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Laser & Photo-Medicine Definitions
Frequency
There are three uses of the term ‘frequency’ that can be discussed in relation to laser therapy.
Frequency of Light
The frequency of light is inversely proportional to its wavelength, and is dependent upon the energy value of the individual photons being emitted.
The higher the frequency, the higher the energy, and the shorter the wavelength.
The energy of a photon is calculated by E = hc / wavelength, where ‘h’ is Planks Constant and ‘c’ is the speed of light. The units used for E are called Electron Volts (eV).
eV = 1240 eV-nm / wavelength (nm)
Therefore:
- wavelength is 630nm: 1240 eV-nm / 630nm = 1.97 eV per photon
- wavelength is 780nm: 1240 eV-nm / 780nm = 1.59 eV per photon
- wavelength is 830nm: 1240 eV-nm / 830nm = 1.49 eV per photon
Frequency of Pulsation
The frequency of pulsation describes the rate at which a true-pulsed laser, such as the ubiquitous 904nm, operates.
A true-pulsed laser emits bursts of light at a very high repetition rate. The sum total of all these very short burst of light is the beam. Analogous to a true-pulsed beam is a picket fence, with each vertical paling representing a single burst – or pulse – of light. Typically, the operating frequency of true-pulsed lasers is tens of thousands of pulses per second (Hertz).
Frequency of Switching
The frequency of switching applies to the switching on and off of continuous wave or true-pulsed emissions.
In a monochromatic light beam all the photons will have the same energy value, and therefore wavelength and frequency (and colour, hence the term ‘monochromatic’). However, it is possible – either electrically or mechanically - to turn the light beam on and off a many times a second.
This is generally referred to as switching, and the frequency of switching - the actual number of times the beam is switched on and off each second – is also described using the unit of measure Hertz (Hz).
To produce a switching frequency, a continuous-wave beam can be simply turned on and off rapidly. By ‘continuous-wave’ we simply mean that the beam is of constant amplitude (power) when on.
On the other hand, true-pulsed laser beams are already turning on and off very rapidly, so to switch a true-pulsed laser the train of pulses is interrupted (turned off) a certain number of times a second. Think back to the picket fence, and then imagine the same fence with every fourth or fifth paling removed.
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Contact Details
Australia/New Zealand
| Telephone | +61 2 8215 0687 |
| Facsimile | +61 2 8215 0690 |
| Email | spectra@spectramedics.com |
| Postal Address |
248 Onkaparinga Valley Rd
Oakbank, SA 5243 |
North America
| Telephone |
+1 704 538 7293 |
| Facsimile |
+1 704 538 7781 |
| Email | spectra@spectramedics.com |
| Postal Address |
736 W Double Shoals Rd
Lawndale, NC 28090 |
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