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Bio-Medical Optics Lab., Yonsei University


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  • 1. 1 Bio-Medical Optics Lab., Yonsei University 치료기기학 - 레이저치료 강의노트 III Medical Lasers Fall Semester 2004
  • 2. Bio-Medical Optics Lab., Yonsei University Absorption Spectra of Tissue Chromophores 0.0001 0.01 1 100 104 1000 104 Oxy-hemoglobin Deoxy-hemoglobin Water AbsorptionCoefficient(1/cm) Wavelength (nm) Optical Window He-Ne Ti:Sapphire Diode Nd:YAG Ho:YAG Er:YAG CO2 Melanin
  • 3. Bio-Medical Optics Lab., Yonsei University CO2 Laser Wavelength: 10,600 nm or 10.6 µm (most commonly used, mid infrared) Laser medium: CO2 gas (mixed with nitrogen and helium) Excitation: Electrical arc through the gas Characteristics Very efficient lasing (10 – 20% of electrical power is converted to the emitted power. Others normally falls into 1 – 2%) No optical fiber delivery – An articulated arm is used for delivery or hollow core fiber delivery Invisible to the naked eye  Normally used along with He-Ne laser (red) Can harm cornea seriously  Need to wear normal glass or plastic eyeware
  • 4. Bio-Medical Optics Lab., Yonsei University CO2 Laser (continued) Applications: numerous, one of the main workhorses 20W CW: Applications in vaporization of tissues Pulsed, 500W peak power, 20 – 40W average power: adjusted to appropriate level, it can be used for both vaporization and cutting of tissues without charring Skin resurfacing (pulsed, superpulsed)
  • 5. Bio-Medical Optics Lab., Yonsei University Nd:YAG Laser Wavelength: 1064 nm or 1.064 µm (most common) Laser medium: Nd ions dispersed in a crystal of yttrium-aluminum-garnet (YAG) Excitation: Lamp pumped: old technology Diode laser pumped: new technology (very durable, compact and energy efficient but expensive) Applications: numerous, one of the main workhorses 100 W CW for surgery (e.g. prostate) Coagulation and vaporization of tumors (breast cancer, liver cancer, etc) Q-switched Nd:YAG laser (10 – 30 ns pulse duration) Can cause retinal injury (goggle needed)
  • 6. Bio-Medical Optics Lab., Yonsei University Argon-ion laser Wavelength: 488 nm (blue), 514.5 nm (green) Laser medium: Argon gas at about 1 torr of pressure Excitation: Electrical Output: CW mode, power range typically in the range of 100 mW to 20W Applications Most important medical uses in ophthalmology (retinal detachment) Light sources for bioimaging Raman spectroscopy Pumping other lasers Can cause retinal injury (goggle needed)
  • 7. Bio-Medical Optics Lab., Yonsei University Diode Lasers (Semiconductor Lasers) Wavelength: From 400 nm to 1900 nm (dependent on the laser medium) Laser medium: GaN ~400 nm: 5 mW, 200 mW AlGaAs ~800 nm (near IR): 5 mW, 50 mW, 4 W InGaAs ~670 nm (red): 5 mW, 40 mW, 400 mW ~635 nm (bright red): 5 mW Excitation: Electrical Characteristics Interface between the active layer and air works as cavity mirror Extremely high efficiency in light generation Extremely small size (300 µm x 100µm x 100µm) Applications Aiming beam Low level laser therapy: pain relief, wound healing Ophthalmology
  • 8. Bio-Medical Optics Lab., Yonsei University High Power Diode Laser Diode bars containing many emitters: ~800 nm, 1 – 20W Applications Cutting of tissue, hair removal Optical pumping of Nd:YAG laser (more efficient and compact) Heat treatment of tissues (BPH treatment etc)
  • 9. Bio-Medical Optics Lab., Yonsei University Dye lasers (Liquid laser) Wavelength: Continuously tunable from 400 nm to 900 nm with the change of dye Laser medium: Fluorescent dyes dissolved in solvents Excitation Pulsed dye laser: Flash lamp, KTP laser, excimer laser CW dye laser: Ar-ion laser Applications Photodynamic therapy Dermatology Ophthalmology Vascular disorders, selective target damages of blood vessels or pigment cells
  • 10. Bio-Medical Optics Lab., Yonsei University Er:YAG and Ho:YAG lasers Er:YAG (Solid state laser, pulsed) Wavelength : 2.94 mm Excitation : Lamps or diodes Uses articulated arm or special fibers such as sapphire crystal fibers Water absorption band : Relatively low collateral damage, may be used for microsurgery Applications  Ablation of bone and tooth  Microscopic surgery Ho:YAG (Solid state laser, pulsed) Wavelength : 2.1 mm Less absorbed but can be delivered by regular fused silica fibers Strongly absorbed by water Applications  Surgical cutting of bone and soft tissues
  • 11. Bio-Medical Optics Lab., Yonsei University Excimer lasers Wavelength (gas laser, strong UV source) ArF: 193 nm KrF: 249 nm XeCl: 308 nm XeF: 351 nm Laser medium: Excited dimer gas Characteristics Strongly absorbed in tissues, especially in proteins, nucleic acids, etc… Photothermal ablation? or photochemical? (Leaves low collateral damage : cold laser) Up to 300 Hz or so Applications Ophthalmology (LASIK, LASEK), microsurgery Problems Corrosive and toxic gas, extremely expensive, dangerous UV emission (carcinogeniity problem)
  • 12. Bio-Medical Optics Lab., Yonsei University Ti:Sapphire Laser Wavelength: Tunable between 690 and 1000 nm Laser medium: Ti3+ ions in a sapphire solid host (Al2O3) Excitation: Optical, using an argon laser or a frequency-doubled Nd:YAG laser Output: CW, nanoseconds and femtoseconds pulses, power typically in hundreds of milliwatts range Applications Multiphoton microscopy Multiphoton photodynamic therapy Tissue ablation
  • 13. Bio-Medical Optics Lab., Yonsei University Free Electron Laser Lasing method Free electrons pass through an array of permanent magnets Electrons modulated emits light Wavelength (totally tunable) By changing magnet array, light from extreme UV to millimeter wavelength can be obtained continuously Characteristics Still building size Need a team of scientist to operate Applications Potential use for many types of diagnosis and therapies
  • 14. Bio-Medical Optics Lab., Yonsei University Other lasers KTP laser Frequency-doubled Nd:YAG laser using a nonlinear crystal, KTP Wavelength: 1064 nm/2 = 532 nm (green) Applications  CW KTP: Ophthalmic  Q-switched KTP (nanosecond pulses): tattoo removal, port wine stain removal Alexandrite laser Wavelength: 700 nm – 820 nm (tunable) Excitation: Flashlamps, diodes Cost effective Applications  hair removal etc.