Operating Modes - Novanta vi30 User Manual

OPERATING MODES

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lasers. For more information about the UC- 2000, please consult the UC-2000 Laser Controller
Operator's Manual.
Operating Modes
Tickle pulse
Tickle pulses pre-ionize the laser gas to just below the lasing threshold so that a further increase in pulse
width adds enough energy to the plasma to cause laser emission. Tickle pulses cause the laser to
respond predictably and instantaneously to PWM Command signals, even when there is considerable
delay (laser off time) between applied Command signals.
OEM vi30/40 lasers do not incorporate internal tickle; therefore, users must provide 1μs duration tickle
pulses, at a frequency of 5 kHz, between applied PWM Command signals. A tickle pulse must be sent at
the end of every 200-μs interval in which a PWM Command signal was not applied.
Pulse Width Modulation (PWM)
Pulse Width Modulation, or PWM, controls laser power by varying the duty cycle of the laser's RF
amplifiers, which in turn control the time averaged RF power applied to the laser. Typically, laser output
follows the PWM input with a rise and fall time constant of ~100 μs; however, the laser cannot precisely
follow PWM input signals if the "On" pulse is less than 100 μs in duration. At a constant 50% duty cycle,
vi30/40 lasers typically reach 90–100% of full optical output when operated at a frequency of 5 kHz and
reach 65–80% optical output at 7 kHz. The percentage of optical output increases as duty cycle
increases (at a constant PWM frequency) or as PWM frequency decreases (at a constant duty cycle).
The following figure shows representative vi30/40 optical output waveforms at two different PWM
frequencies.
OEM vi30/40 lasers are designed to operate at Command signal base frequencies up to 100 kHz;
however, the choice of PWM frequency depends on the user's specific application. In many laser
applications, the UC-2000's default Command signal frequency of 5 kHz has proven to work well.
For high-speed motion applications that cannot tolerate any ripple in the optical beam response but
still need adjustable power levels, we recommend the use of higher PWM frequencies, up to 100 kHz
maximum.