A laser works by stimulating the emission of photons from excited atoms or molecules in a lasing medium placed within an optical cavity formed by mirrors. When photons strike excited atoms, they cause the atoms to release more photons of the same frequency, phase, and direction, producing a coherent beam of light through stimulated emission. Population inversion is needed, where more atoms are in an excited state than a ground state. Lasers have applications in medicine, communications, manufacturing, and research due to their coherence, directionality, monochromaticity, and high intensity.

1. Principles of LASER

2. laser (Light Amplification by Stimulated Emission of Radiation) is a
device that generates a highly focused, intense, and monochromatic
beam of light. The principles of laser technology are based on
quantum mechanics, and its applications span across various fields,
including communications, medicine, manufacturing, and research.

3. laser operates on the following principles:
Stimulated emission: If a photon with the same energy as the energy
difference between the excited and ground states interacts with an
excited atom, it can stimulate the atom to emit a second photon with the
same energy, phase, and direction as the first photon. This process is
called stimulated emission.

4. Population inversion: A laser medium (usually a gas, liquid, or solid)
is needed to create a population inversion, where more atoms or
molecules are in an excited energy state than in the ground state. This
is achieved through a process called "pumping," which typically
involves light or electrical energy.

5. Optical resonator: A laser cavity or optical resonator is formed by two
mirrors placed at either end of the laser medium. Photons generated by
stimulated emission travel back and forth between the mirrors, causing
more stimulated emission and amplifying the light.

6. Characteristics of Laser
Laser light has four unique characteristics that differentiate it from
ordinary light: these are
Coherence Directionality Monochromatic High intensity

7. Laser Construction
laser or laser system consists of three important components: a pump
source, laser medium and optical resonator.

8. Applications of Lasers
The most significant applications of lasers include:
1- Lasers in medicine
2- Lasers in communications
3- Lasers in industries
4- Lasers in science and technology
5- Lasers in military

9. Lasers in Medicine
1. Lasers are used for bloodless surgery.
2. Lasers are used to destroy kidney stones.
3. Lasers are used in cancer diagnosis and therapy.
4. Lasers are used for eye lens curvature corrections.
5. Lasers are used in fiber-optic endoscope to detect ulcers in the intestines.
6. The liver and lung diseases could be treated by using lasers.
7. Lasers are used to study the internal structure of microorganisms and cells.
8. Lasers are used to produce chemical reactions.
9. Lasers are used to create plasma.
10. Lasers are used to remove tumors successfully.
11. Lasers are used to remove the caries or decayed portion of the teeth.
12. Lasers are used in cosmetic treatments such as acne treatment, cellulite and
hair removal.

10. Possible risks from exposure to laser beam
Exposure to a laser beam can pose several risks depending on the wavelength,
intensity, duration of exposure, and the part of the body that is exposed. Here are
some possible risks:
1. Eye damage: The eye is the most vulnerable part of the body to laser
exposure. Even a brief exposure to a high-powered laser beam can
cause permanent eye damage or blindness. Symptoms of eye damage
include eye pain, blurred vision, and sensitivity to light.

11. The potential location of injury in the eye is directly related to the wavelength of
the laser radiation. For laser radiation entering the eye:
Near Ultraviolet Wavelengths (UVA) 315 - 400 nm
Most of the radiation is absorbed in the lens of the eye.
The effects are delayed and do not occur for many years (e.g.; cataracts).

12. Far Ultraviolet (UVB) 280 - 315 nm and (UVC) 100 - 280 nm
Most of the radiation is absorbed in the cornea.
Keratoconjunctivitis (snow blindness/welder's flash) will result if sufficiently
high doses are absorbed.
Visible (400 -760 nm) and Near Infrared (760 - 1400 nm)
Most of the radiation is transmitted to the retina.
Overexposure may cause flash blindness or retinal burns and lesions.
Far Infrared (1400 nm - 1 mm)
Most of the radiation is transmitted to the cornea.
Overexposure to these wavelengths will cause corneal burns.

13. 2. Skin burns: Lasers that emit high-energy radiation can cause skin
burns if the beam is concentrated on a small area for an extended
period of time.

14. 3. Infection: When lasers are used in surgical procedures, there is a risk of
infection if the equipment is not properly sterilized.

15. 4. Bleeding: Lasers can cause bleeding during surgical procedures, particularly
if used on areas with high blood flow.
5. Scarring: Depending on the intensity and duration of the laser treatment,
scarring may occur.
6. Radiation exposure: Certain types of lasers can produce ionizing radiation,
which can be harmful to both patients and medical professionals.
7. Damage to nearby tissue: Laser energy can sometimes affect tissue outside of
the targeted area, which can cause unintended damage.

16. The best way to protect yourself from laser light depends on the type of laser
and the power output. Here are some general guidelines:
1. Wear appropriate eye protection: Laser light can cause serious eye damage or
blindness, so it's important to wear protective eyewear specifically designed for
the type of laser you are working with.
2. Use barriers: Use barriers such as laser curtains or enclosures to prevent laser
light from escaping and potentially harming people or animals.
3. Control access: Control access to laser areas and post warning signs to
prevent accidental exposure

17. 4. Avoid reflective surfaces: Avoid reflecting laser light off of shiny or
reflective surfaces, as it can cause the laser to bounce back and potentially harm
someone.
5. Be aware of the environment: Be aware of the environment around you, as
certain materials or substances may react with laser light and cause unexpected
hazards.
6. Use laser shielding: Use laser shielding to protect sensitive equipment or
materials that could be damaged by laser light.