4) The number one reason these lasers are sold is because of price and incredible marketing.
Read this article below from some of the most respected researchers in the laser industry. They also have one of the best book for practitioners with compiled clinical study research on laser therapy called the New Laser Therapy Handbook.
Pulsing and Super Pulsing: A Commentary
By Jan Tunér, DDS
Lars Hode, DrSci (Swedish Laser Medical Society)
There are principally two types of pulsing in laser phototherapy
• chopped (switched) or
• super pulsed
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 200 nanoseconds 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.
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 emit 10-100 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.
A Serious Problem
One manufacturer, for example, promotes its super-pulsed lasers as having 25,000 mW or 50,000 mW of power, and offers the user a small number of preset ‘programs’ which, essentially, only adjust the pulse frequency and, therefore, the average output power. One of these ‘programs’ sets a frequency of 5 Hz.
To calculate the average power one must only know the Peak Power, the Pulse Frequency and the Pulse Duration.
As mentioned previously, the pulse duration (i.e., the ‘width’ of each pulse of energy) of most GaAs devices is 100-200 nanoseconds (0.0000001 – 0.0000002 sec).
If we use the manufacturer’s ‘highest’ power option (50,000 mW), select their 5 Hz program, and assume the longest possible pulse duration (0.0000002 sec) for our calculation, we arrive at an Average Output Power of only 0.050 mW, or fifty millionths of one Watt.
With this very low average power it will take twenty thousand seconds (5.6 hours) for this manufacturer’s laser to deliver one Joule. Impractically long, perhaps?
Other super-pulsed lasers employ “pulse trains”, which enable the average output to be maintained at a constant level over all frequencies. The importance of checking upon this is obvious when it comes to acquiring a GaAs laser.
False Super Pulsing
One manufacturer claims that its dual-wavelength (800 nm and 970 nm) high-powered Class IV laser has better penetration due to its ‘Intense Super Pulse’ emission.
However, these diode lasers are not super pulsed, they are “chopped”, and chopping does not offer increased penetration.
In this case chopping the output simply reduces the tissue-heating effect of the high power laser by both reducing the average power and also allowing time for the tissue to thermally relax (i.e., dissipate heat) between each pulse of light.
The biological differences between super-pulsed and chopped emissions are likely to be
fundamental. Is pulsing then of interest? The in vitro studies by e.g. Tiina Karu clearly show that the type of pulsing is of importance. However, in these situations one type of cell and one type of reaction is studied. In the clinical situation, many types of cells are irradiated and a multitude of events happen. So is pulsing then of any clinical importance?
The answer is that we do not know. This is well presented in the recent literature review by Hashmi et al, http://www.ncbi.nlm.nih.gov/pubmed/20662021.
Some lasers are pulsed to allow for heat dissipation, but that has nothing to do with biostimulation. Chopping is an option in some continuous lasers and users should be aware of the fact that suggested pulse repetition rates are only setting options; we do not know if the different pulse repetition rates provide different biological results.
Many “recommended” frequencies employed in therapeutic lasers are, in fact, carried over from other fields and modalities, especially electrical stimulation.
Nogier’s frequencies, for example, are often incorporated into laser therapy protocols for both humans and animals; yet their original application was in humans only, specifically auricular therapy delivered by electrical stimulation.
Due largely to the impact of pulse frequency upon the average power of the first therapeutic diode laser, the GaAs, Nogier’s original frequencies (there are seven, ranging from 1.14 Hz to 146 Hz) are even presented at a higher “harmonic” so as to achieve a higher average output power, further increasing the disparity between their original intended application and their current use.
Despite this, and the fact that there have been no studies undertaken to compare or confirm the efficacy of the original or higher-harmonic laser-delivered frequencies in humans or animals, these and other frequencies are provided as an integral part of many different therapeutic laser devices and their pre-programmed protocols.