Q-Switched Nd:YAG Lasers
Technology, Applications, and Types of Systems
These lasers are used around the world for their unparalleled ability to target pigment in the skin. Leading dermatology, plastic surgery, and laser specialty clinics value Q-switched lasers for their efficacy for a variety of skin issues, primarily unwanted tattoos. This article will explain the technology behind the lasers, their various applications, and the different types of systems on the market.
When it comes to Q-Switched (QSW) lasers, there are a few key components to discuss:
- The laser
- The gain medium
- The Q-switching mechanism
The word ‘laser’ is an acronym for ‘Light Amplification by Stimulated Emission of Radiation.’ Lasers are monochromatic, which means that photons emitted will be moving at a wavelength (i.e., color) determined by the gain medium. They are also collimated, meaning that in a vacuum, the light beam won’t spread out.
Lasers fall into various classifications, dependent on the power emitted. These classifications vary from Class I (one, or 1), to Class IV (four, or 4). Most lasers used in aesthetics and all lasers for tattoo removal are Class IV laser devices. This means they are the most powerful class of laser, and goggles or patient eye shields are required to be worn for safe use of the device.
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.
There are two elements that make Q-Switched Nd:YAG lasers essential for treating skin conditions:
- The 1064 nm and 532 nm wavelengths can be useful for targeting certain pigments
- The pulse is powerful enough to destroy its target, but brief enough to not harm the skin
This classification of lasers are useful for treating:
- unwanted tattoos
- pigmented lesions (brown spots, age spots, etc.)
- vascular lesions (spider veins)
- toenail fungus
- non-ablative skin rejuvenation
In all of these cases, the QSW Nd:YAG laser is important for the treatment because the laser is able to penetrate into the skin (or nail) without harming it and have the energy absorbed by the target (whether it be tattoo pigment, hemoglobin, melanin, or fungus).
The two different wavelengths are used for different applications, as they are absorbed differently by pigments and chromophores.
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.
Astanza offers a variety of Q-switched lasers for sale. Click here to see them all.
Check out these other resources from Astanza:
- Laser Equipment Buying Guide
- Why Laser Wavelengths Matter for Removing Tattoos
- 10 Critical Questions to Ask Before Buying a Laser
- The Market for Laser Tattoo Removal
- The Astanza Trinity Laser