Optics Chamber

The optics chamber (or box) contains the dichroic mirrors, filters (excluding the laser clean-up filter), and light detection elements.  The optics cuvette mounts directly to the front of the box and is held in place by a clamping block.  This block is light tight, allowing only light from the laser to enter the box via a telescoping tube.  The schematic diagram shows the direction of the light path from the optics cuvette (drawn in red shading) to the PMTs.  The relative distances between each of the components are indicated.
 
 

Optics Path Diagram

The optics box, cuvette clamp, filter holders, and dichroic mirror mounts are fabricated from black delren for ease of machining and opaqueness.  Photographs of the optics box are shown below where red arrows indicate the direction of the light path (panel A) and the direction of fluid flow is shown with yellow arrows.  The box assembly is mounted on standard ball slides, allowing alignment only in the horizontal direction.  The laser (hidden behind a white plastic partition that acts as a splash guard) is mounted perpendicular to the box on adjustable legs, allowing alignment only in the vertical direction.  The laser clean-up filter (488/10 nm) is housed in a telescoping tube assembly mounted directly on the front of the laser.  No beam steering optics are required.
 

 Optics chamber and cuvette

 

The alignment procedure begins by fixing the height of the laser to the optical axis of the box.  Then, with the optics cuvette mounted to the box, the box assembly is adjusted until the collection tube is in the center of the laser beam.  With the dichroic mirrors removed, the lenses are aligned until a projection of the collection tube if formed on the front surfaces of the PMT’s.  In our present configuration, the projected image is about sixteen times larger than that of the tube I.D..  Filling the collection tube with a diffusing liquid, such as diluted milk, and placing a piece of white paper in front of the PMTs, is helpful in observing the projected image.  Note that a part number for the light collection lens has been omitted from our parts list.  The lens we are using came from a colleague who unfortunately does not have that information.  However, the lens has the physical appearance and properties of #01LAG000, Melles Griot Optics. 

Some readers more familiar with optics have probably noticed the absence of any stop or slit in the image plane.  A crude slit was fabricated for this project, but found to be difficult to align, and not very effective.