Low intensity LASER therapy

One of the most recent treatment modalities available to physiotherapists is that of the laser. LASER is an acronym for light amplification by stimulated emission of radiation.

A laser is generally used as a source or generator of radiation. The low power laser is used in physical rehabilitation for pain control and soft tissue injury.

Radiation is the process by which energy is propagated through space . the common characteristics of all forms of radiant energy are-

  • They are produced by applying electrical or other forces to various forms of matter.
  • They all may be transmitted without the support of sensible medium.
  • Their velocity of travel is equal in a vacuum but may vary within different media.

The direction of propagation is normally a straight line. They undergo reflection, deflection and absorption by the media through which they travel.

They are designated collectively as electromagnetic radiations.


  • Albert Einstein, originally outlined the principles underlying the generation of such light by 1917 as part of the quantum theory.
  • In 1960 Theodore Maiman produced the first burst of ruby laser at Hughes laboratories in USA.
  • Laser for medical use development between 1960s to 1970s by professor ender mester’s group in Budapest, their work indicated the potential of relatively low-intensity laser irradiation applied directly to tissue, to modulated certain biological processes- in particular the photobiostimulative wound healing process( mester and mester,1985 ).


Low intensity laser therapy is a therapeutic application of relatively low output (<500mW) laser and monochromatic super luminous diodes for the treatment of disease and injury.

  • This modality at low-intensities does not produce heat in the tissue ( athermal ), it is sometimes called as the cold or soft laser.
  • Biological mechanism involved to get the beneficial effects of this modality is called laser photobiomodulation.


There are three characteristics of laser emission, that make it clearly distinct from ordinary light.

A) Monochromaticity

  • ordinary light consist of many wavelengths, commonly know as VIBGYOR  I.e. violet, indigo, blue, green, yellow, orange,red which merge to form white light.
  • But laser consist of one wavelength only.
  • The laser of 6328 A units is of bright red colour.


B) Coherence

  • Two wave source are perfectly coherent if they have a constant phase difference and the same frequency.
  • The wavelength of ordinary light are so variable and do not match in wave forms, frequencies, or shapes, there Is much scrambling of wave forms, cancellation and reinforcement of individual waves.
  • This factor minimize the power of ordinary light as an energy source.
  • The identical wavelength and forms, that comprise laser light cause it to be greatly amplified or radiation are reinforced because they are parallel and in line with each other, they are termed coherence.
  • The light emitted by laser devices are in phase i.e. the troughs and peak of the emitted light waves match perfectly in space ( spatial coherence )and time (temporal coherence ).


C) Collimation ( to make parallel, line up)

As a consequence of spatial coherence, laser remain in a parallel beam, because radiation do not diverge the energy even if propagated over very long distance.


Production of laser based on , spontaneous emission, absorption and stimulated emission of light

Laser light is produced:-

-When an electron of an active medium undergoes a stimulated quantum Jump. From a higher to a lower energy state-causing the emission of photons.(spontaneous emission)

-The incident photons is absorbed by the resting electron, which moves to the higher energy level.( absorption)

-The emitted photons collid with other excited electrons causing more photon emission (stimulated emission)

This chain reaction produces laser light.


On the basis of their power and effect-

A) Class-1

  • low power ( < 0.5mW ) device.
  • Operating in the visible and invisible region of the electromagnetic spectrum.
  • Do not cause any danger to the eye or skin.
  • Not used for therapeutic application .
  • Used primarily for black board pointers.

B) Class-2

  • power output up to 1mw.
  • Placed in the visible region of the electromagnetic spectrum.
  • Safe for skin.
  • Limited clinical applications in therapeutic.
  • Also used as laser pointer.

C) Class-3

  • Mid power laser of both visible and invisible range.
  • Further classified in:-
  • 3A-low medium laser with power output up to 5mw.
  • 3B– medium laser with power output up to 500mw.
  • Used in therapeutics as well as laser pointers.
  • Safe for the skin but harmful for eyes.
  • It necessitates the use of protective goggles by both the therapist and the patient.

D) Class- 4 & 5

  • High power laser such as the CO2 lasers.
  • Having a power output of >500mw.
  • Unsafe to both the eye and the skin.
  • Unsuitable for therapeutic applications.
  • However, these are used for surgical application.

THE ARNDT-SCHULTZ LAW ( conceptual basis for laser photobiomodulation)

  • The photobiological effects of laser upon the tissue are many and complex and poorly under stood particularly in terms of the variable stimulative inhibitory reaction.
  • In providing a theoretical basis for the observed biological and clinical effect of this modility, the arndt-schultz low has been proposed as  a suitable model.


As in evident in the fig. at the point of pre-threshold (A), no biological  activation occurs; where as at the point (B) when the intensity reaches a particular therapeutic valve, there is a maximum activation of the biological process.

As the intensity is increased further,i.e. a (C) there occurs bio-inhibition the biological process is inhibited.


A) Ruby laser

  • This consists of a small synthetic ruby rod made of aluminium oxide.
  • A helical xenon flash tube, wound around it, gives an intense flash of white light.
  • Both and of rod are made flat and silvered, one end being totally reflecting and the other partially transparent so that some radiation can be emitted.
  • This brief light pulse (0.5ms) excites the ruby molecules and raises many electrons to higher levels
  • The electrons stay in the heigher level for a short time,before falling to the metastable level where they stay for a longer time.
  • A stage comes, when there are more electrons in the metastable level than the ground level, which is called ‘population inversion’.
  • The process rapidly accelerates as more and more photons are released i.e.stimulated emission of radiation occurs.

The photons, having a wavelength of 694.3nm,which is of course red light, are reflected up and down the short ruby rod, rapidly increasing the effect.

Helium-neon laser

  • Helium-neon lasers consist of a long tube containing these natural gases at low pressure surrounded by a flashgun tube, as described for the ruby laser.
  • Excitation of these atoms leads to different energy levels between them and the transfer of energy, giving off a photon of wavelength equivalent to the energy gap.
  • The photons are reflected to and fro along the tube, giving rise to further photon emission and emerging as a narrow beam (of about 1mm diameter) from the partially transparent end.
  • Helium-neon lasers give radiation in the red visible region at 632.8 nm.
  • The output is usually applied to the tissues via an optical guide- a fibreoptic cable-the end of which is held in contact with the tissues.
  • There, are, of course, some energy losses in the glass fibre of the cable and the laser beam may diverge to some extent as it emerges at the end of the optical fibre.

Diode laser

  • These are specialized light-emitting diodes, based on semiconductor p-n junctions.
  •  They are of various kinds, involving gallium aluminium arsenide.
  • In these, electrons can flow more readily in one direction than in the other.
  • The electrons are excited by the application of a suitable electrical potential and their occupation of ‘holes’ in the crystal lattice arrangement may lead to the emission of a photon, which may then stimulate identical photons
  • The photons are reflected to and fro and emitted as a laser beam from one partially transparent end.
  • These are conveniently small, relatively cheap and robust devices.
  • by varying the ratio of gallium to aluminium, such devices can be built to emit specific wavelength.



  • Measured in nanometer (nm)
  • Higher the wavelength, the deeper it penetrates.
    • 670nm→open wound, ulcers, bedsores.
    • 780nm→superficial muscular or ligament lesions.
    • 820nm→muscular or ligament lesions.
    • 850nm→deeper muscular or ligament lesions.

2) Power:-

  • Denoted by P
  • Measured in milliwatts (mW)

3) Treatment:-

  • Denoted by T
  • Measured in seconds (s)

4) Energy:-

  • Denoted by E
  • Measured in joules( J ).
  • This is calculated by multiplying treatment time and power.
  • Energy expressed in joules and the amount of energy on a surface is expressed in joules per square meter.

5) Energy density:-

  • To express the average power per unit area (J/cm²) , the term ‘energy density’ is used.
  • This is calculated by (power × treatment time) / spot size.
  • Typical value for routine treatment may range from 1-10 J/cm².
  • But dosages as low as 0.5 J/cm² upto 48 J/cm² have been suggested for use.

6) Spot size:-

  • Measured in centimeters squared (cm²).
  • This is the area being irradiated by the laser beam.


Laser Photons visible red light absorbed within mitochondria (infrared light absorbed at the cell membrane)  Single oxygen production (Rate limiting mechanism operate to prevent excess single oxygen formation)  Formation of proton gradients across cell membrane of mitochondria  Physiological changes-1) changes in cell membrane permeability; 2) increase ATP levels- DNA production; 3) influences cell metabolism.  Activation of regulatory process, ⇒  Patient’s well being (after laser therapy).

→Result of laser therapy has shown:

  • Increase-
    • Macrophages  ⇒  Tissue repair
    • Fibroblasts  ⇒  Tissue repair
    • Endotheliocytes ⇒  Tissue repair
    • Keratinocytes   ⇒  Tissue repair
    • Mast cells  ⇒  Tissue repair  and pain reduction
    • Angiogenesis  ⇒  Tissue repair
    • Collagen synthesis  ⇒  Tissue repair
    • Myofibroblast activity  ⇒  Tissue repair
    • Serotonin  ⇒  Resolve inflammation and pain reduction.
  • Nerve conduction-
    • Latency  ⇒  Pain reduction (via nerve conduction)
  • Decrease-
    • Bradykinin  ⇒ Pin relief
    • Activity in C fibers  ⇒ Pain relief (via nerve conduction)


  • Wound healing (ex- surgical wounds, pressure ulcers etc.)
  • Arthritic conditions (ex- osteoarthritis, rheumatoid arthritis.)
  • Musculoskeletal disorders (ex- Myofascial pain, lateral epicondylitis etc.)
  • Pain (ex- Myofascial trigger points, carpal tunnel syndrome)
  • Edema relief (ex- edema in knee joint following ACL injury)
  • Raynaud’s disease (ex- Raynaud’s disease)


  • Reduction of edema and hyperaemia.
  • Promote of wound healing( in such conditions as necrosis of the pulpae)
  • Relief of pain of various etiologies including dentine hyperaesthesia, acute pulpitis and pre-operative and post operative pain.
  • Treatment of herpes labialis ( cold sores) and herpetic gingival stomatitis.


  • Do not radiate the age directly.
  • Certain patient are not treated with laser e.g. epileptics.
  • Cardiac patients and patient with pace maker are not treated in the chest region.
  • Photosensitive patient.
  • Patient with active or suspected carcinoma.
  • With in 4-6 months following
  • Areas of hemorrhage.
  • Locally to the endocrine glands.
  • Direct irradiation over the pregnant uterus.
  • Skin infection.


poor results may ensure in those patients:-

  • Extreme age
  • Under heavy medication
  • With thick eschar
  • With considerable scar tissue
  • With extremely dry skin
  • With active infection


The low intensity laser can be applied to the body by either of the three methods, such as:

  1. Probe:
    1. Most low intensity laser sources are applied to the skin by a hand held applicator about the size of a large marker pain.
    2. Direct application to the skin ensures maximum transfer of laser energy and the light pressure by squeezing blood from superficial vessels can increase the penetration further.
  2. Cluster probe:
    1. A collection of individual laser diodes emitting at different wavelengths.
    2. The advantage of using cluster probe is that, it can be used to treat a larger area of approximately 25 cm².
  3. Scanner applicator:
    1. The laser applicator is attached to a stand up to 30 cm away from the skin
    2. The applicator can have several sources of laser output and is moved either mechanically or manually in a systematic path over the area to be treated.

Techniques of application

What ever may be the method,  the following procedures should be followed:

Preparation of the patient-

  • The nature of the treatment and the need to wear goggles or spectacles are explained to the patient.

Preparation of the apparatus-

  • The laser probe is selected depending upon the nature and size of the lesion.
  • In case of localized lesions where the skin is intact, a probe is selected; and for large areas with intact skin, a cluster probe is the choice.
  • In case of open wound with damaged skin, the laser scanner applicator is used.

Preparation of the part-

  • The surface of the skin to be treated is cleaned with an alcohol wipe in order to remove any material on the surface
  • The part is supported in such a way that any pressure of the laser applicator does not cause movement or discomfort.


  • A key usually activates the machine and ensures that the unauthorized people do not switch the laser on.
  • The laser applicator is applied to the surface before switching on.
  • If a larger area is to be treated,  applicator is removed and re-positioned on a new site, turning off the output during the transfer.


  • the device is switched off  before removing the applicator from skin contact.
  • the details of dosage and any patient response, such as immediate increase or decrease of pain, are noted and recorded, plus the parameters of dosage.
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