low and compact profile without resort to costly and complex beam steering optics the particular tilt of the spin axis 44 is preferably at an angle u03b1 of 33 degrees from the horizontal other tilt angles may be achieved depending upon the optical characteristics that are particular to the design of the stationary grating 52 and the hologon disc 40 other aspects of the bearing design may be determined according to the particular application and as known in the art accordingly further description of the preferred embodiment will be directed to a novel pretreatment of the bearing surfaces 46a 46b that serves to significantly extend the start stop life of the system 10 to well over 20 000 cycles during the development of the preferred embodiment of the system 10 it was discovered that the catastrophic failures of various prototype air bearings were largely attributable to several factors the major factor appears to be the occurrence of momentary touchdowns of the rotor assembly during acceleration from the rest state to the operating state and during deceleration back to the rest state the momentary touchdowns are believed to occur due to certain modes of instability that are excited as the bearing passes through these transitional states also external vibrations are believed to be coupled to the rotating bearing thus disturbing its spin axis and or inducing a momentary mode of instability a second factor is the tilt of the spin axis which accentuates the radial load on the air bearing and aggravates the impingement of the bearing surfaces during pre liftoff and post touchdown rotations of the rotor assembly also the momentary touchdowns are believed to be more prevalent in the illustrated embodiment due to the tilt of the spin axis touchdown of.