We recognize that the terminology used in discussions about laser surgery and laser science can be confusing. We have taken the time to define some of the essential terms used when discussing soft-tissue lasers, laser surgery, and laser dentistry. LightScalpel was founded by a laser physicist; our laser education expertise sets us apart from most other manufacturers. If you are finding it hard to understand laser science or laser-tissue interaction, feel free to ask us.

Laser Surgery Terms Defined

Ablation of soft tissue by laser energy: Removal of the irradiated volume of the soft tissue through the conversion of laser energy to heat, leading to intra- and extracellular water vaporization.

Ablation of soft tissue on contact with a hot tip: Removal of soft tissue by heat transfer from a hot, charred glass tip, leading to tissue decomposition (e.g., Diode).

Absorption: The transfer of radiant energy into the internal energy of absorbing tissue, resulting in a change in that tissue.

Active Medium: Any material within the optical cavity of a laser that, when energized, emits photons (radiant energy).

Attenuation: The decline in energy or power as a beam passes through an absorbing or scattering medium.

Average Power: An expression of the average power emission over time expressed in Watts; the total amount of laser energy delivered divided by the duration of the laser exposure. For a pulsed laser, the product of the energy per pulse (Joules) and the pulse frequency (Hertz).

Beam: Radiant electromagnetic rays that may be divergent, convergent, or collimated (parallel).

Beam Divergence: Angular spread of the laser beam as it propagates, affecting spot size and energy distribution at the target.

Chromophore: A substance or molecule exhibiting selective light-absorbing qualities, often to specific wavelengths.

Class IV Laser: A surgical laser that requires safety personnel to monitor the nominal hazard zone, eye protection, and training. This class of laser poses a significant risk of damage to eyes and any non-target tissue and can produce plume hazards.

Coagulation: An observed denaturation of soft tissue proteins that occurs at 60°C.

Coherence: Fixed phase relationship between the electric fields of laser photons, enabling high beam collimation and interference effects.

Contact Mode: The direct contact of a charred hot glass tip (of a diode or Nd:YAG laser) to the target tissue.

Continuous Mode: A manner of applying laser energy in an uninterrupted (non-pulsed) fashion, in which beam power density remains constant over time; also termed continuous wave, and abbreviated as ‘CW.’ Contrast with ‘Pulsed Mode.’

Curettage: Scraping of tissue from a surface or cavity using a curette or laser ablation to remove lesions or granulation tissue.

Debridement: Removal of devitalized or necrotic tissue by laser energy or sharp instruments to promote healthy wound healing.

Dissection: Separation of tissue layers using laser energy or sharp instruments to isolate anatomical structures.

Duty Cycle: Ratio of laser “on” time to total cycle duration, expressed as a percentage or fraction, determining average power delivery.

En Bloc Resection: Removal of a lesion and surrounding margin as a single intact specimen using laser energy or surgical instruments to ensure complete excision.

Energy: The ability to perform work, expressed in Joules. The product of power (Watts) and duration (seconds). 1 Joule = 1 Watt x 1 second.

Energy Density: The measurement of energy per area of spot size, usually expressed as Joules per square centimeter; also known as fluence.

Excision: Removal of targeted tissue by laser ablation or mechanical means, excising pathological or unwanted tissue for treatment or biopsy.

Fluence: See Energy Density.

Free-Running Pulse Mode: A solid-state laser operating mode where the emission is truly pulsed and not gated. A flashlamp is used as the external energy source, allowing for very short pulse durations and peak powers of thousands of watts. A laser operating in this mode cannot be operated in a continuous wave.

Gated Pulse Mode: A laser operating mode where the emission is a repetitive on-and-off cycle. The laser beam is emitted continuously, but a mechanical shutter or electronic control ‘chops’ the laser beam into pulses. This term is synonymous with chopped pulse mode.

Incision: A precise cutting of soft tissue by laser energy or an instrument to create an opening for surgical access.

Intensity: See Power Density.

Irradiance: See Power Density.

Joule: See Energy. A unit of energy or work equal to an exposure of 1 Watt of power for 1 second.

Nominal Hazard Zone (NHZ): Spatial region around a laser within which irradiance or radiant exposure exceeds the maximum permissible exposure, requiring access restrictions.

Non-ablative: A mode of laser-tissue interaction in which energy is delivered below the ablation threshold, inducing thermal coagulation or remodeling without vaporizing tissue.

Noncontact Mode: A laser technique in which the delivery system is used without touching the target tissue; light radiation may be defocused or focused, depending on the operator’s technique and procedure.

Optical Density (OD): Measure of the attenuation provided by protective filters or eyewear, indicating the logarithmic reduction of laser irradiance at specified wavelengths.

Peak Power: The highest power in each pulse.

Photodisruption: Induction of mechanical tissue rupture by high-intensity laser pulses creating plasma and shock waves, allowing precise cutting with minimal thermal spread.

Photomechanical (Photoacoustic) Effect: Generation of mechanical stress and acoustic waves in tissue due to rapid thermoelastic expansion following laser pulse absorption.

Photothermal Effect: Conversion of absorbed laser energy into heat within tissue, resulting in protein denaturation, coagulation, or vaporization.

Plume: Essentially, the smoke is produced from aerosolization of by-products due to laser-tissue interaction. It is composed of water vapors (the dominant component) and particulate matter, including cellular debris, carbonaceous and inorganic materials, and potentially biohazardous products.

Power: The amount of work performed per unit time, expressed in Watts (Joules per second). 1 Watt = 1 Joule / 1 Second.

Power Density: The measurement of power per area of spot size, usually expressed as Watts per square centimeter; also known as intensity, irradiance, and radiance.

Protective Eyewear: Specialized goggles or glasses with defined optical density and wavelength filtering worn to prevent ocular injury from laser exposure.

Pulse Duration: A measurement of the total amount of time that a pulse is emitted; also known as pulse width.

Pulsed Mode: Laser radiation that is emitted intermittently as short bursts or pulses of energy rather than in a continuous fashion. Contrast with ‘Continuous Mode.

Repetition Rate: Number of pulses per second, also known as pulse rate; usually expressed in Hertz (Hz).

Scattering: The beam disperses throughout the tissue in all directions.

Smoke Evacuator: A device that captures and filters the plume produced during laser-tissue interaction by applying localized suction through a nozzle and passing the smoke through high-efficiency filters to remove particulate and gaseous by-products, maintaining a clear operative field and reducing airborne hazards.

Soft-Tissue: includes skin, tendons, ligaments, fascia, fibrous tissues, fat, muscles, and synovial membranes.

SuperPulse: A variation of high peak power pulsed mode producing char-free tissue ablation, in which the pulse durations are shorter than Thermal Relaxation Time, and pulse spacing is greater than Thermal Relaxation Time.

Thermal Relaxation Time: The rate at which the irradiated tissue diffuses the heat away from the irradiated volume of the tissue defines the Thermal Relaxation Time. The wavelength-dependent absorption coefficient controls this value.

Vaporization: conversion of liquid water into vapor.

Wavelength: Distance between successive peaks of the electromagnetic wave emitted by the laser, governing tissue absorption characteristics.