Medical Biophysics, Chapter 3, Laser Presentation PDF

‫الفيزياء الحيوية الطبية‬ Medical Biophysics CHAPTER (3) LASER  Lesson Objectives: By the end of this chapter, a student will be able to : 1-Name the Lasers (A new light source). 2-Find Types of Lasers (A new light source). 3-Calculate the Spring Force. 4-Classify Principles...

‫الفيزياء الحيوية الطبية‬ Medical Biophysics CHAPTER (3) LASER  Lesson Objectives: By the end of this chapter, a student will be able to : 1-Name the Lasers (A new light source). 2-Find Types of Lasers (A new light source). 3-Calculate the Spring Force. 4-Classify Principles Of Laser Action. 5-Recognize Low Level Laser Therapy. 6- Find Causes Of Laser Accidents & General Safety Practices. Things you need to know Before studying about lasers, you must be familiar with basic terms used to describe electromagnetic waves: Wavelength (λ) Frequency (f) Period (T) Velocity of light ( c ) Index of refraction (n) Wavelength (λ) It is the distance between two points on the wave, which have the same phase Frequency(f) Number of complete cycles in one second (Hertz). c = v * f Periodic time (T) Time required making one complete cycle (S). Speed of the light c = 300,000 [km/sec] = 3*10 8 [m/sec] = 186,000 [miles/sec]  Laser Light Amplification by Stimulated Emission of Radiation laser -1A laser is a device that emits light (electromagnetic radiation) through a process called stimulated emission. -2The term laser is an acronym for light amplification by stimulated emission of radiation. 3-Lasers used in research, medicine, industrial, commercial applications.  laser LASER SPECTRUM Gamma Rays X-Rays Ultra- Visible Infrared Micro- Radar TV Radio violet waves waves waves waves 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102 Wavelength (m) LASERS Retinal Hazard Region Ultraviolet Visible Near Infrared Far Infrared 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 10600 Wavelength (nm) ArF XeCl HeNe Ruby Communication CO2 193 308 633 694 Diode 10600 KrF Ar 2 Alexandrite GaAs Nd:YAG 1550 248 488/515 Nd:YAG 755 905 1064 532 Laser-Professionals.com  laser Lasers (A new light source). 1-Monochromatic (one color or wavelength) ‫النقاء الطٌفً أحادي اللون (لون واحد‬ (ً‫أو الطول الموج‬  Laser beam is monochromatic Laser beam is coherent  laser 2-A highly directional beam with low divergence. ‫شدة الشعاع وقلة التشتت‬  laser 3-Capable of being focused into a very small spot. ‫قادرة على أن تركز فً بقعة صغٌرة جدا‬ 4-Capable of producing short bursts of light of very high intensity (in less than a trillionth of a second). ‫قادرة على إنتاج رشقات نارٌة قصٌرة من ضوء كثافة‬ (‫عالٌة جدا (فً أقل من ترٌلٌون من الثانٌة‬ 3:Types of Lasers (A new light source). 3-1:Lasers can be described by 1-The electromagnetic spectrum is (Infrared, Visible Spectrum ,Ultraviolet) 2-The length of time the beam is active: (Continuous Wave (CW),Pulsed,Ultra-short Pulsed represented) 3:Types of Lasers (A new light source). 3-2:Types of Lasers. Solid lasers Gas lasers Semiconductor (Diode) Liquid (Dye)  4:Principles Of Laser Action The basic principle of the laser, as the name ”light amplification by stimulated emission of radiation” indicates, is based on stimulated emission from a higher level f to a lower level i (not necessarily the ground state) 4:Principles Of Laser Action. 1:Spontaneous Emission 2:Stimulated Emission 3:Amplification by Stimulated Emission. 4:Population Inversion 5:The Resonator spontaneous emission 1-when an electron is in an excited energy state, it must decay to a lower level, giving a photon of radiation. 2-The photons is emitted in a random direction and a random phase. 3-The average time is takes for the electron to decay is called the time constant for spontaneous emission, and is represented by τ. ‫ هو انطالق اشعاع من الذرة المثارة عند انتقالها من مستوى طاقة‬ ‫اعلى الى مستوى طاقة اقل بعد انتهاء فترة العمر تلقائٌا وبدون‬ ‫تدخل خارجً(الفوتون كم من الطاقة مركز لة كتلة وكمٌة حركة‬ (‫ولة طول موجى وٌتحرك بسرعة الضوء‬  stimulated emission 1-if an electron is in energy state E2, and its decay path is to E1, 2-a photon happens to pass by whose energy is approximately E2- E1, there is a probability that the passing photon will cause the electron to decay. 3-a photons is emitted at the exactly the same wavelength, in exactly the same direction, and with exactly the same phase ً‫هو انطالق اشعاع من الذرة المثارة نتٌجة اصطدمها بفوتون خارج‬ ‫لة نفس طاقة الفوتون المسبب ألثارتها لتخرج فً النهاٌة‬ ‫فوتونات لها نفس الطور واألتجاة والتردد‬ Story problems Example.(1): The visible spectrum wavelength range is: 0.4 - 0.7 [mm] (400-700 [nm]). The wavelength of the violet light is the shortest, and the wavelength of the red light is the longest. Calculate: a) What is the frequency range of the visible spectrum? b) What is the amount of the photon’s energy associated with the violet light, compared to the photon energy of the red light? The frequency of violet light: The frequency of red light:  The difference in frequencies: The energy of a violet photon: The energy of a red photon: The difference in energies between the violet photon and the red photon is: 2.15*10-19 [J].  Amplification by Stimulated Emission 1-if τ is very long. causing stimulated emission of a coherent photon 2-these two photons then interact with the next 2 atoms in line, and the results is 4 coherent photons. At the end we have 11 coherent photons, 3-identical phases and the same direction. ‫التضخٌم بواسطة االنبعاث المستحث‬ ‫ ونحن نفترض أن ‪ τ‬طوٌلة جدا‪ ،‬وذلك الحتمال االنبعاث‬ ‫المستحث هو ‪ 100‬فً المئة‪.‬والواردة (تحفٌز( الفوتون ٌتفاعل‬ ‫مع ذرة األولى‪ ،‬مما تسبب بنكوٌن فوتون متماسك‪ ،‬وهذه‬ ‫الفوتونات ‪ 2‬ثم تتفاعل مع ذرات‪ ،‬والنتائج هو ‪ 4‬فوتونات‬ ‫متماسكة‪.‬فً النهاٌة لدٌنا ‪ 11‬الفوتونات متماسك‪،‬‬ Population Inversion 1-not all of the atoms are usually in an excited state. 2-Boltzmann’s principle, states that, when a collection of atoms is at thermal equilibrium, the relative population of any two energy levels is given by: N1 = exp (-E2-E1) N2 KT Where: N2 and N1 are the populations of the upper and lower energy states T is the equilibrium temperature, K is the Boltzmann’s constant 4-5:The Resonator This is the resonator, a system of mirrors that reflects undesirable (off-axis) photons out of the system and reflects the desirable (on-axis) photons back into the excited population where they can continue to be amplified. 5:Laser Hazard Classes 1-Class 1 - “safe” (CD-ROM players/drives) 2-Class 2/2a -eye hazard (supermarket scanners) 3-Class 3a - eye hazard (laser pointers) 4-Class 3b -eye hazard (research) 5-Class 4 - eye hazard (research, manufacturing). 5:Laser Hazard Classes 6:Low Level Laser Therapy 6-1:Anti-inflammatory effects. 1-Enhance lymphatic drainage. 2-Reduces swelling 3-Reduces mucous it is after irradiation and chemotherapy 4-Reduces lymph edema. 6:Low Level Laser Therapy 6-2:Analgesic (pain reduction) effects. 1-Increases ATP production 2-Relaxation of muscle tension 4-Reduces degenerative process on central nervous system. 5-Accelerates neo-visualization. 6:Low Level Laser Therapy 6-3:Laser therapy as a healing stimulus. 1-Laser can strengthen damaged cells. 2-Using photochemical processes, laser light inserts biophotons into damaged cells. 3-The cells begin to produce energy (ATP), which improve their function, assists their division and strengthens the body's immune system. 4-The tissues are healed and pain disappears. 5- the bio-photons help the division of neighboring cells, generating new tissues and bring about healing.  ‫ وٌمكن لٌزر تقوٌة الخالٌا التالفة‪.‬باستخدام العملٌات الكٌمٌائٌة الضوئٌة‬ ‫ضوء اللٌزر‪ ،‬وتدرج الحٌوي الفوتونات إلى الخالٌا التالفة‪.‬تبدأ الخالٌا‬ ‫إلنتاج الطاقة ()‪ ،ATP‬التً من شأنها تحسٌن وظٌفتها‪ ،‬وٌساعد على‬ ‫وٌقوي تلتئم أنسجة الجسم ‪ٌ.‬قوي جهاز المناعة‪ ،‬وٌختفً األلم‪.‬وقد تجدد‬ ‫الخالٌا التالفة التً ٌكون مٌتا‪ ،‬الفوتونات الحٌوي تساعد على تقسٌم الخالٌا‬ ‫المجاورة‪ ،‬وتولٌد أنسجة جدٌدة‪ ،‬وتجلب ‪.‬أن اللٌزر منخفض الطاقة ٌمكن‬ ‫أن ٌسرع الكوالجٌن بسبب تسارع معدل النسخ مرنا من الكوالجٌن الجٌن‪.‬‬ ‫(هذا ٌقلل البروستاجالندٌن(‪.‬‬ 7:Causes Of Laser Accidents. 1-Altering beam path 2-Inserting reflective objects into beam path 3-Bypassing interlocks (particularly during alignment) 4-Accidentally turning on power supply 5-Accidental firing of laser 6-Looking back down the beam path 8-General Safety Practices. 1-Wear eyewear 2-Know where the beam is going 3-Use minimum power/energy 4-Reduce laser output with shutters/attenuators, if possible 8-General Safety Practices. 5-Keep beam path away from eye level 6-Don’t put body parts in the beam 7-Don’t wear (rings, watches). 8-Let other lab members know what you are doing 9-Read the safety of the laser manual  Solution: The frequency of violet light: The frequency of red light: The difference in frequencies: The energy of a violet photon: The energy of a red photon: The difference in energies between the violet photon and the red photon is: 2.15*10-19 [J]. Example.(2): The velocity of Red light (l0= 0.6 [mm]) in a certain medium is 1.5*108 [m/s]. What is the wavelength of this light in this material? First find the index of refraction: Using n, calculate the wavelength in the material: Conclusion: The wavelength of Red light in a material with an index of refraction of 2.0, is 0.3 [mm]  Qusetions I)Define each one of the following: :LASER )4What are the types of Lasers ? )5What are the general safety Protection from Laser beam? Thanks