basics of lasers

Basics Of Lasers:

Definition:

“LASER” is an acronym that stands for Light Amplification by the Stimulated Emission of

Radiation.

Laser is an instrument that generates a beam of light of a single wavelength or color that is both highly collimated and coherent.

Principle of laser:

BASICS COMPONENTS OF LASER:

History:

• The first functional laser (ruby, 694 nm) was developed by Maiman in 1960.

Characteristics of Laser Light:

Monochromatic: composed of a single wavelength or color.

Coherence: All the waves of light move together temporally and spatially.

Collimation: where the transmission of light occurs in parallel fashion without significant divergence, even over long distances.

Electromagnetic Spectrum:

Lasers Commonly used in Dermatology:

1. Argon Laser: 488/514 nm2. Potassium-titanyl-phosphate (KTP): 532 nm 3. Copper bromide/vapour: 510/578 nm 4. Argon-pumped tunable dye (APTD): 577/585 nm 5. Krypton: 568 nm6. Pulsed dye laser (PDL): 585/595 nm 7. QS ruby: (694 nm)

8. QS alexandrite: (755 nm) 9. QS neodymium (Nd):yttrium- aluminum-garnet

(YAG): 1064 nm 10. Erbium:YAG: 2940 nm 11.Carbon dioxide Laser: 10,600 nm

VISIBLELIGHTINFRARED

Terminology:

Power: The rate at which energy is emitted from a laser. Watts.

Joule (J): A unit of energy used to describe the rate of energy delivery.

Fluence: determines the amount of laser energy per unit area and is expressed in joules/cm2.

Spot Size: The mathematical measurement of the radius of the laser beam.

Pulse: A discontinuous burst of laser as opposed to a continuous beam. Pulse Frequency: The rate at which pulses are generated. Is expressed in pulses per second (Hz).

Pulse Duration: The "on" time of a pulsed laser. Measured in terms of ms, μs, or ns.

Irradiance: (power density) The rate at which energy is delivered per unit area.It determines the ability of a laser to incise, vaporize, or coagulate tissue and is expressed in watts/cm2.

Thermal Relaxation Time(TRT): time required for the dissipation of 63% heat gained by the tissues (ms/μs) during irradiation.

Thermal Damage Time(TDT): The time for the entire target including the primary chromophore and surrounding target to cool by 63%.

Focus: The exact point at which the laser energy is at peak power

63%

Chromophores in the Skin:Are the selectively laser energy absorbing target molecules in the skin.1. Endogenous chromophores: • Melanin: UV -1200nm • Hb: UVA, blue (400 nm), green (541 nm), Yellow (577nm)• Collagen: Visible and near infra-red spectra• Water: in the mid and far infrared regions2. Exogenous chromophores: Such as tattoo ink.

Classification of Lasers:

Laser are classified according to the nature of the amplifying medium: gas, liquid(dye) or solid state:

Modes Of Output:

• Continuous wave • Quasi CW• Pulsed

Ablative Vs Non Ablative:

ABLATIVE: outer layers of skin are (removed) through vaporization of the cells. Healing takes place by re-deposition of collagen.Egs:Er: YAGCO2 laser

NON-ABLATIVE: induce dermal neocollagenesis without epidermal disruption,KTP Pulsed Dye Nd: YAG

FRACTIONATED LASER:Laser beam is “fractionated” into a pattern where some parts of the skin are targeted, and the other parts are left intact. A grid like pattern appears on the skin.

How Fractionated Lasers Work:

Tissue optics:

Tissue optics:

1. Reflection. • 4–6% of light is reflected.• Lowest when the beam is perpendicular.

2. Absorption. Depends on the propertiesof the substance through which the light passes. Target molecules are called chromophores:(1) Melanin(2) Hemoglobin(3) Water(4) Collagen

3. Scattering. Is the deviation of light by non-uniformities in the medium Eg: collagen in the dermis.It reduces the energy available for the target chromophores.

4. Transmission. Light that is not Reflected, absorbed or scattered passes to deeper tissue.

Light–tissue interaction:

1) Photostimulation: Low energy lasers expedite wound healing.

2. Photodynamic change: uses topical or systemic photosensitizers. Subsequent irradiation elicits a photo-oxidative reaction and an immediate cytotoxic effect.

3) Photo-thermolytic and Photo-mechanical Effect: works on the principal of Selective photothermolysis: A concept used to target chromophore based:

• on its absorption characteristics, • the wavelength of light used, • amount of energy delivered.• the duration of the pulse,

4. Photo Acoustic Effect:

Uses of Laser: Lasers

1. Hair Reduction: Long pulsed Nd:Yag (1064nm)

Alexandrite laser (755nm)

2. Hyperpigmentation:

(a) Epidermal Type Q switched, Nd:Yag (532nm)

PDL

Uses of Lasers:

(b) Dermal Type: Q switched Nd:Yag (1064nm)(c) Mixed Type: Q-switched Ruby (694nm)

Chromophore: Melanin

Chromophore: Melanin

(c) Large Vessel TelengiectasiaKrypton Laser (568nm)Copper vapour Laser

3. Vascular Lesions:

(a) Port wine stain PDLAlexandrite laser (755nm)Q switched Nd:Yag (1064nm)

(b)Small calibre Telengiectasia PDL

Chromophore: Hemoglobin

(4) Facial Rejuvenation:

(a) Ablative: CO2 laser(10,600nm)Erb:Yag laser (2940nm)

(b) Non-Ablative:PDLQ-switch Nd:Yag (1064,532)

(5) Hypertrophic scars, warts, benign neoplasm

PDL

(7) Acne PDL

(6) Hemostasis CO2 Laser (10600nm)(7) Laser Lipolysis: Nd: Yag Laser (1064nm)

Chromophore: Water

(8) Tattoos:

(a) Blue/ Black Q-switched ruby, Q-switched alexandriteQ-switched 1064-nm Nd:YAG

(b)Green Q-switched ruby, Q-switched alexandrite

(c) Red/ Orange/ Purple Q-switched Nd:YAG 532-nm

Chromophore: Tattoo Ink

Cooling Systems:

Cooling Systems:Contact skin cooling • Active

Copper, or sapphire tips:For delivering longer pulse durations(>10 ms)Provide pre, parallel and post laser cooling.

• Passive Ice cubes:

Reduces inflammation post procedure. Easy method. Disadvantages: a waiting period Melting water on the skin

Aqueous gels: Not advised nowadays. Cannot provide prolonged cooling.

Non Contact Cooling:

1) Cryogen spray (liquid nitrogen):(a) Not recommended now causes cryonecrosis.

2) Pulsed cryogen spray (dynamic cooling device):(a) Provides uniform cooling at -30C(b) Method of choice

3) Forced refrigerated air:(a) Delivers chilled air pre, parallel and

post procedure. (b) By convection cooling.

Preparing A Patient for Laser session:

Patient selection:1. Take History to find out:

• Immunocompromised status, esp diabetes • Isotretinoin use. • Active local or systemic infections especially recurring HS infection. (Aciclovir or valaciclovir given 1 day prior to & 5–14 days post treatment) • Tendency to keloid scarring. • Personal or family history vitiligo.

2. Prophylactic antibiotics and antivirals for ablative procedure3. To minimize post laser hyperpigmentation: 2 weeks before and 8

weeks after laser:0.2% Retinoid preparation2% Hydrocortisone4% Hyroxyquinone

Anesthesia:Topical anesthetic ointment under occlusion for 1 hr.For ablative procedures, nerve blocks, tumescent anesthesia.

Contraindications:

Absolute:

• Active bacterial,viral or fungal infections• Unrealistic expectations• Uncooperative pts• Malignancy

Relative:

• Immunocompromised: Diabetes, HIV, Hepatitis B,C• Oral isotretinoin• Fitzpatrick skin 5-6 phototypes• History of keloids.• Patients taking gold salts are at the risk of chrysiasis (gold-

related skin discoloration).

Precautions:

Precautions:

The operating room:• Laser room should be properly labeled. • Hang eye goggles on the door.• Unauthorized people should not be allowed.• The room should not contain volatile substances such as

ether, alcohol .• Plume evacuator: for larger lesions and warts.

Safety measures for the patient:• Special glasses should be used.• Patient Consent

General measures:• The surgeon should use the special glasses for the

particular laser.• NEVER look directly into the laser source.• NEVER point the hand probe in any direction, except

towards the area to be treated.

SKIN CARE INSTUCTIONS AFTER LASER SURGERY:

• Do not rub, scratch or put pressure on the treated area• Do not apply make-up in case of severe reaction.• Avoid sunlight; Sun blocks can be advised.• Ice bags to alleviate erythema and edema.• Emollients to keep skin moist. • Avoid irritants to the resurfaced areas• Erythema and edema settle with topical corticosteroids

SIDE EFFECT OF LASERS:

Side Effects of Lasers:

(1) Immediate:• Pain, burning sensation, edema

(2) Early:• Oozing, crusting• Secondary infection• Reactivation of HS infection

(3) Late:• Dyspigmentation (hypo/hyper)• Change in skin texture• Demarcation lines

(in facial rejuvenation)• Keloids and hypertrophic scars• Scarring• Milia• Persistent erythema• Dilated follicular ostia

Nd: Yag Laser:

Nd:YAG (neodymium-doped yttrium aluminum garnet) is used as a laser medium.• Wavelengths: 532nm and 1064 nm, • Penetrates 2-3mm into dermis

QSNd:YL 1064-nm:Has the least absorption by melaninDeepest penetration. Effective for both epidermal and dermal pigmented lesions.

QSNd:YL 532-nm:Is well absorbed by both melanin and hemoglobin. Has superficial penetration,Limited to treating epidermal pigmented lesions.

Vascular lesionsSpider and thread veins Varicose veins Telangiectasia Haemangioma

Pigmented lesionsSolar lentiginesFrecklesNevus of Ota and ItoMongolian spotCafé-au-lait-macules.

Hair removal:

Tattoos:

Pulsed Dye Laser:

• Contains a rhodamine dye • Wavelength: 585–600 nm.• Pulse duration:0.45 ms (short-pulse)

1.5–40 ms (long-pulse PDL) • Penetrates the dermis to a depth of 1.2 mm &

photocoagulates vessels of up to 100 μm in diameter.

• Primary chromophore: hemoglobin.

USES:

Cutaneous vascular lesions:• Port wine stains• Superficial hemangioma• Telangiectasia

Non-vascular skin conditions• Plane warts• Pyogenic granuloma.• Melasma • Hypertrophic scars• Nail psoriasis/plaque psoriasis

Carbon Dioxide Lasers:

Active laser medium: 10–20% carbon dioxide,

Exists as Ablative nonfractinated laser Ablative fractinated laser

Wavelength: 10,600 nm Primary chromophore: Water

• Depth: 20-30 µm of skin (epidermis and superficial papillary dermis)

• In the healing period: re-epithelialization

The following skin disorders can be treated with carbon dioxide laser beams:• Rhytides• Acne scars• Varicella and smallpox scars• Verruca vulgaris/plana• Junctional & compound Nevi• Small syringomas

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