Part 2: Teardown of the laser scanner module from a Fujifilm FCR XG-1 x-ray image scanner / digitizer. Also known as Computerized Radiography (CR), it fulfills the job of scanning a x-ray exposed image plate. It uses a laser beam to extract each pixel illumination with a photo multiplier tube setup. It can scan 72 plate per hour with a maximum resolution of 7080 X 9480. In 12 bits per pixel gray scale.
Fuji’s photostimulable phosphor is deposited on a flexible polyester film support with grain size about 5 micrometers. It is described as “barium fluorobromide containing a trace amount of bivalent europium as a luminescence center”. Europium is a divalent cation that replaces barium to create a solid solution. When Eu2+ ions are struck by ionizing radiation, they lose an additional electron to become Eu3+ ions. These electrons enter the conduction band of the crystal and become trapped in the bromine ion empty lattice of the crystal. The resulting is a metastable state that is higher in energy than the original condition. A lower-frequency light source that is insufficient in energy to create more Eu3+ ions can return the trapped electrons to the conduction band. As these mobilized electrons encounter Eu3+ ions, they release a blue-violet 400 nm luminescence. [wikipedia]
Inside the laser module there is a laser diode to the right, rotating mirror in the middle, output lenses and a receiving sensor to the left. The laser light path is illustrated with red lines for the 633 nm red laser and the green lines represent the start of line of a new scan. Pink is the feedback from the laser diode to its own power supply / control.
The laser diode sits in a holder that has two adjustment screws and has a port to adjust focal point of the lens that sits inside the housing. The PCB also has a photodiode for feedback of the laser intensity.
The rotating mirror is a polygon scanner motor. Which is a polished metal surface sitting on top of a high speed / precision fluid bearing motor.
The output lens has a clear blue filter coating in all places but the corner that corresponds to the light path that goes to the receiving sensor mirror and optics in the left side of the module.