With the continuous upgrading of diode laser hair removal machines, the diode laser power has become higher and higher, from 500W to 800W, and then to 1200W. But the energy density has not increased significantly. Why?
Frequency, Pulse Width, Energy Density
Before explaining this question, let’s take a look at what frequency, pulse width and energy density are?
(1) Frequency (Hz): the number of times light is emitted in one second;
(2) Pulse width (ms): the time for each light emission;
(3) Energy density (J/cm²): energy per unit area;
In order to facilitate understanding, I hand-painted a picture:
Technical Parameter List Of Diode Laser Hair Removal Machines
Then, let’s take a look at the key technical parameter list of diode laser hair removal machines:
So, the question is, why does the laser power increase, but the energy density does not increase?
The main reason is that due to the increase of diode laser power, the heat generated per unit time will increase sharply (E = P×t). In order to prevent the laser from being burned out, the diode laser stack manufacturer has made the strict restrictions on diode laser stack parameters (laser power and duty cycle, etc.).
Therefore, diode laser hair removal machine manufacturers cannot rely solely on their own performance when designing the hair removal machine. We must design machines in accordance with the parameters of diode laser stack; otherwise, the diode laser stack’s lifespan will be shortened or burned out, which is not covered by the diode laser stack manufacturer’s warranty.
Can You Show Me The Limiting Parameters Of The Diode Laser Stack?
For example, 1200W laser usage parameters (maximum duty cycle 20%), as shown in the figure below:
As can be seen from the figure above:
When the frequency is 1Hz (period T=1000ms), the maximum pulse width is 200ms;
When the frequency is 2Hz (period T=500ms), the maximum pulse width is 100ms;
… …
What Parameters Are Specified By The Laser Manufacturer That Limit The Energy?
From “energy = power x pulse width (E = P×t)”, it can be seen that when the laser power increases, the parameter that limits the increase in energy is the pulse width, and the maximum pulse width of the laser is determined by the maximum duty cycle of the laser.
What Is The Duty Cycle?
The duty cycle refers to the ratio of the light emission time to the total time in a pulse cycle.
Example: The frequency is set to 1Hz, that is, light is emitted once per second, 1 second=1000ms;
(1) For 500W lasers, the manufacturer stipulates that the maximum output duty cycle is 40%, which means that the maximum pulse width is 400ms;
(2) For 1200W lasers, the manufacturer stipulates that the maximum output duty cycle is 20%, which means that the maximum pulse width is 200ms;
(3) For 2000W lasers, the manufacturer stipulates that the maximum output duty cycle is 12%, which means that the maximum pulse width is 120ms;
In summary, according to “energy = power x pulse width (E = P×t)”, although the laser power has increased, the maximum pulse width has decreased, and all the overall energy has not increased significantly.
Since The Energy Density Has Not Increased, Why Pursue Higher Diode Laser Power?
We know that hair removal is a process of energy accumulation, that is, when energy accumulates to a certain extent under a suitable energy density, the hair follicles will be destroyed and the hair will lose the ability to regenerate, so as to achieve the effect of permanent hair removal.
The higher laser power and narrower pulse width can effectively reduce the pain of hair removal, improve the comfort experience, and further improve the hair removal effect.
Finally you will find:
If the energy density of the diode laser machine has adjusted to the maximum and the pulse width still can be adjusted arbitrarily without limitation, then the parameters of this machine are probably fake, because it is unscientific!
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