When the laser gain medium is driven three times harder for a short period of time, the optical output can be three times higher than during normal Continuous Wave (CW) operation. This mode of operation, and the technology that enables it, is called Super Pulse (-P). In laser applications such as surgery, marking on glass and ceramic, and cutting thin metal foils, the abbreviated processing time of a high-energy pulse vaporizes the material faster and more efficiently. The resultant material finish reduces charring, cracking, burning, and debris. Super Pulse improves results in surgery, making procedures become more effective by reducing both pain and healing times.
Optimizing the Pulse Parameters for Super Pulse Operation
Typically in CO2 lasers, the optical response is slower than the electronic control signal, due to the transfer and release of energy commonly referred to as rise and fall time. The laser power will not rise instantaneously to its peak when the on command is issued, nor will it drop to zero immediately after the off command, as can be seen on the scope traces below. Therefore, to maximize pulse energies, the electronic laser pulse control signal should be somewhat longer than the rise time. For ALC products this is typically around 100μs. Super Pulse (-P) is best when used at fixed pulse-repetition frequencies and duty cycles to maintain uniform pulse lengths.
In waveforms A and B shown above, the upper blue trace is the command signal and the lower yellow trace is the laser pulse train. The longer pulse on the left has enough time to achieve peak power, but it is at a low frequency. Although the shorter pulse on the right does not achieve the highest possible peak power, it’s still very useful in many applications requiring a fast pulse train. Whatever the application-specific requirements are for your team, Access Laser can optimize our products to match your laser pulse parameters.
How to Vary Pulse Width and Frequency
All the Access Laser products have a BNC port on the RF driver where you can supply your own pulse signal at a wide range of frequencies and pulse lengths. A general-purpose pulse generator or function generator can be used to supply this variable signal. Zero volts will turn off the laser, and five volts will turn on the laser. The laser controllers from Access Laser provide a knob for pulse width control at a fixed frequency: 2.5 kHz, 5 kHz or 16 kHz can be specified.
For a Super Pulse (-P) laser, the pulse length is typically limited to 400μs, and the duty cycle to 30%. A Super Pulse (-P) laser will not operate in the CW mode. However, lasers enabled with the Dual Drive (-D) technology can perform in either CW or Super Pulse (-P) modes based on the DC supply being used to drive the RF. Its average power is typically lower than its CW counterpart. For these reasons, some applications that require high average power rather than high energy pulses will not benefit from this mode of operation.