Pigment absorbs laser light and heats up. That is true of tattoo ink and of the melanin in a sun spot. An older laser delivers that energy over nanoseconds (billionths of a second), and some of the heat spreads into the surrounding skin before the pulse ends.
A picosecond laser does the same job in a few hundred picoseconds (trillionths of a second). The particle has no time to shed heat, so rather than being cooked it is hit by a sudden pressure wave that cracks it apart. People who work with lasers call this a photoacoustic effect rather than a photothermal one — shock rather than burn.
Smaller fragments matter for two reasons. Your immune cells carry ink away a fragment at a time, so finer debris clears faster and in fewer visits. And because less heat leaks sideways, there is less of the inflammation that sets off post-inflammatory hyperpigmentation, the brown stain that can follow any injury to pigmented skin.
Most pico platforms also have a lens or diffractive array that concentrates the beam into a grid of high-energy dots below the surface. Those dots create tiny controlled injuries in the dermis without breaking the skin, which prompts collagen repair. That is the setting used for acne scarring, pores and fine lines, and it works by a completely different route from the pigment setting.
Ask which device, which wavelength, and who will be holding the handpiece. On pigment work the settings and the operator's judgment matter more than the brand name on the machine.
Ask for a test spot if you have brown or Black skin, or if you have melasma. A small test in a hidden area, looked at two to four weeks later, tells you more than any consultation.
Photograph your tattoo or your spots yourself, in the same light and from the same angle, before the first session. Fading is gradual and memory is unreliable.
No sun on the area and no self-tanner. Tanned skin absorbs the laser and burns.
Stop retinoids and exfoliating acids on the area a few days beforehand.
If you get cold sores and the treatment is near your mouth, ask for antiviral tablets to start the day before.
Come with clean skin. No makeup, moisturizer or sunscreen on the area.
Numbing cream is standard for tattoos and optional for a few spots. It needs 30 to 60 minutes to work, so arrive early if the clinic applies it there.
Wear something you do not mind getting ointment on afterwards.
You put on protective eyewear. So does everyone else in the room, including the person treating you.
The provider usually fires a few test pulses at the edge of the area to check how your skin reacts before treating the whole thing.
Each pulse feels like a rubber band snap or a spatter of hot grease. Tattoos hurt more than sun spots. Bony areas — ankle, ribs, collarbone — hurt more than fleshy ones.
Treated pigment often turns white within a second or two. That frosting is trapped gas from the shattered particles and it fades within about 20 minutes. It is expected, not a burn.
A few sun spots take under five minutes. A palm-sized tattoo runs 10 to 20 minutes. Large back pieces are often split across visits.
Afterwards the skin is red, warm and puffy, a bit like sunburn. Tattoo areas may be raised and welted.
Cold air or an ice pack is used during and after to keep you comfortable, and ointment plus a dressing goes on tattoo work before you leave.
Practical rules throughout: keep the area moisturized, wash gently, no swimming pools, hot tubs, saunas or heavy sweating until scabs are gone, and daily sunscreen on any exposed treated skin for at least a month. A tinted sunscreen with iron oxides is better than a clear one if pigment is the reason you were treated.
There is no home version of a picosecond laser and there will not be one. These are class IV medical lasers costing well into six figures, and the whole point of the technology is a peak power that would be unsafe in untrained hands.
Devices sold online as home "pico" or "blue light picosecond" pens for tattoo and spot removal are not picosecond lasers. They are low-power devices that at best do nothing and at worst burn you. Tattoo removal creams do not work on ink sitting in the dermis, because nothing you spread on the surface reaches it.
For flat brown spots, the genuine at-home route is a pigment routine rather than a device: daily sunscreen, a retinoid, and an evidence-backed lightener such as azelaic acid, tranexamic acid or alpha arbutin. Slower than a laser, much cheaper, and it addresses new pigment as well as old.