A method and apparatus for determining a voltage, such as a bias voltage, supplied by an integrated circuit. The micro-fluid ejection device includes a semiconductor substrate containing a plurality of thermal ejection actuators disposed thereon. A mounting assembly mounts to the positioning device and includes a removable rotation block with a guide hole. The proportional control solenoid valve is connected to a hydrogen supply line and fluidly communicates with a nozzle inlet of the jet pump to control the hydrogen supply to the jet pump. The geometrical foci F1, F2 are separated by a distance SMn, such that a substantially collimated light beam exhibiting a Gaussian type intensity profile propagating along the major axis M and entering the ESIL through the ellipsoidal surface portion converges to a Gaussian beam waist substantially at the second geometrical focus F2.