Hair removal laser technology: Liquid fiber optic laser diode

Liquid fiber-optic delivery of high-peak-power laser diode has now become a reality. Monocrom calls it THEA technology — an intelligent combination of re-shaping and integrating optics, along with the use of a liquid optical fiber.

Monocrom’s fiber-coupled high-power laser diodes employ a liquid fiber bundle measuring 3 to 5 mm in diameter. They are perfect for hair removal treatment.

Fiber coupling is the main reason for making the handpiece of this diode-based hair removal system easier and lighter, and thus more ergonomic. Monocrom has kept the large laser components inside the main body of the equipment, whereas the handpiece features only the fiber end in addition to sensors, a simple lens set and minor electronic components.

Indicated for

  • Hair removal

A liquid fiber has been selected purposely as it is less sensitive to extreme bending radii and is not likely to break down since fluid is present inside. Liquid fiber is also more efficient in light transmission compared to conventional solid fiber bundles.

Monocrom’s liquid fiber laser diodes integrate various wavelengths in the same laser system, allowing a single HPDL source to cover the entire range from 760 to 1064 nm.

Benefits

  • Lightweight, ergonomic and shock-resistant handpiece
  • Flat ­top beam profile
  • Non-soldered laser bars — CLAMPING® Tech inside
  • Visible aiming beam
  • Efficient cooling system
  • The diode has a prolonged, useful lifetime

Technical parameters

Source: Monocrom

Technical specifications Parameters
Peak wavelength [nm] 760/808/1064 nm single or combined
Peak power up to 2500 W
Pulse width up to 500 ms
Optical Transmission Efficiency up to 90%
Spot size 1.5 - 2.0 cm2
Aiming beam (included as standard) 520 nm

 

LIV curve for 10 laser bars, 3K W, 808 nm THEA module. Higher peak powers can be achieved for a 20 laser bar, 5 kW, 808 nm + 880 nm THEA module.

LIV curve for 10 laser bars, 3K W, 808 nm THEA module. Higher peak powers can be achieved for a 20 laser bar, 5 kW, 808 nm + 880 nm THEA module. Image Credit: Monocrom

Energy per pulse for 3 different operating modes (10 Hz 5 ms, 10 Hz 10 ms, and 3 Hz 30 ms).

Energy per pulse for 3 different operating modes (10 Hz 5 ms, 10 Hz 10 ms, and 3 Hz 30 ms). Image Credit: Monocrom

Flat top profile, easy handling and much more

  • Fiber optic delivery for convenient handling
  • The visible aiming beam displays the precise area treated by the laser
  • Flat-top beam profile with almost no divergence, assuring uniform energy distribution and improved penetration to achieve a more efficient depilation effect
  • The handpiece exit window does not make contact with the skin and thus prevents the migration of gel and hairs into the optics
  • Since the diodes are integrated into the machine, high-current cables are located far from the operator’s hand

Since the high-power diode laser is remoted within the machine, a variety of handpieces can be exchanged easily by simply detaching the fiber to achieve various spot shapes or sizes on the skin.

Hair removal laser technology: Liquid fiber optic laser diode

Image Credit: Monocrom

Overview

Removing unnecessary body hair is a very common and prevailing practice throughout the world, and this has quickly grown over the past few years to address both men’s and women’s requirements. Since the late 1990s, light-assisted hair removal (LHR) methods have shown unparalleled effectiveness when compared to conventional techniques, enabling an almost permanent hair loss.

A growing demand followed by an active market competition has fueled a constant quest for cost reduction and technology advancement. As a result, this has now become an affordable and highly accessible treatment, even in the form of small devices for domestic use.

Light-assisted hair removal principle

The fundamental principle of light-assisted hair removal is that a suitable light source can damage the stem cells surrounding the hair follicle, causing minimum or no damage to the skin or neighboring tissues. Therefore, new hair is prevented from growing for extended periods of time, months, years, or even permanently.1

A “suitable light source” should be understood as the right combination of fluence, wavelength and pulse duration. With respect to wavelength, the range 600 –1100 nm is favored because melanin contained in hair (and certainly skin) absorbs light inside this range.2 Moreover, if the wavelength is longer, the penetration will also be deeper into the skin tissue.

Relative absorption (logarithmic scale) of light by skin chromatophores (top). Depth of penetration of light radiation according to its wavelength (bottom).

Relative absorption (logarithmic scale) of light by skin chromatophores (top). Depth of penetration of light radiation according to its wavelength (bottom).

Figure 1. Relative absorption (logarithmic scale) of light by skin chromatophores (top). Depth of penetration of light radiation according to its wavelength (bottom). Image Credit: Monocrom

At specific fluence levels (in the range of 10 to 100J/cm2), the absorbed light is converted into heat that actually burns the hair. Pulse duration (normally ranging between 10 and 100 ms, but larger and shorter can be selected) should be set to obtain a threshold temperature at the hair follicle, and keep it long enough to impair the stem cells.

This threshold temperature, however, should not be too long to expand the volume of the affected skin as this would cause unwanted damage to tissues and discomfort to the patient.

Another aspect to remember is the relative melanin concentration in the hair and skin, which relates to the phototype of the skin (Fitzpatrick scale).

Skin phototype classification according to the Fitzpatrick scale.

Figure 2. Skin phototype classification according to the Fitzpatrick scale. Image Credit: Monocrom

Darker skin is caused by a higher concentration of melanin, and the same principle applies to different kinds of hair. Therefore, the effectiveness of light-assisted hair removal is optimized on white-to-moderate brown skins and with dark hair (phototypes II to IV).

Phototypes I and VI are extreme cases and are more crucial, but LHR can still be viably effective if the right fluence, wavelength and pulse duration are selected.1

Types of light sources

Fundamentally, there are two types of light sources that can produce light pulses that are intense enough for light-assisted hair removal. One type is called the intense pulsed light (IPL), which depends on Xenon flash lamps, and the other one is the laser.

Two main typologies are utilized in the laser option. These include high-power diode lasers (HPDLs) and solid-state lasers (SSLs). The ideal light source does not exist, and because of this reason, all the mentioned types are extensively used today.

The major benefit of IPL is its lower technical complexity, which makes it the most affordable option. However, it also has the lowest effectiveness. IPL heads produce radiation in a broad spectrum (600–1200 nm),1 which implies that other kinds of molecules, excluding melanin, have the ability to absorb light (Oxyhemoglobine and water).

Different types of light sources show different emission wavelengths.

Figure 3. Different types of light sources show different emission wavelengths. Image Credit: Monocrom

This would cause additional heating of the irradiated area and thus lead to more pain. Moreover, IPL applicability is restricted to phototypes I and II.1

When considering solid-state lasers, the Alexandrite laser was the first to be widely used for light-assisted hair removal. It has the bulkiest and complex architecture among the cited light sources, hence the higher cost. However, the effectiveness of this laser is still the best for phototypes I and II.

While the Alexandrite laser produces laser light at 755 nm, the Nd:YAG lasers emit at 1064 nm, so they are suitable for darker skins (phototypes V and VI).

In between these two lasers, high-power diode lasers are the best trade-off in terms of versatility (relevant mostly to phototypes II to IV), cost and effectiveness. Conventionally, the emitting wavelength of these lasers is in the range of 800–810 nm for light-assisted hair removal applications.

Now, however, it is possible to manufacture commercial HPDLs systems that emit in the range of 760 to 1064 nm and beyond. Therefore, high-power diode laser technology could be used on any skin phototype and can substitute any other prevailing LHR system.

High-power diode lasers on its race to hegemony in LHR

Why are Alexandrite lasers and Nd:YAG lasers still being used? This is because solid-state lasers serve as brighter light sources when compared to high-power diode lasers. This means that light beams coming out of solid-state lasers can be focused on smaller spots — in contrast to high-power diode lasers that turn into higher power density — and the possibility to be fiber-coupled.

The handpiece of laser hair removal systems, based on solid-state lasers, is lighter, simpler and more ergonomic, and this is mainly down to fiber coupling. The bulky laser components are maintained within the main equipment body.

The handpiece contains only the fiber end, in addition to sensors, a simple lens set and minor electronic components. While other features can be added, such as liquid-cooled tips for high fluence values, they tend to make the handpiece bulkier.

The light source, by contrast, is located in the handpiece itself in the high-power diode laser (and IPL) systems. This includes the diode laser stacks (which are chiefly copper), the cooling pipes for the stacks and the tip (if it is the case) and the wiring (which is again copper), which often shows a large cross-section in the range of 3 to 6 mm.

Additionally, the front of the laser stacks may contain more or less bulky optics, such as homogenizing rods or prisms. These collectively result in a handpiece that is heavier than 500 g, along with the water and power supply cable. This does not actually contribute to the ergonomics or comfort from the operator’s point of view.

Can high-power diode lasers be fiber-coupled in almost the same way as solid-state laser systems, retaining all the bulky components in the main equipment body, leaving behind just a compact and ergonomic handpiece? What if different wavelengths were integrated into the same laser systems, so that the entire range from 760 to 1064 nm could be covered by just a single HPDL source?

These approaches are now possible at Monocrom, thanks to Thea technology — a smart combination of re-shaping and combining optics along with the use of a liquid optical fiber.

Hair removal laser technology: Liquid fiber optic laser diode

Image Credit: Monocrom

The new kinds of fibers help transmit light from laser sources that are not as bright as solid-state lasers because of their high angle of acceptance (NA < 0.3) and larger diameter (Ø 3 to 5 mm).

Yet, ultimately, analogous laser spot sizes and fluence values will be used on the patient’s skin, with even more distribution of flat-top intensity.

The liquid fibers are less vulnerable to excessive bending radii and are not likely to break down because of the presence of liquid. When compared to conventional solid fiber bundles (packing factor is 1), liquid fibers are also more efficient in transmitting light.

The unique clamping technology from Monocrom allows the best diode performance, leading to higher peak power values and higher lifetimes (108 shots).

Intensity distribution of the laser spot homogenized through the liquid fiber.

Figure 4. Intensity distribution of the laser spot homogenized through the liquid fiber. Image Credit: Monocrom

To sum up, high-power diode laser systems are gaining traction in the light-assisted hair removal application compared to that of their solid-state laser competitors due to the deployment of novel solutions offered by Monocrom.

Reference

  1. Stephanie D. Gan and Emmy M. Graber, Laser Hair Removal: A Review, Dermatologic Surgery 39 (6), 823-838 (2013)
  2. Stratigos A.J. and Dover J. S., Overview of lasers and their properties, Dermatologic Therapy 13 (1), 2-16 (2000)