Application of High Power Lasers in Engineering

Question 1

Laser

Answer 1

Coherent: all EM waves are in phase
Directional: straight line
Monochrome: can choose the frequency to get maximum absorption from the material
Temporal control: can switch on and off
High energy deposition

Question 2

Laser Physics

Answer 2

Once a photon has been absorbed, it will excite and energy level. This will then be emitted randomly.

If you have an exited energy state, and then stimulate it this will stimulate the emission of the first photon and the second. These will both be in phase.

Increase the energy of the ground state atoms. These will then start spontaneously emitting photons which will stimulate other atoms to release photons. This will then continue to build up.

Question 3

Type of Lasers

Answer 3

Diode:
Can stack them up to increase
Not coherent across layers

Eximer:
The separation produces a burst of light
Use toxic gases
Used to produce inkjet nozzles

Question 4

Beam Quality

Answer 4

The best beam quality has a gaussian distribution, with the centre being the highest intensity and this dropping off at the edges

BPP is a measure of beam quality

The better beam quality has a better processing capability

Question 5

Fibre Laser Construction

Answer 5

Gain medium: The gain medium in a fiber laser is typically an optical fiber doped with rare-earth elements, such as erbium, ytterbium, or neodymium. The doping creates the necessary energy levels for laser amplification.

Pump source: A pump source, often a diode laser, is used to energize the gain medium. The pump energy is absorbed by the dopant ions in the fiber, raising them to higher energy states.

Fiber Bragg Grating (FBG):
An FBG is a periodic variation in the refractive index of the optical fiber. It acts as a wavelength-specific mirror, allowing the laser to operate at a specific wavelength determined by the FBG characteristics.

Resonator Cavity:
The fiber laser typically contains a resonator cavity formed by the fiber ends and mirrors. This cavity allows for the amplification and feedback necessary for laser operation.

Output Coupler:
One of the fiber ends has a partially reflective coating, serving as an output coupler. It allows a portion of the laser light to exit the cavity, creating the laser beam.

Combining Fiber Lasers:
Fiber Laser Arrays:
Multiple fiber lasers can be combined by arranging them in an array. Each fiber laser in the array operates independently, and their outputs can be combined to achieve higher overall power.

Question 6

Laser Cutting

Answer 6

While conventional forms of cutting worked well, there was a need for a safer, more efficient and more reliable process that could rise in line with the growing demand for manufacturing and production
Non-contact process
This means that the beam used doesn’t physically touch the material that it is working with, instead causing the melting and cutting process through heat. This means that damage to the material is minimised and costly repair and maintenance schedules for moving parts that contact the work surface can be avoided.
Low power consumption
This is an important advantage in a world that is looking to work smarter, not harder by driving up production while lowering costs.
A cutting machine will only use around 10kW of power, whereas other cutting processes use more around the 50kW mark.
A safer method
With the need for increased production comes the need for increased safety too. Laser cutting is a much safer method than other cutting processes as the beam that is being used is sealed a tight light box.
Can work with many different materials
Whether it’s metal, diamonds, plastics, wood, glass or many other materials, a Laser will have no problem cutting it down in size or helping to create complex and intricate shapes.
Incredible precision – 10s of µm.
The highly accurate and precise nature of cutting is one of the greatest benefits that lasers have brought. It allows for highly accurate cuts that leave a clean cut and a smooth finish. This has helped products, components and devices to become much smaller, and vastly reduces the amount of material wastage that has been seen in the past.
Incredible speeds – up to m/s
This depends on thickness ranging from m/min for thick plates (50mm) to 2m/s for thin foils (100 µm)
Laser welding
Laser cladding: DED

Question 7

Ultra Fast

Answer 7

There is no transfer of energy or shockwaves to the surrounding material

Nature’s Fastest Event

Faster than extra-atomic events

Applications: nanoimprint tools, MEMs, fibre sensors, large area displays, microfluidics, graphene

Question 8

Extreme Light Sources

Answer 8

The 2018 Nobel Prize in Physics was awarded to Professors Donna Strickland and Gerard Mourou for their development of chirped pulse amplification (CPA), a technique that enabled the creation of extreme light sources. CPA has paved the way for groundbreaking lasers with extraordinary power and short durations. Notable examples include the Orion laser facility, capable of delivering 200 joules in less than 500 femtoseconds at 400 terawatts, and the Shanghai Superintense Ultrafast Laser Facility (SULF) with an impressive 5.3 million billion watts, or petawatts (PW) of power. These extreme light sources have applications in diverse fields, including industrial laser materials processing.

Question 9

Government Applications

Answer 9

Avenger- RPG killer utilisers lasers to shoot down lasers

Starshot: speeding to a star using laser power