Laser Technology: Principles, Functionality and Uses

Laser Technology Master Class Questions

• What is a laser, specifically focusing on the laser principle?
• How do lasers function?
• Critical process parameters are key to laser technology.
• What types of lasers are used in modern day industry?
• What are the uses of lasers?
• How accurate can laser cuts be?
• Which materials can be laser cut, and what is the maximum thickness?
• Is laser light dangerous?
• Can stainless steel be laser welded?

About Peter Plapper

• Possesses practical experience in system planning, optimisation, and laser system demounting
• Has worked in the US and Europe
• Heads the Laser Technology Competence Center
• Completed 11 PhD supervisions, where half related to lasers
• Has 40+ publications related to laser welding
• Reviewer of journals and EU research

About Mahdi AMNE ELAHI

• Holds a Bachelor's and Master’s degree in material science and engineering
• Worked as a Process Engineer and Head of QC and Lab
• Was a doctoral researcher with an FNR industrial fellowship grant
• Was a post-doctoral researcher
• Is an Advanced product/process expert at the Glass Competence Center

Course Structure

• The course covers a wide range of topics related to laser technology and its applications
• Introduction, Fundamentals, Beam Sources, Laser matter interaction, Beam guidance, safety.
• Quality, process defects, hybrid NC, Hardening and softening, cutting and drilling ablating.
• Welding, Brazing, welding of dissimilar materials, welding of Polymers, Welding of materials, Summary.

Learning Outcomes/Acquired Competencies

• Understanding the different laser types, their creation, and propagation
• Assessing appropriate laser beam sources for various applications
• Suggesting concepts for new laser applications
• Distinguishing parameters that affect laser beam energy absorption and knowing critical process parameters
• Describing industrial applications for lasers
• Understanding current research results and scientific methods

Introduction to Laser Technology (Lecture 1)

• The overall scope of the laser technology course
• Distinguishes laser light from ordinary light
• Explores key components that make up a laser system
• Covers various technological and commercial aspects
• Presents a concise learning summary

Difference Between Laser light and “Normal” Light

• Laser light is monochromatic, parallel, coherent, and has high energy density
• "white" light is polychromatic, divergent, with different phases, and low intensity
• Conventional sources emit white light in all directions at a low energy density
• Lasers emit single-wavelength, coherent, parallel radiation, achieving high intensity
• Temporal coherence allows lasers to produce a narrow light spectrum
• Spatial coherence allows focus, and enables long distance travel without spread

Manufacturing Technologies with Lasers

• Lasers are applicable to almost all manufacturing technologies
• Laser based manufacturing covers primary shaping, forming, separating, joining, coating and material properties changes
• Specific processes include Stereo-lithography, laser bending, cutting, welding, coating, hardening, laser sintering, ablation, brazing, additive manufacturing, and annealing

Main Parameters of a Laser System

• Laser systems are characterized by wavelength, power, pulse duration, energy density and pulse repetition rate
• Further parameters include coherence length, polarization, focal position, beam diameter, and divergence and energy density

Laser Material Processing

• Laser material processing involves distinct combinations of laser intensities and interaction times
• Laser intensities and interaction times create texturing, ablation, plasma, welding, cutting, melting, heating, and hardening

Temporal Coherence

• Describes the phase consistency of a wave across time
• Relates to the beam’s monochromaticity, meaning its single-wavelength properties
• High temporal coherence enables lasers to achieve very narrow spectral width

Spatial Coherence

• Describes the phase consistency of a wave across space
• Helps focus beams over long distances and produce sharp interference patterns
• Makes laser beams highly directional and capable of maintaining intensity over distance

Introduction Learning Points

• Specialty of laser light must be understood, and laser/normal light must be differentiated
• Should be able to list main parameters of a laser system, and allocate manufacturing processes according to power density, and exposure time
• It is important to know which energy density is required for welding
• Increasing welding speed effects welding depth
• You must know the top three manufacturing technologies for laser

Laser Creation Content

• Atoms, waves, light, and electromagnetic Radiation
• Polarized light
• LASER: Light Amplification by Stimulated Emission of Radiation
• Laser characteristics
• difference to "normal" light
• Learning control

Atomes and light - summary

• Conventional light like the sun emit light across all wavelengths
• Laser beams emit light across a narrow wavelength, and are monochromatic
• Laser light is coherent, with all light waves in phase
• Laser beams emit parallel laser beams
• Laser beams precisely guided, suited for production with megawatt light

Light as electromagnetic wave

• Humans can detect light in the 400 to 800 nm range (790-380 THz)
• Nearby spectral ranges like UV and infrared are also called light
• Electromagnetic spectrum include gamma and X-ray range, and microwaves and radio wave
• Higher frequency and energy correlate with shorter wavelengths

Light as electromagnetic wave

• Discharging gas emits photons of that spectrum
• A helium gas discharge has isolated and narrow emission lines
• Atoms in the gas discharge release absorbed energy in defined portions
• Light passing through small openings bend and spread, this is Diffraction
• Light waves overlap to make constructive or destructive pattern. this is Interference
• Wavelengths are diffracted at differing angles that means you can separate white light via diffraction
• Diffraction is governed by dsine=mλ
• d - spacing between slits
• 𝜃- angle
• m - diffraction order
• λ - Wavelength of light

Light as electromagnetic wave

• Light is electromagnetic represented transversally oscillating with fields E and H at frequency f
• Wavelength and frequency can be linked, c=λ*f. This is the propagation speed.
• Propagation speed in a vacuum is c=2.998*10**8 m/s. Reciprocal wavelength is designated the wavenumber.
• Fields can oscillate perpendicular or linear to radiation. Transverse waves may have unique polarizations in both x and y directions.

Polarized light

• Light waves are normally in multiple planes, but polarization light waves vibrate on a single plane
• Light becomes polarized through reflection (glass or water), polarizing filters, or scattering
• Polarization reduces glare, improves photography contrast, and enhances LCDs

Light as electromagnetic wave

• Superposition of such electromagnetic waves is possible, each superposition can have different phase
• Adding orthogonal waves is possible when a wave with a linear polarization rotates at 45° from the x to the y axis
• Breaking any plane wave in a linear polarization is also possible, as is separation into components

Atoms and light – Laser

• Laser light is monochromatic and coherent
• "White" light is polychromatic and divergent
• A conventional light emits a lot of visible wavelengths
• A laser beam is monochromatic with a narrow wavelength, example, 1064nm.
• Light is coherent and all wavelengths are the the same phase
• An optical resonator emits parallel laser beams
• Lasers are suited for production and travel long distances with high energy up to MW/cm²

Laser characteristics from Atoms and Light

• There must be radiated term caused by energy of exitation releasing

• Photons are coherant and parallel

• Atomic systems can exist in some states

• Each orbit occupies definite excitation levels. A transition between states absorption/emission with h*V, h - Planck Constant

• lower (ground) state needs photons frequency

• Einstein process for how atoms interaction with field

1. spontaneous emission
2. absorption
3. stimulated emission

• The conditions of population is where particles or levels in energy
• Main Laser materials, gas CO2, Nd, YAG, Yb, Er, and crystals

Atoms and light 2

• Population: When inverting from stimulated emission, inversion is more beneficial than emission
• The state has the largest electron distribution
• Levels: Many levels of photons
• 3 (Ruby)
• 4 (Nd:YAG)
• Population inversion to 2 energy levels
• Electrons pump to high level EO and E2 with absorption, with short life cycle
• For laser net with energy level EO / E1 emission and radiation exists

Laser emission

• There is also "monochromatic" with emission
• Bandwith to energy of beam has range of levels, some stable
• Inactive material = core laser
• Media can exist with gaseous solid and liquid form

Wave Coherence

• Two waves can have different path differences, these are called coherent -Randoms waves are incoherent _ stimulated emission has consistent wave form -Comparison with lights with similar light length, allows the length gauging through the wave

Stimulated emission in Laser material

• Requires pump source of energy
• Needs amplifiers
• Positioning between parallel mirrors provides radiation
• Photons have to stimulate emission to lead to amplification
• Beam distance needs integral multiples to maintain phase
• Use with mirrors to create coherent and monochromatic light

Requirements for operational Laser

• Light amplification requires Laser active material
• Supply the correct phase, some wave part must be returned
• Pumping must continue constantly

Laser Materials in Laser Beam

• The mirror is semi transmissive shown to model for laser beam
• It's more convenient shown, we have a plane on the wave for a decent model
• Creates intensity throughout rectangular sections
• Change to intensity behind the rectangular piece diffraction
• Every point and source emit spheical waves, to add paths you need the waves to add up on a half-space behind cover
• maximums is achieved on an axis of symmetry with amplitudes of waves
• This is spatial coherence
• Interference is the feature for many coherant rays
• incoherent rays cannot interfere

Beam Resonator

• Mirrors have non perfect reflection at R100

Laser Resonator

• A plane electromagnetic is an example of of a vacuum that absorbs Y2
• Intensity reduces by the length X in the medium and remains the same if it's constant
• when a beam transfer cavity P then the beam reduces exponentially using L and alpha
• after a mirror reflects, the portion of it leaves

Lasers - Transversal Modes

• Light beam must make several revolutions to start inside resonator
• Stands for Transverse Electromagnetic Mode (TEM)
• TEMoo is fundamental with intensity on peak
• Has a Gaussian intensity distribution and is the lowest order transverse mode
• Higher the intensity are labelled by m, which is intensity that has a horizontal number
• TEM 10 two peaks, Bright spots
• TEM01 more intensity but vertical and top,bright spots
• TEM 11 like a grid of 4 spots
• The complex mode's have intricate patterns and peaks

Transversal Modes

• Geometry of design is of great importance for emitted lasers.
• The power is what delivers stationary beams to cross the electromagnetic
• Dimensions of resonatour is radius
• Vibration modes result in intensity distribution
• Indices, index number of zero points of strength / inside resonator has one point
• There exist transverse electricity modes with the ring mode

Laser Beam

• Real lasers have beam power for the gas and are at high powers is less high
• Laser Intensity must be equal to distance and normal distribution

Beam Mirrors

• mirrors must con-cave to reflect laser
• Radius must be small in lens