Page 9 - LASERS & IPLS IN MEDICAL/AESTHETIC APPLICATIONS

Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.1
The Importance of Calibration Charts ................................................................................................................ 49
Pulse Duration .............................................................................................................................52
Q-switched Lasers............................................................................................................................................... 53 Active Q-switches versus Passive Q-switches .................................................................................................... 53 Picosecond Lasers............................................................................................................................................... 54
Power & Power Density ...............................................................................................................55
Why ‘Power Density’ is the Most Important...................................................................................................... 58 Parameter in Clinical Treatments ....................................................................................................................... 58
Spot Size......................................................................................................................................58
How does ‘power density’ vary with ‘focal drift’? ............................................................................................. 60 IPL Spot Size ........................................................................................................................................................ 62 Overlapping ........................................................................................................................................................ 63
Repetition Rate............................................................................................................................64
Pulse Trains .................................................................................................................................65
Single Pulsed Systems......................................................................................................................................... 65 Multi-pulsed Systems ......................................................................................................................................... 66
........................................................................................................................................... 68
Section 1.3 - Brief Introduction to Light Interactions in the Skin ............................................68
Introduction – “Selective Photothermolysis” ................................................................................69
Absorption .......................................................................................................................................................... 71 Reflection............................................................................................................................................................ 73 Fresnel Reflections ............................................................................................................................................. 74 Transmission....................................................................................................................................................... 74 Chromophores in the Skin .................................................................................................................................. 75 Haemoglobin ...................................................................................................................................................... 76 Melanin............................................................................................................................................................... 77 H2O - water ......................................................................................................................................................... 78 Others chromophores – Bilirubin, Keratin......................................................................................................... 78
The ‘Fitzpatrick Scale’ and Skin Colour ..........................................................................................80
Melanin Absorption and Pain .......................................................................................................81
Scattering in the Skin ...................................................................................................................81
Back-scattering ................................................................................................................................................... 84
Depth of Penetration of Light in the Skin ......................................................................................85
Effect of Wavelength .......................................................................................................................................... 85 Effect of Spot Diameter ...................................................................................................................................... 87 Clinically ‘Useful’ Penetration Depth - Definition .............................................................................................. 88 Effect of Pulsewidth............................................................................................................................................ 89
Heated volume following light energy absorption .........................................................................90
Case 1 – No scattering ........................................................................................................................................ 90 Case 2 – With scattering ..................................................................................................................................... 91 Energy Absorption versus depth ........................................................................................................................ 91
Tissue Reactions – Chemical, Thermal, Ablative & Mechanical.......................................................96 Thermal Relaxation Time .............................................................................................................97 Summary of Light-Tissue Interactions ...........................................................................................98
......................................................................................................................................... 100
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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