Optics - Filter Properties & manipulation of light in flow cytometry

Page
1

Slide 1

Optics - Filter Properties

When using laser light sources, filters must have very sharp cutons and cutoffs since there will be many orders of magnitude more scattered laser light than fluorescence

Can specify wavelengths that filter must reject to certain tolerance (e.g., reject 488 nm light at 10-6 level: only 0.0001% of incident light at 488 nm gets through)

[RFM]

Slide 2

Lecture Goals

This lecture is intended to describe the nature and function of optical systems

It will describe how filters operate

When filters should be used

What problems and issues must be taken into consideration

Slide 3

Optics - Filter Properties

Long pass filters transmit wavelengths above a cut-on wavelength

Short pass filters transmit wavelengths below a cut-off wavelength

Band pass filters transmit wavelengths in a narrow range around a specified wavelength

Band width can be specified

Neutral Density filter is a nondiscriminant intensity reducing filter

Absorption Filter is colored glass that absorbs unwanted light

Slide 4

Optics - Filter Properties

When a filter is placed at a 45o angle to a light source, light which would have been transmitted by that filter is still transmitted but light that would have been blocked is reflected (at a 90o angle)

Used this way, a filter is called a dichroic filter or dichroic mirror

[RFM]

Slide 5

Interference and Diffraction: Gratings

Diffraction essentially describes a departure from theoretical geometric optics

Thus a sharp objet casts an alternating shadow of light and dark “patterns” because of interference

Diffraction is the component that limits resolution

3rd Ed. Shapiro p 83

Slide 6

Interference in Thin Films

Small amounts of incident light are reflected at the interface between two material of different RI

Thickness of the material will alter the constructive or destructive interference patterns - increasing or decreasing certain wavelengths

Optical filters can thus be created that “interfere” with the normal transmission of light

3rd Ed. Shapiro p 82

Slide 7

Optical filters

Interference filters: Dichroic, Dielectric, reflective filters…….reflect the unwanted wavelengths

Absorptive filters: Colour glass filters… absorb the unwanted wavelengths