Alexandrite laser and Nd:YAG laser: mode of action, skin types and uses
The alexandrite laser (755 nm) and the long-pulsed Nd:YAG laser (1064 nm) are solid-state lasers and are regarded as the benchmark in laser hair removal: the alexandrite for fair skin and fine hair, the Nd:YAG for dark skin and deep-seated hair. This page explains how the two crystal lasers work, how they differ from the diode laser and what spot size, pulse duration and cooling mean.
You will also find out what running costs and what service life to expect, which clinics and studios this class of device is worthwhile for and how a session proceeds. The example used is the AlexDUAL UFO from SIACSKIN, which combines alexandrite and Nd:YAG in one device for skin types I to VI, complemented by the KYROMASTER as a cooling device.
What is an alexandrite laser and how does the crystal generate light at 755 nm?
An alexandrite laser is a solid-state laser: its light is generated in an alexandrite crystal that is excited by powerful flashes of light and then emits laser light at 755 nm. The crystal is a chromium-doped chrysoberyl. Unlike in a diode laser, the light is generally produced inside the device and guided to the handpiece via an optical fibre. Typical features of this design are high pulse energies, short pulses and a large, evenly illuminated spot. The Nd:YAG laser works on the same principle with a different crystal and 1064 nm.
The AlexDUAL UFO combines both crystal lasers in one device. Its alexandrite crystal comes from a manufacturer in the USA, and the device is developed and built in Germany.
What is the difference between an alexandrite laser and a 755 nm diode laser?
Both emit light at 755 nm, but they generate it differently and deliver it in a different form. In the alexandrite laser the light is produced in a crystal that releases very high energy in short pulses, typically within a few milliseconds. A diode laser generates 755 nm with semiconductor bars in the handpiece. It is more compact and simpler to maintain, but achieves a lower peak power and therefore usually works with longer pulses or with many small pulses using the in-motion technique. For fine hairs with little melanin, the high peak power of the crystal laser is an advantage.
SIACSKIN offers both routes: the AlexDUAL UFO as an alexandrite laser with pulses from 0.3 ms and the DEWEON 4LD as a diode laser that combines 755 nm with 808, 940 and 1064 nm.
Why is the alexandrite laser considered the gold standard for hair removal on fair skin?
Melanin absorbs 755 nm particularly strongly, and the alexandrite laser delivers this wavelength with high energy in very short pulses. On fair skin the contrast between hair and skin is high: the energy ends up in the hair and the epidermis receives little of it. Short pulses also reach thinner hairs, which give off their heat again quickly. Added to this is long clinical experience, as the alexandrite laser is among the best-studied systems for fair skin types.
In the AlexDUAL UFO, the alexandrite laser works with pulses of 0.3 to 100 ms and square spots of 10 to 40 mm. For the dark skin types V to VI, the Nd:YAG laser at 1064 nm is provided in the same device.
How deep does the long-pulsed Nd:YAG laser at 1064 nm penetrate the skin?
Of all the wavelengths used in laser hair removal, light at 1064 nm penetrates the deepest, around 4 to 6 mm depending on spot size. The reason: melanin, blood and water absorb this wavelength only weakly, so the light is intercepted later than at 755 or 808 nm. In this way it also reaches deep-seated hair roots. The weak absorption comes at a price: the hair also absorbs less, which is why the Nd:YAG laser needs more energy and works best on coarse, dark hairs. A large spot increases the depth effect because less light scatters sideways.
In the AlexDUAL UFO, the Nd:YAG laser at 1064 nm is intended for the dark skin types V to VI, with square spots of 10 to 40 mm and a total power of 7500 W.
What does long-pulsed mean for an Nd:YAG laser and how does it differ from a Q-switched laser?
Long-pulsed means that the laser pulse lasts milliseconds. In a Q-switched laser it lasts nanoseconds, so the pulse is around a million times shorter. The pulse duration determines what the light does in the tissue. Millisecond pulses heat larger structures such as hair follicles in a controlled way, which is the basis of hair removal. Nanosecond pulses generate a pressure wave that shatters tiny pigment particles, which is why they are the tool for tattoos and pigment. The same wavelength of 1064 nm thus leads to completely different treatments.
At SIACSKIN, the long-pulsed Nd:YAG is found in the AlexDUAL UFO, with pulses of 0.3 to 100 ms for hair removal. The PICOLO L, by contrast, is a Q-switched Nd:YAG laser in the nanosecond range for tattoo and pigment removal.
What is the benefit of combining alexandrite and Nd:YAG in one device?
The combination covers both ends with a single device: 755 nm for fair skin and finer hairs, 1064 nm for dark skin and deep-seated, coarse hairs. An alexandrite-only laser has to turn away dark skin types, and an Nd:YAG-only laser is weak on fine hairs on fair skin. Together, this compromise no longer applies. You also need space for only one device, one induction training session and one service partner instead of two. In the borderline range, for instance with skin type IV, you can switch to the longer wavelength depending on the skin reaction.
The AlexDUAL UFO is such a dual-wave device for skin types I to VI: alexandrite at 755 nm for fair skin, Nd:YAG at 1064 nm for skin types V to VI.
What spot sizes do alexandrite and Nd:YAG lasers have and how quickly can large areas be treated?
Alexandrite and Nd:YAG lasers mostly work with spots of between 10 and 20 mm, and some devices go well beyond that. The larger the spot, the fewer pulses an area needs and the deeper the light reaches. Work is generally carried out using the stamping technique: pulse next to pulse, with little overlap. Both legs or a back are usually treated in 30 to 45 minutes with a large spot. The prerequisite is enough power for the fluence to be right over a large area as well. A square spot has a practical advantage: the spots can be placed side by side without gaps, unlike round spots, which leave untreated corners between them.
The AlexDUAL UFO offers square spots of 10 to 40 mm with a total power of 7500 W.
How is the skin cooled during alexandrite and Nd:YAG laser treatment?
Three cooling methods are common with solid-state lasers: cold air, a cryogen spray immediately before the pulse or a cooled contact window. Cold air flows over the treatment area without contact and cools before, during and after the pulse. Cryogen spray cools very precisely within milliseconds, but requires gas cartridges as a consumable. Contact cooling involves no consumables, but demands clean skin contact. Because alexandrite and Nd:YAG work with a lot of energy per pulse, cooling is a prerequisite here, especially at 1064 nm on dark skin.
The AlexDUAL UFO has built-in compressor and fourfold cooling and needs no external cooling unit. Those who want additional cooling can add the KYROMASTER: cold air down to minus 50 °C, without consumables.
What are the running costs and service life of an alexandrite laser compared with a diode laser?
A classic alexandrite or Nd:YAG laser has higher running costs than a diode laser because more parts are subject to wear. The flashlamps that excite the crystal last, depending on the design, from a few hundred thousand to a few million pulses and are then replaced. In addition there are the optical fibre and the protective window on the handpiece, cooling water and filters and, in devices with cryogen spray, the gas as well. The crystal itself hardly ages. In a diode laser, by contrast, the handpiece with the laser bars is the wear part. Before buying, ask which parts fall due after how many shots and what they cost.
In the AlexDUAL UFO, the crystal is designed for up to 100 million shots, and the device does without an external cooling unit.
Which clinics and studios is an alexandrite and Nd:YAG laser worthwhile for?
This class of device is worthwhile for businesses in which hair removal is a main focus and the utilisation supports the higher investment: dermatology practices, aesthetic clinics and specialised laser studios with several treatment rooms. Typical reasons are demanding clients with fine residual hairs after earlier treatments, an international clientele with all skin types and the wish to stand out from studios with a diode laser. For getting started on a smaller budget, a diode laser such as the DEWEON 4LD is usually the more economical choice.
The AlexDUAL UFO is built for this level of demand: alexandrite and Nd:YAG in one device, skin types I to VI and the SIA AI with cameras on the handpiece.
What is the long-pulsed Nd:YAG laser used for apart from hair removal?
Long-pulsed Nd:YAG lasers are generally also used for vessels such as thread veins and for non-ablative skin rejuvenation. This is made possible by the great penetration depth of 1064 nm: the light reaches deeper-lying vessels and heats the dermis, which stimulates collagen formation. Which of these applications a particular device covers depends on the pulse duration, spot, cooling and the manufacturer's intended purpose.
The AlexDUAL UFO is designed for hair removal on the face and body. For vessels and redness, SIACSKIN has other devices: the Velaslift, a diode laser with four wavelengths for vascular lesions and thread veins, and the DERMAFORCE BBL PRO, a BroadBand Light system for redness and couperose.
Which laser targets fine residual hairs when the hair becomes thinner after a few sessions?
For fine residual hairs that still contain pigment, the alexandrite laser at 755 nm with short pulses is the obvious choice. Over a course of treatment, the remaining hairs become thinner and lighter. They contain less melanin and give off heat faster, so that long pulses and longer wavelengths hardly heat them sufficiently any more. The 755 nm wavelength is absorbed by melanin considerably more strongly than 808 or 1064 nm, and pulses of a few milliseconds heat even a thin hair before the heat dissipates. Limits remain: white, grey and red hairs hardly respond to lasers.
The AlexDUAL UFO works with alexandrite at 755 nm and pulses from 0.3 ms. For light, blonde and very fine hairs, SIACSKIN has the VCL DERMALIGHT, an LED system with 750 to 890 nm.
How do you treat a mixed clientele with skin types I to VI using one device?
With two wavelengths in one device and a fixed routine: determine the skin type, select the wavelength, deliver a test pulse, wait for the reaction. For fair skin you use 755 nm, for dark skin 1064 nm with a longer pulse and strong cooling. The most common source of error here is a fresh tan, which makes the skin 1 to 2 levels darker than at the last appointment. So document the settings and reaction for every area, so that a colleague can also continue safely at the next appointment.
With alexandrite and Nd:YAG, the AlexDUAL UFO covers skin types I to VI. Using cameras on the handpiece, the SIA AI sets skin type, body area and energy automatically, and the client management system documents the treated areas.
What happens during a session with an alexandrite or Nd:YAG laser?
A session begins with a look at the skin and hair and a test pulse, after which the treatment area is worked through pulse by pulse. The skin is freshly shaved and clean, and everyone in the room wears protective eyewear matched to the wavelength. The pulses are placed side by side, with slight overlap and continuous cooling. Underarms take a few minutes, both legs usually 30 to 60 minutes. Immediately afterwards, redness and small swellings around the follicles are normal and usually subside within hours. The usual course is 6 to 8 sessions at intervals of 4 to 8 weeks.
With the AlexDUAL UFO, the SIA AI sets skin type, body area and energy automatically. The square spots of 10 to 40 mm can be adapted to small and large areas alike.
Is treatment with an Nd:YAG laser more uncomfortable than with an alexandrite laser?
Yes, most people find the Nd:YAG laser somewhat more intense than the alexandrite laser. The reason lies in the physics: 1064 nm is absorbed more weakly by the hair, so more energy is used, and the heat is generated deeper in the tissue. It is described as a short, deep pulse of heat, whereas the alexandrite laser feels more like a quick flick on the surface of the skin. How strong the sensation is depends on the area, hair density and cooling. With every session there are fewer hairs, and the treatment becomes more comfortable.
The AlexDUAL UFO cools with compressor and fourfold cooling. For sensitive areas the KYROMASTER can be added, which cools with cold air down to minus 50 °C before, during and after the pulse.
