LASER ( Part 1)

1. LASER(Part 1) Prof.Dr.GehanMosaad

2. At the end of the lecture the student should be able to • Define laser and know its physical properties • Discuss the mechanism of LASER production • Identify different classification of LASER • Understand the therapeutic effects of LASER • Know indications and contraindication of LASER. • Identify the techniques of applications

3. LASER THERAPY Laser is one of the most recent treatment modalities available to physiotherapists. Definition It is a special form of electromagnetic energy. It has a specific wave length and therefore a specific energy. The word LASER is an acronym for: • L ——» Light, • A ——» Amplification, by • S ——» Stimulated, • E ——» Emissions, of • R ——» Radiation. It refers to the production of a beam of radiation which differs from ordinary light.

4. Physical properties of LASER There are three main characteristics of laser light that clearly differentiate it from ordinary light. 1- Monochromaticity • Ordinary light consists of many wave lengths • Laser light consists of only one wave length • It means that each type of laser essentially produces only a single wavelength of light with a single color. • Laser effect is a wavelength specific.

5. Physical properties of LASER (cont.) 2- Coherence • Laser light comprises the identical wave length and forms that cause it to be greatly amplified. • Laser radiation are coherent both temporal and spatial. • Temporal coherence means that the beaks and troughs of the electric and magnetic fields all occur at the same time. • Spatial coherence means they are all traveling in the same direction.

6. Physical properties of LASER (cont.) 3- Collimation (Non-divergence) • It simply refers to degree of parallelism of the beam. • Ordinary light shines in all directions • Laser light shines only in one direction. • Laser beam is highly collimated which has very little divergence LASER

7. Physical principles of Laser production Laser is produced by a device that amplifies or increases the intensity of light producing a strong, highly directional or parallel beam of light of a specific wavelength. Basics of atomic theory are used to explain the principles of Laser generation The atom is composed of a nucleus at its center, which contains positively charged protons and neutrally charged neutrons. Moving about the nucleus are electrons, which are negatively charged and are bound to the nucleus by the electromagnetic force.

8. Physical principles of Laser production (cont.) • An electron will stay in its lowest energy level (ground state) unless it absorbs an adequate amount of energy ( photon) to move it to one of its higher orbital levels E1, E2, E3. When this occurs, the atom is said to be in an excited state. This process is called absorption or excitation • NB: The electron changes orbit, when it either gains or loses a distinct amount of energy, it can not exist between orbits. • The atom stays in this excited state only momentarily and releases an identical photon (energy) equal to the one it absorbed, which returns it to a ground state. This process is called spontaneous emission

10. Physical principles of Laser production (cont.) • When the released or emitted photon collides with another atom in an excited state causing it to emit another photon. • The end result is the emission of two identical photons and the return of the electron back to the lower energy state. • These two photons will promote the release of additional identical photons (having same frequency, direction and phase) as long as other excited atoms present. This process is called stimulated emission. • This occurs when having an environment with unlimited excited atoms, which is termed population inversion that means presence of many atoms in an excited state rather than in a ground state. • Population inversion is caused by applying an external power source to the lasing medium. • This is the principle of operation of a laser (which stands for Light Amplification by Stimulated Emission of Radiation): one photon comes in, two photons come out.

11. Production of LASER • Laser production requires the following components: 1- Lasing medium ——» materials that generate the laser light which is capable of absorbing energy and subsequently give off excess energy as photons of specific wave length. 2- Power supply ——» energy source to excite lasing medium. 3- Resonating cavity ——» mirrored chamber or tube contains the lasing medium. Mirrors are placed at both ends of tube. One mirror is totally reflective, whereas the other mirror is partially reflective . It is not as pure mirror thus does not reflect 100% of the light striking its surface.

12. Laser production components

13. Production of LASER (cont.) • The steps of laser production include: 1- Excitation( absorption): When a tube filled with mixture of gaseous (helium and neon) is stimulated electrically, their atoms become excited. As the incident photon is absorbed by resting electron of lasing media which move it to higher energy level. 2- Spontaneous emission: TheExcited electron drops to lower resting level (E1) emitting single photon of specific wavelength depending on the lasing medium. 3- Stimulated emission: Incident photon interacts with already excited electron to produce two identical photons.

14. Steps of Laser production

15. Production of LASER (cont.) • The production of photons are concentrated within the chamber as they are reflected by the mirrors located at its ends, which amplifies the light and stimulates the emission of other photons from excited atoms. • When a specific level of energy is attained, photons of a particular wavelength are ejected through the partially reflective mirror at one end of chamber. Thus amplified light through stimulated emission (LASER) is produced.

16. Production of LASER

17. Classification of laser I- It can be classified according to the active medium (material) utilized:- 1. Solid state lasers:- e.g: neodymium lasers 2. Gas lasers:- e.g - He-Ne: which is the first gas laser used in red laser - Ionic gas laser, —> argon - Molecular gas laser. - Chemical laser. 3. Semiconductor laser :- or diode laser. Emitting the I.R.) e.g) - Gallium – Arsenide (Ga-As) - Gallium – Aluminum (Ga-Al) - Ga- Al - As. 4. Liquid (dye lasers). 5- Free: Electron laser ——> very high power. 6. Metal vapor lasers, e.g Helium cadmium & Copper vapor.

18. Classification of laser(cont.) II- It can also be classified according to the amount of output power and wavelength output deliver. 1. High power lasers (Hot): e.g., Co2 laser. • High intensity LASER • It generates heat and destroys only selected tissue directly in the beam while avoiding damage to surrounding tissues. • Hot laser has a cutting power so, it is used clinically to make incisions in surgical procedures.

19. Classification of laser(cont.) 2. Mid power laser: (cold) e.g., I.R.laser. • This type of laser used by physical therapist. • Low intensity laser. • It doesn't generate heat or destroy the tissues. • This form of laser may be biostimulative and facilitate healing. • Mid power laser has 2 main types: a- Helium neon (He Ne): has superficial effect (0.8-1.5mm). b- Infra red (IR): has deep effect with penetration up to 30 mm. 3. Low power lasers: soft laser. This type of laser used by dermatologist.

20. III- It can also be classified according to the potentialdanger posed to the exposed skin and to the eye into four classes.

21. Laser tissue interaction • Therapeutic laser-tissue interaction is essentially ATHERMIC (non thermal). • The main type of reaction with tissue during laser therapy would appear to be PHOTOCHEMICAL. • The absorption of the incident photons by irradiated tissue produces chemical rather than thermal energy. • Once Laser is directed at the tissue, it may be reflected, transmitted, scattered and absorbed in proportion that depends on • The angle of incidence • The wavelength of the radiation • The nature of the tissues irradiated

22. The photochemical theory • It stated that the absorption of laser light take place in tissues chromophores (photoacceptores) • These chromophores may be enzymes, a membrane molecule, or any other cellular or extracellular substances, thereby producing a stimulation of cell activity. • Activation of these chromophores by laser light is thought to be responsible for laser biostimulation effect.

23. Physiological Effects of laser radiation on the tissue Any physiological effects of lasers occur at the cellular level and are produced by photochemical means. It has been proposed that lasers stimulate or inhibit biochemical, physiological, and/or proliferative activities by altering the intercellular actions and interactions. • Cellular effects • Increased ATP and nucleic acid production • Stimulation of macrophages • Stimulation of fibroblasts to increase collagen production • Altered nerve conduction and regeneration • Vasodilatation