Why is red tattoo colour badly removed by laser?
Red tattoo ink is not the problem — the 532 nm tip of compact lasers is: a poorly positioned KTP crystal converts only a few percent of the 1064 nm energy.
A common myth about the red colour
There is a myth that the red tattoo colour is very poorly removed by compact lasers. And the reason for this is quite objective. Let’s break it down.
The technical side of the process
In order to remove red pigment from the skin, the 532 nm wavelength of nanosecond compact lasers for tattoo removal should be used. However, the 532 nm wavelength is not native, but is obtained by conversion from the 1064 nm wavelength. This conversion is performed by the crystal in the 532 nm tip that is screwed onto the handpiece of the compact Nd:YAG laser.
| Laser | Wavelength, nm |
|---|---|
| Excimer | UV range (value not shown) |
| Argon | 488–514 |
| KTP | 532 |
| Dye laser (Color.) | 577–630 |
| Ruby | 694 |
| Alexandrite | 755 |
| Diode laser | 800–810 |
| Nd:YAG | 1064 |
| Holmium | 2100 |
| Er:YAG | 2940 |
| CO2 | 10,600 |
Ranges: UV — below 400 nm (UVC 100–280, UVB 280–315, UVA 315–400); visible — 400–750 nm; infrared — above 750 nm.
Which colour will an Nd:YAG laser remove?
Pick a pigment colour — an Nd:YAG laser has only two wavelengths: 1064 and 532 nm.
A simplified scheme based on the article on which colours an Nd:YAG laser can remove.
The 532 nm wavelength conversion problem
And the whole paradox is that how well this crystal converts the 1064 nm wavelength to 532 nm depends on the size of the crystal, its quality and, most interestingly, its position relative to the main Nd:YAG crystal inside the handpiece. And this is where most of the problems occur, because most lasers are made in China, and it all depends on how responsible the manufacturer was in preparing their laser for sale. Ideally, when the tip is fully screwed on, the crystal (it is called the KTP crystal) gets into a perfect position relative to the main crystal and provides optimal conversion to the 532 nm wavelength. But in a large number of lasers, this position is far from ideal. And as a result, the energy that is converted to the 532 nm wavelength will simply be minimal. It will be literally a few percent of the 1064 nm energy. Accordingly, the energy at the 532 nm wavelength will be minimal: maybe 5–10 millijoules or less. With that kind of energy, a good intense effect on the red pigment is out of the question. So the point here is not that the red is poorly removed, but that most compact lasers of very poor quality have a 532 nm wavelength with practically no energy in it.
The solution to removing the red colour
And if the same red pigment in a tattoo is treated with a stationary laser, it will be removed just fine. So it’s not about the pigment, it’s about the quality of 1064-to-532 nm wavelength conversion in a particular laser.
Frequently asked questions
Why is red tattoo ink hard to remove with a compact laser?
Red pigment is treated at 532 nm, which compact Nd:YAG lasers get by converting 1064 nm in a KTP crystal in the tip. If that crystal is poorly positioned, only a few percent of the energy is converted, maybe 5–10 mJ or less, which is too little to affect red pigment.
Can a laser remove red tattoo ink?
Yes. The same red pigment treated with a stationary laser is removed just fine, so the problem is not the pigment but the quality of 1064-to-532 nm conversion in a particular laser.
