetector, and during
knife-edge mode the un-attenuated, <Ø20 µm, full beam is transmitted to the photodetector. In
addition to the two pairs of slits, the rotating drum contains an aperture fitted with a neutral
density (ND) filter that, once per rotation, allows the full attenuated beam to reach the photode-
tector. The power in the attenuated full beam may fall outside of the operating range of the de-
tector. In this case, an error message will be displayed in the status box. However, beam shape
measurements using the slits can still be made, assuming the power transmitted by the slits
falls within the limits plotted in the diagram.