Q-Switched Laser, What Is It?

If you’ve noticed advertisements for lasers in beauty centers, you may have heard the term “nanosecond laser.” This seemingly professional term is not well-known by many people and they don’t know the difference between this and other lasers.

The nanosecond laser, also known as a Q-Switch Laser, has a Q-Switch as its main component for producing nanosecond pulses. Some people even call these machines “Q machines.” The pulse width of nanosecond lasers is, as the name suggests, in the nanosecond range. Other lasers with longer pulse widths are known as Long Pulse Lasers (LP). Let’s not talk about how to generate such short laser pulses, as it is a matter of physics knowledge. Let’s focus on the difference in the length of the pulses.

As you may recall, laser pulse width (pulse duration) can be long or short and can be measured in milliseconds, microseconds, nanoseconds or even picoseconds. A millisecond is one thousandth of a second, a microsecond is one millionth of a second, and a nanosecond or picosecond is one billionth or one trillionth of a second, respectively. One billionth of a second is an incredibly short time, and it’s difficult to imagine just how short it is. So why do we need such a short pulse width?

The choice of pulse width is mainly determined by the thermal relaxation time of the target chromophore of the organism. In some cases, the thermal relaxation time of the organism is only a few nanoseconds. If we use a pulse width in milliseconds or microseconds to treat it, it won’t be effective. For example, tattoo ink has a thermal relaxation time of only a few nanoseconds, so we can only use a nanosecond laser to treat it.

Some people now use nanosecond lasers to treat other conditions. Is there any benefit to doing so? In general, the thermal relaxation time of pigmented lesions is several milliseconds, so using a pulse width of several milliseconds is sufficient. Nanosecond lasers release laser energy at a nanosecond speed, which can quickly heat up and break down the target, like an explosion happening in the skin. However, this kind of explosion produces shock waves (photoacoustic waves), which can damage the surrounding tissue (photomechanical injury). The effect is very strong, but the side effects are greater than those of long pulse lasers. Many studies have shown that when using lasers of the same wavelength to remove pigmented lesions, nanosecond lasers (755nm Q-Switch vs. 755nm Long Pulse) are more effective than long pulse lasers, but the recovery time is longer and the risk of hyperpigmentation and hypopigmentation is higher. In fact, due to the increasing number of beauty salons offering 1064 Q-Switch Laser at low prices, there are more and more cases of hypopigmentation that are difficult to cure.

Therefore, if you have skin problems, it is best to consult a doctor for a more appropriate treatment plan.