H-BCAM

The H-BCAM is a double-ended metrology camera equipped with four laser diode light sources and two white LED illuminators for retro-reflecting targets. Its field of view is 100 mrad × 75 mrad. Its absolute accuracy with respect to its kinematic mounting balls is 50 μrad rms. Its tracking accuracy is 5 μrad rms across the entire field of view for ranges 80 cm and greater. Its laser positions are known to better than 10 μm rms. The photograph below shows the blue version, which we also refer to as the right-handed H-BCAM. For a photograph of the black left-handed version, see here.

Figure: A Black H-BCAM. We see the front camera lens in a brass holder. On either side are two laser diodes, both turned on for photo. Above and below the lense are the four white LEDs, turned off for the photo. The metalized serial number label is on the lid. The laser safety label is on the other side wall, as shown in this view.

The H-BCAM is one of a family of metrology cameras called BCAMs. We designed the H-BCAM for use in the alignment system of the experiment HIE-ISOLDE, but they have since been used in several other experiments, such as PIP-II

Figure: A Blue H-BCAM. Note the tape covering the mounting hole aperture in the cover. A similar piece of tape covers the lower aperture until we secure the BCAM in place with a screw.

The example in the photograph above has 5-mW laser diodes, and so requires a Class II laser warning label. The location of the lens holder, being flush with the front face of the chassis, implies a focal range of the front camera is 1.5 m. The serial number Q0232 is on the lid, and allows us to look up its calibration constants in the BCAM parameter database.

Figure: A Set of Blue H-BCAMs with Data Acquisition Hardware.

The H-BCAM's powerful lasers are intended for use with retroreflecting sphere targets. A sphere made of glass with refractive index 2.0, such as part number 48-895 from Edmund Optics, acts as a retroreflector, as we describe here. We can measure the position of the sphere by looking at the reflection of an H-BCAM laser using the H-BCAM's camera. The sphere requires no electronics. It can endure cryogenic temperatures. The HIE-ISOLDE alignment of cryogenic modules used such spheres within the modules, seen through sapphire windows by H-BCAMs mounted outside the modules on metal plates.

Figure: A HIE-ISOLDE Cryogenic Module Under Construction. The H-BCAM was designed for use in the HIE-ISOLDE alignment system.

The original H-BCAM, manufactured before 2016, uses two forks to hold the two image sensors, and its chassis is machined out of one piece of aluminum. The two forks are held in place by two screws through the bottom of the chassis. The H-BCAMs manufactured after 2016 have frames screwed to the side walls to hold the CCDs, and the chassis consists of three pieces: a base and two identical flanges for the end walls. Each flange is held in place with four screws.