Fundamentals of lasers Flashcards
What is a laser?
A device that emits light (EM radiation) through a process of optical amplification based on the simulated emission of radiation.
What are the three useful properties of lasers?
- It is monochromatic. A single wavelength of light. 2. Coherent. All the waves are in phase. 3. All the waves go in a single direction.
What is stimulated absorption?
When an electron absorbs a photon of light and goes to a high energy level.
What is spontaneous emission?
When an electron falls in energy levels and emits a photon of light in the process. It does this on its own without a trigger.
What is stimulated emission?
When a photon of light interacts with a high energy electron. The electron falls in energy and emits a photon identical to the first photon, creating a pair. The two photons are identical.
What is population inversion?
When there are more electrons in the high metastable state than in the ground state.
What is the trend for lasers?
Shorter wavelengths and shorter durations. Materials absorb shorter wavelengths better.
How could you produce shorter wavelengths of light?
Use 2nd or 3rd harmonics of light. This uses more power for less light though.
What are some of the factors affecting laser material interactions?
What is Absorptivity?
The fraction of incedent radiation absorbed by the material.
What is the beer lambert law?
What is the rough reflectivity of metals?
80-90%
What is a rough graph descriding the absorptivity of different materials?
What is the equation for beam divergence?
What are diffraction limited beams?
- beams with a minimum possible beam divergence for a given wavelength
What is brightness?
What are affecting the absoption of metals?
incident angle
surface roughness (⇧ with roughness ⇧)
surface temperature (⇧ with temperature ⇧)
sufficiently high laser intensity (0.1 – 1MW)
What are some of the different laser beam profiles?
What is the rayleigh length?
What is the equation for total angular spread?
Zr is the rayleigh length
What is the M2 factor?
a common measure of propagation quality of a laser beam. For an ideal beam it is 1.
Higher M2 values might be wanted for welding metal.
What is a diffraction limited beam?
An ideal beam with the minimum possible divergence for a given wavelength.
What are gaussian beams?
Gaussian beams are selfconsistent and their amplitude profiles (shapes) are only scaled in the transverse direction.
What is the equation for fluence?
What is the ablation threshold?
What is laser ablation?
a collective phenomenon involving the excitation of a large number of atomic sites accompanied by the formation of a dense plume of gas (plasma, ionized vaporized material) resulting in the removal of material from a surface
What are ablation regions?
laser-material interactions (sublimation regime) with a tight temporal control to contain excitation energy to the absorption region with minimised thermal damage and melting.
What are the different prefixes for small durations of time?
Milli 10-3
Micro 10-6
Nano 10-9
Pico 10-12
Femto 10-15
What are some of the material dependent time constants?
How long are long and short laser pulses?
Long pulses are of the ms or ns duration.
Short pulses are less than this.
