Pellicle beamsplitters are ultra-lightweight components that virtually eliminate multiple reflections commonly associated with thicker glass beamsplitters. Pellicles are manufactured by stretching a 5 µm thick polymer membrane over a flat metal frame. The extreme thinness eliminates secondary reflections by making them coincident with the original beam. Multiple wavelength versatility is an added benefit of an ultra-thin reflective membrane.

Coated pellicles provide equal reflectance and transmission over the same range by means of a neutral, partially reflective coating. The R/T curves below show average values, eliminating the often confusing sinusoidal oscillation due to interference. A ±5% wavelength dependent oscillation is superimposed on all curves.

Vibration Effects
The extreme thinness of pellicles provides many advantages in reducing losses and ghost images. However, the polymer membrane can resonate due to vibrations in the environment. Stiff posts or riser blocks should be used in mounting pellicles to an optical table. Applications subject to air currents or acoustical noise should use glass beamsplitters.

Interference Effects
Interference effects due to thin membranes should be considered when using pellicles. Monochromatic interference between the front and back surfaces can introduce unwanted fringes into a transmitted or reflected beam. Secondly, pellicles act as low finesse interferometers. Over any wavelength range, a ±5% sinusoidal oscillation is superimposed on the transmission and reflection graphs. The oscillation values change very rapidly with wavelength and averages to the values are shown below.