The gain medium is the aspect of a laser device that will determine the wavelength of laser light emitted. Gain mediums may be solid, liquid, or gas. Lasers used in tattoo removal are solid state gain mediums. The most common wavelength used for tattoo removal is 1064 nm which is produced by the Nd:YAG crystal (Neodymium-doped Yttrium Aluminum Garnet). Other common gain mediums for tattoo removal are Alexandrite (755 nm) and Ruby (694 nm). In order to create 532 nm laser energy, 1064 nm laser emission is passed through a KTP crystal (Potassium Titanyl Phosphate), which serves as a second harmonic generator, cutting the wavelength in half.
Important to note, though, is that gain medium alone won’t determine the function of a laser system. The final component – the Q-switching mechanism – is what determines the function. For instance, attempting to use a Q-switched device to permanently reduce or remove hair will prove ineffective, while using a hair removal device to treat tattoos is dangerous.
Q-Switched lasers produce extremely short bursts of energy. A Q-switched device is capable of producing massive amounts of power instantaneously. This peak power is what plays a role in breaking up the most stubborn inks.
Q-Switched lasers are used for much more than just tattoo removal as well. They can be used to treat pigmented and vascular lesions, nonablative skin resurfacing procedures, as well as toenail fungus. With all of these applications, wavelength selection is critical in treating the malady as efficiently and appropriately as possible.
Types of Q-Switched Lasers
Q-Switched lasers have some pretty significant differences, creating various advantages and disadvantages with each measure.
Active vs. Passive
Actively Q-switched (AQSW) and Passively Q-Switched (PQSW) laser devices are used across the world for their application of tattoo removal, among many other aesthetic procedures. The difference between the two is that actively Q-switched lasers have a more complex pulse production method that allows for greater pulse energy and peak power.
Passively Q-switched lasers are generally less powerful, but more affordable. Technologically speaking, AQSW devices utilize a Pockels Cell to release energy in one single, very powerful pulse, while PQSW devices use a Saturable Absorber which functions similarly but releases energy in a train of pulses. This means that an AQSW device is capable of higher peak power and thus, is more effective at late-stage treatments than a passively Q-switched device.
These lasers are relatively simple to tell apart. AQSW devices are usually large and more than likely have an articulating arm stemming from the top of the system. AQSW systems are usually comprised of 7 optics, as well as some type of handpiece, allowing for a complete range of motion to treat any location on the body. AQSW systems are not portable as they are sensitive to shock and vibration.
PQSW devices are generally smaller, as well as potentially portable. They come in the form of tabletop units or on-a-cart systems, but always have a gun-shaped treatment head attached with an umbilical cord, as opposed to an articulating arm. This cord contains voltage leads for the flashlamp as well as cooling fluid hoses (deionized water, in most cases). PQSW systems are less vulnerable to shock and vibration, but because the energy is released as a train of pulses, they are not as efficient as tattoo removal devices AQSW systems are.
Picosecond vs. Nanosecond
Picosecond devices and AQSW nanosecond devices are much more similar than AQSW are to PQSW devices. One nanosecond is a billionth of a second, and one picosecond is a trillionth of a second. Picosecond systems may be more accurately referred to as sub-nano, quantitatively speaking. Traditional AQSW devices will have a 6-40 nanosecond pulse duration, while picosecond AQSW devices will vary between 500-800 picoseconds – essentially, making the pulse duration 6-10x faster, with equivalent system energy (i.e. .9-1.0 Joules).
The current claim is that picosecond devices can remove tattoos in fewer treatments because the pulse duration is shorter than conventional nanosecond Q-switched lasers. Additionally, the reduction in pulse duration is argued to create less thermal damage, thereby preserving more skin tissue and reducing side effects in the process. The clinical studies performed to research this point have not found picosecond devices to provide a significant statistical difference from the existing nanosecond technology. While a higher peak power is possible with a picosecond device, the point at which this becomes an important aspect in the removal process won’t present itself until potentially after the tattoo may already be removed.