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Optical elements for aesthetic laser applications


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any dermatological and skin care procedures such as hair and tattoo removal,


acne and scar reduction, and skin revitalisation are reliant on lasers for their respective treatments, where structures within the skin are modified using the photo- thermal and photo-acoustic effects produced by laser light energy. Many aesthetic lasers used for


dermatological treatments employ intra-cavity or extra-cavity optics or optical assemblies. Here, we examine a few cases where optical elements are utilised within these systems to couple, shape, or direct laser light for application to patients’ skin.


Optics in skin rejuvenation Skin rejuvenation procedures often come in the form of ablative (skin tissue is vaporized) and non- ablative (skin remains intact) laser treatments. Some non-ablative laser treatment methods utilize non- uniform, fractionated beam delivery. Whilst non-fractionated lasers act on the entire projected surface area of the skin, fractionated lasers target multiple, equally distributed portions of the projected area. Fractionated beams consist


of several high-intensity zones surrounded by lower-intensity zones. The higher-intensity zones heat select portions of the target tissue to temperatures sufficient for a first treatment (e.g. collagen shrinkage), while the lower- intensity zones provide sufficient energy to the surrounding tissue for a second treatment. This process stimulates collagen regeneration to ‘fill in’ wrinkles and make skin look younger. Fractionated laser beams are


achieved by coupling the output beam from a laser source with an optical system that modifies the beam profile to a large-diameter beam with a non-uniform energy profile. Differing configurations of fibre bundles, axicon lenses, and diffractive or refractive lens arrays may be leveraged to provide non-uniform energy output beams. Figure 1 demonstrates how a


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diffractive element and lens could be combined to create an array of focal points.


Optics in tattoo removal Tattoos are permanent designs made of pigment that is injected into the skin’s dermis. The dense layer of pigment/ink that is created is too much for the body’s immune system to remove, and so it becomes entrenched below the dermis-epidermis interface. To remove tattoos, pulsed laser light is used to break down the larger ink particles into ones small enough to be engulfed by the immune systems’ phagocytes which then naturally remove these from the body as waste. Laser tattoo removal procedures commonly employ solid-state lasers, e.g. Alexandrite, pumped by a second solid-state laser, e.g. Nd:YAG, with a q-switch and frequency converting elements, an example of which can be seen in Figure 2. In this case, the first laser cavity includes a highly reflective mirror and output coupler mirror. This output coupler is a partially reflective mirror, either flat or curved, which allows part of the circulating intracavity power to be released from the first laser cavity. The second laser cavity, in this case, would include a high reflecting pump mirror and an output coupler mirror since the second 1064nm solid-state laser is pumped by a portion of the initial 755nm output beam. Aesthetic laser systems such


as these vary by gain material, pulse intensity, and pulse duration depending on the application and precision needed for a given treatment. For example, due to the different optical absorption of the various colours of tattoo pigment, an Alexandrite laser can remove blue, purple, and green tattoos, while an Nd:YAG laser can remove black tattoos.


Laser light beam delivery Typical primary or pump laser dermatology units consist of a main body inside of which the


Figure 1: Conceptual generation of spots from a diffractive beamsplitter and lens


Figure 2: Typical layout of a solid-state laser pumped by a second solid-state laser with a q-switch and frequency converting elements, commonly used for tattoo removal


Figure 3: A schematic drawing of a handpiece including a solid-state laser pumped via an optical fibre by another solid-state laser.


primary or pump laser is stored, an articulated mirror arm or optical fibre, and a handpiece at the end, usually with an optical assembly inside, which shapes the laser beam and directs it to the patient’s skin. Sometimes, these handpieces also include a second laser gain material which is pumped by the primary unit. Coupling the output laser beam


of the primary laser into the gain material of a second laser can be accomplished in a variety of ways. Figure 2 shows a direct approach. However, depending on pulse intensity, pulse duration, and wavelength, an optical fibre may be used to transmit the beam to a hand-held device.


Figure 3 shows a schematic


drawing of a handpiece including a solid-state laser pumped via an optical fibre by another solid-state laser. The beam exiting the optical fibre is collimated by several lenses before being directed into the gain material. The output beam of the handpiece can further be optically modified by a beam shaper before it is used to treat the skin of a patient.


Edmund Optics proudly


manufactures laser optics used in skin care.


Inquiries about complete


systems should be directed to the skin care device manufacturers. EO www.edmundoptics.co.uk


July 2021 Electro Optics 17


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