  In a typical optical tweezers detection system, the position of a trapped
object is determined from laser light impinging on a quadrant photodiode. When
the laser is infrared and the photodiode is of silicon, they can act together
as an unintended low-pass filter. This parasitic effect is due to the high
transparency of silicon to near-infrared light. A simple model that accounts
for this phenomenon (Berg-Sorensen et al., J. Appl. Phys., 93, 3167-3176
(2003)) is here solved for frequencies up to 100 kHz, and for laser wavelengths
between 750 and 1064 nm. The solution is applied to experimental data in the
same range, and is demonstrated to give this detection system of optical
tweezers a bandwidth, accuracy, and precision that is limited only by the data
acquisition board's band-width and bandpass ripples, here 96.7 kHz, resp. 0.005
dB.
