1. ECEN 2010 April 28,2014
Frank Barnes

2. Laser Characteristics
1. Coherence in time and space by comparison to ordinary light sources.
2. The atoms radiate dominantly by induced emission in synchronism and in the same direction.
3. This lead to very high power densities, narrow linewidths and the ability to focus into small spot sizes.

3. Laser Characteristics
4. The high power and high power densities mean that reflections of even a few percent can lead to eye damage.
5. Examples 105 W/cm2 of a glass can lead to peak powers of KW/cm2 that will lead to eye damage.
6. Q switched Nd YAG lasers at λ= 1.06µm off an optical component are a common source of problems.

4. Typical Accidents
1 These often occur in the IR and UV where you do not see the beam

5. Laser Safety 1. The eye is the most sensitive part of the body.
2. Absorption leads to
A. Heating and Thermal Chemistry
B. Photochemistry
3. Important Parameters
A. Radiance of the source
B. Wavelength
C. Characteristic of the tissue
4. Direct Beam and Scattered Light.

6. Maximum Permissible Exposure
MPE set by ANSI
1 Class I Lasers are safe and will not produce damage under normal use
2. Class II Low power only in the visible. Safe with blinking.
3. Class III Not safe for even brief viewing.
4. Class IV These are hazardous even to the skin

8. Absorption Bands 1. Strong by H2O for λ>2.5 μm
2. Thermal Damage for ΔT> 10o C to 50o C to tissue
3. Near IR mostly thermal damage for exposures greater than 10 sec.
4. Visible in the blue < 400 nm both photochemical and thermal chemical.
5. UV mostly photochemical

9. The Eye 1

10. Laser Damage
1. Q switched and mode locked lasers can generate acoustic waves due to thermal expansion. Δt< 10-7 sec and high peak powers.
2. The eye focus visible light from about 17mm by about 105 or down to about 0.2μm for λ/2= 250nm.

11. MPE in the IR + Visible 1

12. Absorption Coefficients.1

13. MPE Cornea Mid to Far IR

14. UV Absorption of Ocular Media

15. UVA MPE

16. MPE for Some Common Lasers

17. Effects at weak IR exposures on Biological Systems
1. Experimental data show changes in membrane potentials, ΔΨ, reactive oxygen species, Ca+2 , NO* , pHi fission-fusion homeostasis of mitochondria.
2. cytochrome c oxidase is considered as the photo acceptor
3. Reference Mitochondrial Signaling in Mammalian Cells Activated by Red and Near-IR Radiation Tiina I. Karu* Photochemistry and Photobiology, 2008, 84: 1091–1099

18. Question of Possible IR signals from mitochondria to the nucleus and reverse
Nowadays it is thought that this kind of treatment is based on the ability of light to alter cell metabolism as a result of its being absorbed by mitochondria and cytochrome c oxidase in particular.
The existence of a cellular signaling pathway—mitochondria cytoplasm (plasma membrane cytoplasm) nucleus—was proposed as far back as 1988

19. Increases in DNA and RNA
The action spectra for increase in DNA and RNA synthesis rate can be recorded when cultured cells are irradiated with radiation in
the 300–860 nm region.
It was shown by Schroeder et al. (that IR-A radiation (760–1440 nm), in contrast to UV, elicits a retrograde signaling (mitochondria to nucleus) response in normal human skin fibroblasts.

20. Measured Changes
1.The experimental data demonstrate that this signaling can be mediated via ΔΨ, generation of ROS, changes in Ca2+ flow, NO• binding to cytochrome c oxidase,
2. Experiments also changes in cell growth rates with exposures to different wave lengths 620–680 and 760–895 nm and not other .
Maxima near 620, 680, 760, and 825 nm) may be related to the cytochrome c oxidase

21. Figure 1 presents a putative schematic of mitochondrial retrograde signaling activated with irradiation in visible and IR-A regions.

22. Changes in Genes
of the cell

23. Summary
1. We are seeing many of the same kinds of changes with IR and visible light that we are seeing at RF , ELF and static magnetic fields.
2. Safety standards are set first for high level exposures and over time you see changes at lower intensities and longer periods of time.