LASER

Light Amplification by Stimulated Emission of Radiation

Ashwin kumar sanapalaMIMS

Quantum physics

Stimulated emission

• Is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron, causing it to drop to a lower energy level. The liberated energy transfers to the electromagnetic field, creating a new photon with identical phase, frequency, polarization, and direction of travel as the photons of the incident wave.

• This is in contrast to spontaneous emission which occurs at random intervals without regard to the ambient electromagnetic field.

• A laser is a device that generates an intense beam of light.

• The wavelength : is defined as the distance between the crests of each wave and that determines the functional properties of the laser energy..

• Wavelengths in the 0.4-0.7um range form the visible light of the spectrum.

• Ultraviolet rays, X-rays and gamma are forms of electromagnetic radiation with the wavelengths shorter than the visible light.

• Surgical lasers fall between the longest and the shortest wavelengths, in the infrared and visible as well as the ultraviolet portions of the electromagnetic spectrum.

• The type of laser depends on the active medium used.

• The most commonly used medical lasers are, the carbon dioxide, ruby, argon, krypton, YAG and Excimer.

LASER - skeleton

The components of laser system:

Power source: • pumps energy into the lazing medium. • The power pumping energy is related to the

composition of the medium in the laser.• The power source in lasers may be electrical

as in Argon and carbon dioxide or flash lamps as in pulsed dye laser.

Lasing cavity: • which is a tube with mirrors placed at each end

where amplification of stimulated emissions of radiation occurs.

• Photons traveling the length of the tube are reflected back through the medium.

• Each time the beam reflects back and forth or resonates through the axis of the medium, more atoms are stimulated to release photons, and the laser effect is amplified.

• The end of the mirrors has a small opening allowing a minute part of the laser light to be transmitted.

A wave guide: • The laser light is invisible and therefore a

fibro- optic HeNe low beam is used to guide the laser light towards the desired tissue to be treated.

PROPERTIES OF LASER LIGHT

Laser light has three special qualities that distinguish, it from the conventional light source .

• Collimated: means that laser light travels parallel in a single direction with very little divergence even for a long distance and therefore there is minimal loss of power along the beam . A laser beam is a 1000 times brighter than the daylight and is brighter than the sunlight.

• Monochromatic: consists of one color or wavelength and thus the laser beam is very pure. In contrast, white light from a regular light bulb involves the spontaneous emission of photons of many wavelengths or colors, traveling in various directions and emitting diffuse light.

• Coherent: means all of the light waves move parallel in phase together in both time and space. Ordinary light from a lamp consists of a mixture of wavelengths radiating in different directions and out of phase . It is in a laser term considered as incoherent.

MODES OF ACTION OF LASER LIGHT• This depends mainly on the absorption of a photon by a

chromophore or the target tissue such as melanin pigment, water or hemoglobin.

• The photon surrenders its energy to the chromophore and then ceases to exist where the energy is converted into heat, which is dissipated to the neighboring tissue, by conduction or radiation.

• In the cells most proteins , DNA, RNA, membranes and their integral structures start to melt at temperature more than 40 degree centigrade where tissue becomes coagulated .

• The severity of coagulation or tissue denaturation depends on both the fluence and time of exposure.

LASER TERMS

• Ablation: removal of tissue by vaporization.• Beam: a ray of light.• Divergence: increase in beam diameter with distance

from the exit aperture of laser.• Chromophore: optically active material in tissues that

can act as an absorptive target for laser (melanin, hemoglobin water).

• Absorb: To take up matters or energy.• Absorption coefficient: Ability of light to be absorbed.• Active medium: The active material in the laser.

• Intensity: the power transmitted by a light wave across a unit area perpendicular to the wave.

• Power: the time rate of doing work (watt)• Power density: the power of the laser beam

per unit area (watts/cm2).• Excitation: The addition of energy to a particle

or system.

• Fiberoptics: a system of flexible quartz or glass fibers with internal reflective surfaces that pass light through thousands of glancing reflexes.

• Aiming beam: HeNe of low density beam used to guide the invisible laser light to the treatment area.

• Laser medium: (active medium) material used to emit the laser light.

• Coagulation: destruction of tissues by heat without physically removing it.

• Collimation: all rays coming from laser are parallel to each other.

• Coherent radiation: same wavelengths move together to different points.

• Thermal relaxation time: The time it takes heat to diffuse out of a structure and into surrounding structures by thermal conduction.

When pulsed, duration of a laser is shorter than the time required for heat to spread out of a target, the heat damage will be confined to the target.

• Target site: tissue that is aimed or fired with the laser beam.

• Photocoagulation: tissue coagulation by laser light.

• Mode : the way in which laser beam is distributed.

TYPES OF LASERS USED IN DERMATOLOGY

Lasers can be categorized into three types:1. Lasers that emit visible light: - These lasers, which emit visible light ranging from

the blue to the red portions of the electromagnetic spectrum, are used in treating vascular and benign pigmentary conditions.

- They include argon, argon pumped tunable dye, flash lamp pumped pulsed dye, copper vapor, copper bromide and krypton lasers.

- The blue,green, red and yellow emission wavelengths are characteristically absorbed by the two main natural chromophores of the skin, hemoglobin and melanin.

2. Lasers that emit infrared light: - These include the carbon dioxide and neodymium:yttrium–

aluminium–garnet( Nd:YAG) laser.- Both these emit energy in the infrared portion of the

electromagnetic spectrum so there is no preferential absorption of the laser light energy by melanin or hemoglobin.

- The carbon dioxide laser, in the far infrared portion, is selectively absorbed by water and the effect of this laser on tissue is determined by the water content.

- The invisible, near-infrared wavelength of light from the Nd:YAG laser is not specifically absorbed by any component of the skin or internal organs resulting in a diffuse nonspecific thermal effect. Since its energy is absorbed by volume, it has been used mainly as a coagulator.

3. Lasers that emit very short pulse (nano-seconds) of visible or infrared light:

- These are Q-switched lasers that produce short, high intensity nano-second bursts.

- The movement of the wave through the tissue produces kinetic energy which can fracture or disintegrate tattoo pigments or melanin.

- These lasers are used for the treatment of benign pigmented lesions and the removal of tattoos.

Indications

Treatment of Benign Cutaneous Lesions

1. Carbon dioxide laser:• The CO2 laser emits far infrared radiation at 10,600 nm. • The chromophore of absorption is water.• The laser energy is superficially absorbed by tissue water,

which limits penetration of the laser to a depth of 0.1 to 0.2 mm with minimal scatter.

• Continuous-wave CO2 laser can produce a more limited area of tissue damage (peripheral damage limited to 50 to 100 mm).

• treatment of choice are refractory warts, rhinophyma, epidermal nevi, seborrheic keratosis, angiofibromatous and angiolymphoid lesions, and benign superficial dermal tumors.

2. Pulsed dye laser at 585 mm:• The PDL is pulsed at 450ms with a

wavelength of 585 nm, which makes hemoglobin the primary target chromophore.

• This high energy and short pulse duration impart the capacity to destroy target blood vessels with high specificity and with minimal damage to the epidermis and surrounding structures, which results in a very low incidence of scarring.

• It is used for benign lesions with a vascular component like verruca vulgaris, verruca plana, keloids, angiofibromas, and rosacea.

3. Argon laser: • The argon laser, with wavelengths of 488 and

514.5 nm, targets hemoglobin and melanin.• It is used for benign lesions with a vascular or

pigmented componen like telangiectasia, seborrheic keratosis, rosacea, angiofibromas and pyogenic granulomas.

4. Neodymium: Yttrium–Aluminium–Garnet laser:• The Nd:YAG laser has a wavelength of 1064 nm,

which is absorbed by proteins of any opaque tissue, darker tissue showing preferential absorption.

• Its frequency can be doubled to a 532 nm wavelength.

• Treatment of keloids and early lesions of seborrheic keratosis.

5. Pulsed dye pigmented laser: The pulse dye-pigmented laser, at a wavelength of

510 nm, has been used to treat flat seborrheic keratoses.

6. Q-switched ruby laser: The Q-switched ruby laser, with a wavelength of

694 nm, has been reported to achieve 75% resolution of seborrheic keratoses.

Treatment of Vascular LesionsA variety of lasers is available for vascular lesions and

telangiectasias.• Continuous Wave (CW) units utilize wavelengths from 488

to 578 nm. • The target chromophore is oxyhemoglobin, although some

melanin absorption also occurs, principally at shorter wavelengths.

• Penetration is approximately 1 mm and is greatest at longer wavelengths.

• Facial telangiectasia is the most common indication of CW laser.

• The pulsed dye laser (the flashlamp-pumped pulsed dye laser; FLPDL) was developed specifically for vascular lesions especially port-wine stain.

• In addition to telangiectasias, capillary hemangiomas, venous lakes, small cherry angiomas also respond to treatment.

• The double Nd:YAG laser (532 nm) is effective for treating telangiectasias.

• The alexandrite 755 nm and Nd:YAG (1064nm) lasers have been used to treat bulky malformations and port-wine stain.

• The intense pulse light (IPL) laser has a noncoherent broadband light source with wavelengths in the range of 515–1200 nm and various pulse widths.

• Filters are used to block unwanted wavelengths.• It has been used to treat port-wine stain,

hemangioma, and telangiectasias.

Treatment of Pigmented Lesions1. Continuous wave lasers: • These are argon (488 and 514nm), green light KTP (532 nm)

and carbon dioxide (10,600nm) lasers.• used to treat epidermal but not dermal lesions through

nonspecific thermal damage.

2. Q-switched ruby laser:• The laser beam produced is red light of wavelength 694 nm.• Q-switching results in pulsed emission of coherent light.• It is used in the treatment of lentigo, café-au-lait patches,

melasma, nevus of Ota, and infraorbital skin darkening.

3. Nd:YAG laser:• Its high power pulses and short exposure time allows precise

treatment of target tissue with minimal thermal damage.• It is used in the treatment of tattoos, caféau lait macules, Becker’s

nevus, and post-inflammatory pigmentation.

4. 510 nm Pulsed dye laser:• It is used for removal for pigmented lesions confined to the

epidermis. • Used for treatment of cafe-au-lait patches, Becker’s nevus,

postinflammatory pigmentation, nevus of Ota, nevus of Ito, and melasma.

5. Alexandrite laser: • The alexandrite laser 760 nm penetrates into the dermis and is used

to treat dermal pigmented lesions.

Lasers for Hair Removal• The chromophore for selective targeting of hair follicles can

be endogenous or exogenous:

1. Endogenous chromophore (Melanin): • Melanin in the hair shaft of the follicle provides a

chromophore that is not present in the surrounding dermis and that allows selective targeting of hair in the skin.

• Thus, at deeply penetrating wavelengths in the 600 nm to 1100 nm region, melanin absorption may be used for selective photothermolysis of hair follicles.

Lasers that target melanin are:a. Diode laser: • The diode laser emits a

wavelength of 800 nm and also causes hair removal by effectively targeting melanin while deeply penetrating the dermis.

• This may allow safer treatment in dark skinned individuals.

b. 694-nm Ruby lasers: • Because of high melanin

absorption at 694 nm, ruby lasers are indicated in lightskinned (Fitzpatrick skin types I to III) individuals.

c. 755-nm Alexandrite lasers:

• Several long-pulsed alexandrite lasers have been introduced recently for hair removal.

• The longer wavelength allows a slightly greater depth of penetration, and there is a lower risk of epidermal damage because of slightly less melanin absorption at this wavelength.

2 . Exogenous chromophore:• Rather than targeting endogenous melanin, an

exogenous chromophore (e.g. dyes, photosensitizers, and carbon particles) can be introduced into the hair follicle and then irradiated with light of a wavelength that matches its absorption peak.

• The technique is inadequate for inducing permanent hair loss because penetration of the chromophore into all depths of the hair follicle is not reliable

The Q-switched Nd:YAG laser targets exogenous chromophores.• It produces light at 1064 nm in the near infrared spectrum.• Water, hemoglobin and melanin are poorly absorbed at this

wavelength.• Hence, the laser is employed in combination with a topical

pigmented carbon-based suspension as an exogenous chromophore.

• This method provides a selective target that is independent of the color of the hair shaft.

• This permits effective treatment of even light-haired individuals who lack significant hair melanin, the main chromophore for other laser systems.

Intense Pulsed Light Systems

• Pulsed, noncoherent broadband light sources are now widely used for hair removal and other applications. Intense pulsed light (IPL) systems utilize a xenon bulb as a light source, which produces polychromatic light with wavelengths from 550–1200 nm.

• This is in contrast to laser light sources, which produce monochromatic light of a specific wavelength. Light emitted by the bulb passes through a filter that excludes shorter wavelengths that may severely damage the skin.

• The ability to “tune” the wavelength of light emitted by these systems gives IPL systems the advantage of versatility. Using different filters, a pulsed light system could mimic any number of laser systems, allowing the operator to treat many different conditions amenable to light therapy, including, of course, the removal of unwanted hair.

• Studies have shown intense pulsed light to be an effective method of hair removal.

• The variability of light output can also be a disadvantage of IPL systems.

• The light spectrum may vary slightly with each pulse, and reproducibility of treatments varies between operators.

• The hand pieces of IPL systems are typically larger than laser-based systems, which makes treatment of fine areas of the skin difficult.

Laser Resurfacing of the Face1. Carbon dioxide laser:• The carbon dioxide laser available in CW or pulse

mode is used for both excisional and ablative surgeries.

• The excisional mode is used for keloid removal, scalp reduction, debulking rhinophyma, and removal of malignancies.

• The ablative/vaporizing mode has become popular for treating rhytides, photoaging, acne scars, adenoma sebaceum, and multiple trichoepitheliomas, through resurfacing techniques as the cosmetic results are excellent.

2. Erbium:YAG laser: It is used for resurfacing wrinkles and scars.

3. Combined CO2/Er:YAG laser: Both the laser energies are

• combined simultaneously in a synchronized manner. • The combined system gives the benefit of precise

ablation, short recovery, minimal side effect, collagen tightening, an ability to treat deep wrinkles

LASER SAFETY

1) The operating room• Instruments used should be of special type

not reflecting laser light.• The room should not contain volatile

substances such as ether, alcohol .• Gauze used should be moistened with water

to prevent inflammation by the laser light.

2) Safety measures for the patient:• Special glasses should be used.• different lasers have different glasses.• Eye shields: applied and cover the eyes by moist

gauze before applying the glasses.• Patient's lips can be protected by moist gauze. When

operating in the oral cavity, care should be taken to protect teeth and bone by using wet gauze or other nonflammable, heat absorbing protective material.

• Char can be removed by moist saline gauze , where charred areas may reach very high temperature as laser energy continues to be applied causing more destruction to tissues.

General measures• The surgeon and the assistants should use the special

glasses for the particular laser.• NEVER look directly into the laser source or at sites of

laser reflection.• Both direct and reflected laser output can contain

enough energy to cause permanent eye injury.• NEVER allow anyone near the laser while it is in use

without protective eyewear.• NEVER point the hand probe in any direction, except

toward the area to be treated.• Before activating a hand piece, confirm that the tip of the

probe is pointed in safe direction..

• If the HeNe beam (which is weak laser beam used to guide the direction of the intense laser beam emitted from the machine for surgical application) is absent, first make sure first that the" Manual Safety Shutter" is in the open position.

• NEVER place hands or other objects in the path of the carbon dioxide beam. Severe burn may occur.

• NEVER discharge the laser without a target to absorb it and without consideration giving to what lies behind the target. Saline soaked gauze sponges or saline moist gauze or water soaked clean gauze can be used to protect tissues

• LASER FOOT SWITCH :only the surgeon should have access to the laser Footswitch.

• NEVER press the foot paddles unless you are starting treatment and all safety precautions should be considered.

• NEVER use the laser in inflammable situation.• STAND BY position: keep the laser in the standby

position when you stopped working temporarily for any reason to prevent accidental exposure to laser surgery.

• MASKS: Special masks should be used especially when removing viral lesions to prevent inhalation of the viral particles .

ELECTRICAL HAZARDS• NEVER remove the laser protective covers.• NEVER operate the laser if there is any

leakage of water from the console. (Certain types of lasers contain water inside)

• NEVER operate the laser if the power cable is faulty

EQUIPMENT PRECAUTIONS

• Certain types of lasers contain water. The high voltage used to excite the laser and water used for the cooling system may cause dangerous hazards.

• Proper training- how the machine can work is of prime importance .

• Ensure that the operator-selected beam delivery and the beam alignment are working properly.

• Ensure that the HeNe guiding beam is working before any surgical treatment.

• NEVER fire the laser if the helium-neon beam is invisible in the field.

ANESTHESIA FOR SKIN RESURFACING

Local anesthesia• EMLA cream is composed of Lidocaine and

Prilocaine.• Regional block : used for deeper resurfacing or

sensitive patients, or wide area to be treated.• Local infiltration of the lesions by xylocaine.

Complications of laser surgery• In vascular lesions treatment, scarring may occur if too

much light energy is absorbed by the epidermis and perivascular dermis below the reticular layer of the skin.

• If the epidermis is damaged it can regenerate without scaring, while damage of the dermis may cause hypertrophic scarring.

• This is the worst complication when treating a vascular lesion as port wine stain with the use of Blue/Green wavelength especially in young children.

• Other complications are hypopigmentation, hyper pigmentation and texture changes.

SKIN CARE INSTUCTIONS AFTER LASER SURGERY

• Do not rub, scratch or put pressure on the treated area until skin changes like erythema and crusting clears.

• Do not apply make-up if there is severe reaction like oozing and blistering of the treated areas.

• Washing of the face gently by water may be allowed, while swimming is postponed for 2-4 weeks.

• The treated area should be kept away from exposure to sunlight and sun blocks should be used two weeks before and four weeks after surgery.

• Post laser hyperpigmentation and scarring are the main problems of laser surgery.

• To minimize post laser hyperpigmentation the following formula can be used by the patient two weeks before and eight weeks after laser surgery.

- 0.2% Retin A- 2% Hydrocortisone- 4% Hyroxyquinone• It can be used gently twice daily. The concentrations of the

ingredients can be modified according to the type of skin , condition of the treated area and age of the patient.

• Acyclovir tablets used 5 days before the operation in patients having history of herpes lesions.

• Oral antibiotic such as Cephalosporin can be given as a prophylactic measure.

Postoperative measures.• Apply polysporin ointment.• combination of Pufexamac and Muperacin cream

( Droxaryl & Bactropan) that proved to have an excellent post-operative healing and minimizing erythema and hyper pigmentation .

• The resurfaced area can be covered by Vaseline dressing. The dressing is left in site for 48 hours and then removed using only the medication without covering .

• Ice bags, cold milk compresses or Pufexamac cream (Parfenac, Droxaryl cream) can be applied several times a day to alleviate erythema and edema.

don’ts• Do not remove the Crusts.• Emollients such as can be used to keep the skin moist.

Washing can be permitted.• Avoiding tissue papers for drying of the skin. Soft cotton

towels can be used.• Minimize irritation of the skin by gently drying without

rubbing , just to press gently the cotton towel to the area.• Avoid irritants to the resurfaced areas such as perfumes

or strong soaps. Mild soaps can be used such as white Dove soap.

• Avoid direct sun exposure- This may lead to hyperpigmentation especially in colored individuals.

Thank you