Lasers emit light that is monochromatic, coherent, and collimated. A laser system requires a lasing medium and uses stimulated emission to generate a laser beam. Key factors in laser-tissue interaction include wavelength, pulse duration relative to the target's thermal relaxation time, energy level, and spot size. These parameters must be optimized to destroy the target tissue while sparing surrounding areas.

1. Laser
Physics

2.  Lasers require a lasing medium
 Crystal, glass, liquid, gas or dye
 Lasers and IPLs

3. Lasers are:
Monochromatic: one wavelength or color
Coherent: all waves or photons are in
same phase
Collimated: it can be precisely directed;
straight and parallel

4. • Monochromatic
• Coherent
• Collimated
• Polychromatic
• Non-coherent
• Non-collimated light

5.  Laser light is “special”
 Orderly
 Compared to light

6. Flashlamp
F I L T E R • Multiple
Wavelengths
• Non-Collimated
• Non-coherent

7. Stimulated Emission
A photon strikes an excited atom...
And the atom emits a new
photon just like the first one.

8. Totally reflective mirror
Laser Beam
Partially Reflective Mirror
Basics of a laser
system

9. Continuous Wave
Pulsed

10.  Fluence (j/cm2)
 Joule = watt x time
 Watt – the rate of energy delivery

11. A laser pulse is a compression of
laser energy

13. Electromagnetic
Spectrum
 Made up of all
known wavelengths
 Longest is radio
waves
 Shortest is gamma-
rays
 Includes visible light

14. Radiation in Physics refers to a process in which
energy or energetic particles travel through a
medium or space.
Ionizing Radiation changes the atom

16. Visible light wavelength is between
400 and 700nm (most common)
Also noted in some texts 380nm and 750nm

18. CO2 Far Infrared 10,600nm
Er:Yag Mid Infrared 2,940nm
Nd:Yag NIR 1,064nm
Diode Lasers Visible & NIR -530 to 2,100nm*
Alexandrite Near Infrared 755nm
Ruby Deep Red 694nm
Krypton Red, Yellow, Green 647, 568, 531nm
Helium Neon Red 632nm
CuBr Yellow, Green 578, 511nm
Dye Lasers Red, Yellow, Green 632, 585, 504nm
KTP Green 532nm
Argon Blue, Green 488, 515nm
XeCl Excimer UV 308nm

19. Chromophore
The chromophore absorbs the energy.
Melanin, blood, and water

20. Laser Hair Removal:
What if there is no melanin?

23.  Nd:Yag penetrates deeper than the diode
 The diode penetrates deeper than the
alexandrite

24. Small spot
size for
superficial
targets
(7mm)
Large spot
size for
deeper
targets(18mm
)

27. For target destruction, consider:
– Wavelength
– Pulse Width or Pulse Duration
(determined by TRT)
– Energy (fluence j/cm2)
– Spot Size (where applicable)
The laser is absorbed into desired target
(Chromophore) but spares the surrounding
tissue.
Chromophore: Blood, Melanin or Water

28. Wavelength
Determined by skin color
(laser hair removal)

29. Pulse width or pulse duration:
Determined by Thermal Relaxation Time

31.  The time necessary
for the target to
cool down 50% by
 Transfer its heat to
surrounding tissue
 Related to the size
of the target and its
composition
“Small” object
Cooling
Heating
“Big” object

32.  Skin has a TRT of 5-10ms (3-10ms).
 Hair has a TRT of 40-100ms
 Pulse duration must be longer than TRT for
skin but shorter than TRT for target.

33. Chicken soup vs. Chili
Heats slower
Cools slower
Heats Fast
Cools Fast

34. Too short of a pulse duration:
- can cause a burn
Too long of a pulse duration:
- ineffective treatment

35. Pulse Width = Pulse Duration

36.  Focal length
 Focal spot
 Depth of field or waist

37.  Power Density or PD: effects on tissue
- rapid change is a change in spot size
(cutting lasers)
- slower change is a change in power
(cutting laser)
- too high PD will create burn or blister
- too low PD will make treatment
ineffective

38.  Radiant Exposure (correct term): is the
fluence in j/cm2
- more commonly referred to as Energy Density
- “dose” of light in energy per surface area

39.  Thin hair Coarse hair
 Shorter PW Longer PW
 Higher joules Lower joules