Laser Thearpy: Continuous mode VS Pulsed or Super Pused
Pulsing
There are principally two types of pulsing in laser photo therapy
- chopped (switched) or
- superpulsed
A chopped beam is a continuous beam that is electronically (or mechanically) switched between on and off.
During the moments when it is on it has typically the same output power as in continuous mode, but as it is not on all the time, the average output power is less than when it is continuous.
The average power is a function of the continuous wave power and the duty cycle (the ratio of the “on” time of the beam to the total emission (“on” + “off”) time, usually expressed as a percentage).
Typical laser types are most of the gas lasers (such as the HeNe laser) and all
semiconductor (diode) lasers (except the GaAs laser). The GaAs laser was the first semiconductor laser in the world. In order to generate laser light, the current density in the GaAs semiconductor crystal had to be extremely high. As a consequence of the high electric current the output power of this semiconductor laser is very high.
Typical peak power is in the order of many watts. However, when an electric current is conducted through a material heat is generated, and with the necessary high current in this laser the crystal will burn up immediately unless the time of current conduction is extremely short, i.e., super-pulsed GaAs lasers cannot work continuously.
The maximal pulse time for this laser is in the order of 100 to 200nanoseconds and, after each such pulse, a long cooling time is needed, usually about a thousand times longer than said pulse time.
This form of pulsing is called super pulsing and, although the peak power is very high, the average output of super-pulsed lasers is comparatively low. Typically the GaAs laser produces its maximum emission at 904 nm.
What About Average Power Output
Restating the above, even though the peak power of the super-pulsed GaAs laser may be very high,it lasts for an extremely short time compared to the pulse cycle, resulting in an average output power that is usually a thousand times lower than the peak power. For clinical use, it is the average power that counts
Lucien
Sales manager
The energy (dose) delivered from pulsed lasers is always the average output power multiplied by the exposure time. The average power is the important output of the laser.
Some manufacturers prefer to label these lasers as “very strong” and state only the peak power which then can be in the order of 100 watts.
This sounds impressive, but typically these lasers emit10-100 mW average power, and this is what counts for the treatment.
The GaAs lasers are quite useful in physiotherapy, but care has to be taken.
In some super-pulsed lasers the average output changes with the set pulse frequency, so that low pulse repetition rates deliver very low average outputs.
This means that with such lasers, with low frequency settings, the treatment time may be impractically long in order to deliver a reasonable dose.
More info:
www.gigaalaser.com
lucien@gigaalaser.com
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