Key facts
- Picosecond pulse
- About one trillionth of a second; pigment is fragmented mainly by a photoacoustic (pressure) effect
- Nanosecond pulse
- About one billionth of a second; Q-switched lasers fragment pigment with more photothermal (heat) contribution
- Shared wavelengths
- 532 nm for superficial pigment, 1064 nm for deeper pigment and darker skin; both exist in pico and Q-switched form
- Used here
- T2 Frax Radiance on the DEKA TORO: 785 nm picosecond, with 532 and 1064 nm nanosecond emissions on the same platform
- Main risk in both
- Post-inflammatory hyperpigmentation when energy, interval or sun exposure is wrong for Fitzpatrick III to V skin
- Melasma
- Treated conservatively, if at all, on either pulse width; heat is a trigger
What is the difference between a pico laser and a Q-switched laser?
The difference is how long each pulse lasts. A pico laser delivers energy in picosecond pulses, about a trillionth of a second; a Q-switched laser delivers nanosecond pulses, about a thousand times longer. Both aim at melanin, both are commonly built at 532 and 1064 nm, and both fragment pigment particles so the body can clear them. The pico laser page describes the three modes used here: spot treatment, low-energy toning and fractional delivery.
Pulse width changes the mechanism. When a pulse is shorter than the time the pigment particle takes to pass heat to its surroundings, the particle is shattered by a pressure wave, a photoacoustic effect, with little heat spreading outward. A longer nanosecond pulse heats the particle and some of the skin around it, a photothermal effect, and that spread of heat is what inflames the surrounding tissue. Q-switched is the older generation; pico is the newer one. Neither is a brand, and neither is a treatment plan.
Why does pulse width matter for PIH risk in Asian skin?
Because inflammation is what drives post-inflammatory hyperpigmentation, and heat is what inflames. In Fitzpatrick III to V skin, the range that covers most patients in Singapore, more melanin sits in the epidermis to absorb stray energy, and melanocytes respond briskly to injury by making more pigment. A pulse that leaves less heat behind leaves less of that stimulus, which is the mechanistic case for the picosecond laser in this population and the reason it is often the first choice for discrete spots in darker skin.
It is a difference in delivery, not a promise. Fluence, spot size, wavelength, the number of passes and the interval between visits still decide how much heat a treatment leaves in the skin, and a picosecond laser set carelessly can darken pigment as surely as a nanosecond one. The guide to pico laser in Asian skin sets out those settings and the questions worth asking before any pigment laser. Sun exposure around treatment and a recent tan matter on either pulse width.
“A pico laser breaks up pigment that is already there. It does nothing about the reason your skin made it — which is why melasma comes back and a sun spot usually does not.”
Dr Sin YongOn what the technology does and does not reach
Where does Q-switched toning still have a role?
In low-fluence 1064 nm toning across the whole face, where the aim is to nudge diffuse tone rather than to shatter a discrete spot. Laser toning in this practice is low-fluence 1064 nm Nd:YAG energy delivered in gentle, repeated passes, and the 1064 nm wavelength is only modestly absorbed by epidermal melanin, which is what makes it workable in Singapore skin. The DEKA TORO used for the T2 Frax Radiance protocol carries 532 and 1064 nm nanosecond emissions alongside its 785 nm picosecond emission, so the choice is made per mark and per visit rather than by owning one machine.
Toning on either pulse width is not run on an open-ended schedule. Frequent repeated toning of the same area has been linked to pale, mottled spots, so the response is read between visits and the plan has a stopping point. For a dark, well-defined sun spot or freckle, the picosecond emission at 532 or 785 nm is the usual tool; for diffuse unevenness and brown marks after acne, low-fluence toning is often the more conservative route.
Pico and Q-switched lasers compared for pigmentation| Feature | Pico (picosecond) | Q-switched (nanosecond) |
|---|
| Pulse width | About a trillionth of a second | About a billionth of a second; roughly a thousand times longer |
| Main mechanism | Photoacoustic: pigment shattered by a pressure effect | Photothermal with some photoacoustic effect; more heat spreads to surrounding skin |
| Wavelengths | 532, 785 and 1064 nm on the DEKA TORO | 532 and 1064 nm; the same platform carries nanosecond emissions |
| Suits | Discrete sun spots and freckles; fractional texture work; tattoo ink | Low-fluence 1064 nm toning for diffuse tone and brown acne marks |
| PIH risk | Lower heat component; still depends on fluence, interval and sun | Higher heat component; conservative settings and pacing required |
| Melasma | Conservative adjunct only; heat is a trigger | Conservative low-fluence toning only; aggressive settings declined |
Why is melasma treated with caution on either pulse width?
Because melasma is not a deposit; it is a chronic, relapsing disorder with hormonal, vascular and ultraviolet drivers that no laser touches, and it is provoked by heat. A sun spot treated well tends not to return; melasma treated aggressively tends to rebound darker, whichever pulse width was used. The melasma page explains why diagnosis comes before any device and why in-clinic work is conservative and staged inside a plan of photoprotection and topical therapy.
The pulse-width argument therefore matters least where people most want it to matter. A picosecond laser leaves less heat, which is helpful, but the honest position is that melasma is managed rather than removed, and that any laser is an adjunct. Telling melasma apart from sun spots, post-inflammatory marks, freckles and Hori's naevus is the step that protects the outcome; the guide to which brown is yours sets the four apart.
Who should wait, and what are the risks of each?
Treatment on either laser is deferred with a recent tan or sunburn, active infection or inflammation in the area, photosensitising medication, a keloid tendency and in pregnancy. Any lesion that is changing, bleeding or irregular is examined and referred for dermatological assessment first, because a pigment laser must never be fired at a mark that has not been identified.
The risks shared by both are darkening afterwards, pale spots after repeated toning, crusting and, with excessive energy, blistering or textural change. A picosecond pulse lowers the heat component; it does not remove the need for settings chosen for the skin, paced visits and strict sun protection. Dr Sin Yong identifies the pigment, chooses wavelength and pulse width for it, and performs the treatment himself; the fee follows the type and extent of pigment and the staging, set out in writing after consultation as how fees are quoted describes.
