Laser and its Applications PDF

Biophysics for First Year Students Laser and its applications Prepared by: Prof. Dr. Nabil N. Abd Allah 1  Introduction Originally LASER was an acronym for Light Amplification by the Stimulated Emission of Radiation N...

Biophysics for First Year Students Laser and its applications Prepared by: Prof. Dr. Nabil N. Abd Allah 1  Introduction Originally LASER was an acronym for Light Amplification by the Stimulated Emission of Radiation Now laser is a word used to identify this type of equipment or the light it produces. Laser is a narrow beam of light of a single wavelength (monochromatic) in which each wave is in phase (coherent) with other near it. What are the requirements to prod uce laser beam? To generate laser beam three processes must be satisfied:- – Stimulated emission. – Population inversion. – Pumping source. COLLIMATED BEAM MEDIUM MIRROR PUMP 1) Stimulated Atom is surrounded with energy levels called “ Emission atomic energy states” (e.g Hydrogen energy levels). The lowest energy state of an atom is called its ground state; higher energy states are called excited states. The atom is said to undergo a transition between two energy states when it emits or absorbs energy.  If an atom that is initially in level 1 and interacts with an electromagnetic wave of frequency n. The atom may now undergo a transition to level 2, absorbing the required energy from the incident radiation. This is well-known phenomenon of absorption. E2 hn=E2 – E1 E 1  When the atom drops back to its original energy level (orbit) it releases a particle called a photon. This is called emission process The excited atom can be reverted to a lowest state via two distinctive mechanisms: a) spontaneous emission. b) stimulated emission. a) Spontaneous emission: a) This emission takes places after the electron spent all its lifetime in the excited state. b) Each electron can drop back spontaneously to the ground state emitting photons. c) Emitted photons bear incoherent. It varies in phase from point to point and from moment to moment. This emission do not produce laser. d) e.g. emission from tungsten lamp. b) Stimulated emission: a) This emission takes places before the electron spent all its lifetime. b) Each electron is triggered into emission by the presence of electromagnetic radiation of the proper frequency. This is known as stimulated emission and it is a key to the operation of laser. c) e.g. emissionExcited from Laser state hν Ground state Note: To obtain a laser beam, more atoms have stimulated emission. Thus, population inversion must take place. 2) Population inversion It is the process by which a laser medium is excited to create more atoms in higher energy state than in the ground state. According to Boltzmann's statistics, if a sample has a large number of atoms, N o, at temperature T, then in thermal equilibrium the number of atoms in energy states E 1 and E2 are: & When N 1 > N2 This is called “Normal population" When N 1 < N2 This is called "population inversion How Population inversion takes place? We can achieve population inversion only in those systems which posses a special kind of excited state called metastable state. Meta-Stable states are energy levels have longer lifetime of the order of microseconds to a few milliseconds. If an atom is excited into a metastable state, it can stay there long enough for a photon of the correct frequency to arrive. the atoms can stay excited for longer duration resulting in steady increase in the population of the excited or metastable state and one stage we can  Life times 10-9 sec E3 E2 10-3 sec Output hn =5500 Ao (amplification) E1 Excitation E1 = Ground state, E2 = Metastable state (long life time from ms to s). E3 = Excited state (short life time ns), 3) Pumping sources: Energy pumping is provided into the laser medium. This energy is absorbed by the atoms in the medium, causing them to become excited and move to higher energy levels. the pumping method used, the key to achieving laser action is to produce a population inversion in the gain medium. Optical The pumping energysuitable pumping: can befor in liquid the form and of: solid laser because they have wide absorption bands. Electric pumping: suitable for gas laser because they have narrow absorption band. Chemical reaction.  Laser apparatus Laser apparatus is a device that produce an intense concentrated, and highly parallel beam of coherent light. The basic structure of a laser apparatus is shown in the following figure. There are three main components for any laser: active medium, pumping source, and optical resonator. Active medium or Types of lasers: Lasers are classified according to laser active medium into: Solid: for example : – Ruby (Cr:Al2O3) – Neodymium- glass (Nd-Glass). – Nd- YAG (Nd-Yttrium, Aluminum granite) Liquid lasers: (Dyes). Gas lasers: He-Ne, Ar, CO2, He-Cd, N2, Kr, Excimer (ArF, XeF, HF, DF). Ruby Laser (example of lasers) Laser Beam Properties 1. Coherent (in phase). 2. Monochromatic (single wavelength) 3. Collimated (highly parallel) 4. Intense (Concentrated) 5. Excellent frequency stability. 6. Small beam diameter (high coherence). 7. Highly-focused energy. Doppler Effect laser Doppler velocimeter Laser Doppler Velocimeter (LDV) is a technique used to measure the instantaneous velocity of a flow field. a Helium-Neon (He-Ne) or Argon ion laser with a power of 10 mW to 20 W is used. The laser Doppler velocimeter sends a monochromatic laser beam toward the target and collects the reflected radiation. According to the Doppler effect, the change in wavelength of the reflected radiation is a function of the targeted object's relative velocity. Thus, the velocity of the object can be obtained by measuring the change in wavelength of the reflected laser light, which is done by forming an interference fringe pattern.  Lasers are classified according to the hazard Class 1 and 1M (magnifier) lasers are considered safe Class 2 and 2M (magnifier) – emit visible light at higher levels than Class 1, – eye protection is provided – can be hazardous if the beam is viewed directly with optical instruments; Class 3R (Restricted) Laser – produce visible and invisible light that are hazardous under direct viewing conditions; Class 3B lasers – produce visible or invisible light that is hazardous under direct viewing conditions – they are powerful enough to cause eye damage in a time shorter – Laser products with power output near the upper range of Class 3B may also cause skin burns; Class 4 lasers – high power devices capable of causing both eye and skin burns, – heir diffuse reflections may also be hazardous – the beam may constitute a fire hazard;  Laser Therapy Laser Therapy uses specific wavelengths of light to stimulate healing and when receiving a laser therapy treatment patients do not feel a thing. Major plus: healing pain without the pain of it. The aim of laser therapy is to reduce inflammation as well as muscle fatigue and pain. As great as the treatment is, the use of the laser in treatment is only the beginning. The decrease in inflammation combined with the increase in comfort allows for a therapist to move the joint around using manual therapy more easily  Laser Interaction mechanisms the main interaction mechanism taking place during laser irradiation in medical practice: photochemical and photothermal interactions. 1)Photochemical interaction: Approximately, chemical reactions involving photons can be classified as phtotochemical reactions. The most popular example is photosynthesis; in our body other examples are the production of melanin and of the light- induced compound Vitamin D. All these reactions involve photons. The main idea of the photochemical treatment is to use a chromophore receptor acting as a catalyst 2) Photothermal interaction: The photothermal interaction is characterized by reactions that occur after a local temperature increase. In this mechanism different effects are included: coagulation, vaporization, carbonization, melting, among other effects.  Laser Tissue Light can interactInteractions: with tissue in four key ways: 1) Transmission refers to the passage of light through a tissue without having any effect on that tissue or on the properties of the light. 2) Reflection refers to the repelling of light off the surface of the tissue without an entry into the tissue. 3) Scattering refers to a change in the propagation direction without loss of energy. 4) Absorption of a photon takes place only when its energy, E = hν, corresponds to the energy difference between such quantized states. Absorption of a photon by a chromophore causes either a quantized change in the distance between charges or a quantized change of vibrational modes of the molecule.  Laser Tissue Interactions: a b LASER BEAM REFLECTION SCATTERING TARGET TISSUE Transmitting  c d e f g e- e- HEAT PHOTO- SHOCK FLUORESCENCE PHOTO- DISSOCIATION WAVE For diagnostic CHEMISTRY (Break molecular (Breaks Destroy the bond) mineralized target deposits)  TREATMENT & DIAGNOSTIC BY LASER LASER PHOTOCOAGULATION OF THE RETINA Laser photocoagulation is eye surgery using a laser to shrink or destroy abnormal structures in the retina, or to intentionally cause scarring that can help Photocoagulation certain eye conditions. can be done by: – 1- Xenon lamp – 2- Laser  Photocoagulatio n :Xenon lamp Laser 1 - Spot size 750 m m Spot size 50 mm - 1 2 - High energy deposited in the low energy deposited in the - 2 eye: 3 -20-50 times greater than eye deposited Short exposure (ms to ms) - 3 treatment by laser beam So local anesthesia are not 4 - Longer exposure (1 sec) needed than laser, so local anesthesia must be used What are the different types of laser therapy? 1)Low Level Laser therapy (LLLT) LLLT is a non-invasive light source treatment that generates a single wavelength of light. It emits no heat, sound, or vibration. It is also called photobiology or bio stimulation. LLLT is used by some physiotherapists to treat various musculoskeletal condition. LLLT in particular, is used for muscular and/ or connective tissue injuries. An output power of less than 0.5 Watts is classed as Low-Level Laser Therapy (LLLT). 2) High Level Laser Therapy (HLLT) HLLT is a therapeutic technique that utilizes a high-power laser to deliver targeted energy to the affected area. It is known for its deep tissue penetration and the ability to stimula te cellular activity and promote healing. HLLT is commonly used for pain management, tissue repair, and inflammation reduction. HLLT is particularly effective in treatment of sport injuries, e.g. muscle strain or joint distortion, and back pain caused by e.g. disc hernia or disorders in the cervical region. output power greater than 0.5 Watts are termed High level Laser Therapy ADVANTAGES OF LASER THERAPY. 1. Reduce pain. 2. Increases ATP (Adenosine Triphosphate) which accelerates the repair process of the cell. Some molecules that increase inflammation are reduced and beneficial antioxidants are increased. 3. Faster wound healing. Laser Therapy is effective on open wounds also. 4. Recovery from nerve injury Reduces aches and pains by decreasing nerve sensitivity. 5. It reduces the formation of Fibrous/Scar tissue. It also improves the vascular activity in the body. 6. Promotes bone and cartilage formation Difference between laser and x- ray