Development of innovative non-linear architectures for UV fiber lasers

Abstract

This project has been performed within the Research and Development division of Bloom Lasers, located in Pessac, France. Bloom has strong expertise in developing high power ultraviolet fiber lasers. One of the key aspects that enables to obtain high ultraviolet power is to have an efficient nonlinear conversion module, which converts the Infrared into ultraviolet. The most relevant parameters that determines the conversion efficiency of the nonlinear module is the peak pulse power of the input infrared signal.

Bloom has already demonstrated efficient conversion from infrared into ultraviolet with relatively high peak power. However, a specific customer has requested for very high ultraviolet average power with very low peak power. This poses a challenge in terms of conversion efficiency. The purpose of this project has been to develop innovative and more sophisticated nonlinear architectures in order to obtain high conversion efficiency at very low input peak power.

This has required to do an in-depth study of the physics principles behind nonlinear frequency conversion in bulk crystals, and in particular frequency tripling. Nonlinear conversion experiments have been performed over the span of six months with three different laser sources. The first source is a standard and robust product, which has however different specifications compared to the final laser source. The second source is a prototype home-made laser which has more similar characteristics to the final laser source. However, this second source was initially not functioning, hence part of this work was to re-develop some aspects of its architecture. The last laser source is a
high power prototype laser. The third laser source is the final objective of the project, the first two laser sources were used for testing purposes.

The experimental results were validated with simulations done with a software called SNLO, a simulation software for nonlinear optics.

Popular Abstract

As we all know, mobile phones are essential nowadays for communication. According to an American survey conducted in 2023, people check their phones 144 times a day!
But have you ever wondered, how does your phone even work?

If you ever broke your phone, you have probably seen that there is a lot of electronics inside. In particular, the mobiles phones as most of modern electronics devices, like laptop or radios, are based on something called Printed Circuit Board (PCB). This is an electronic board which is made with very fine holes and contains really a lot of connections. All the circuits are mounted tightly on this board. These PCB to be embedded in more and more powerful devices and smaller and smaller devices need to be thinner and more dense. This allows everything to be compact, and your phone to be small enough to fit in your pockets.
Now the question becomes, how do we produce such sophisticated boards?

Unfortunately, mechanics is not good enough to do the job and its precision is limited in diameter to 100 µm (0.1 milli meters) and it is too slow in the process. A very popular answer at the current state is UV lasers that enable to drill down to <20µm (<0.02 milli meters) hole diameter and unprecedented throughput. I suppose now you are wondering what is a UV laser. We will start by explaining what is a laser, and then what is UV radiation.

You have encountered lasers before in your life, in barcode scanners at the supermarket, or in simple laser pointers. It is just light, but it is different from the light emitted by a lamp for example. It is concentrated in a small spot. Light is composed by little packages, called the photons. The photons emitted by a lamp are random and chaotic. The photons emitted by a laser are perfectly organized, because they are radiated through a quantum mechanical effect called ’stimulated emission’. This allows lasers to be very powerful. The lasers used in this work have a power up to 250 W. If your skin was exposed to such amount of power, you would scream because of the pain.

UV stands for ultraviolet, and it is a wavelength region of the electromagnetic spectrum. You cannot see it with your eyes, because it is outside of the so-called ’visible region’. But it exists, it is the wavelength emitted by the sun and it is dangerous for the skin.

Even though it is dangerous, UV has many interesting properties. For example, it can be focused to a very small spot, and it has a lot of energy due its low wavelength. This makes it a perfect candidate for making the fine holes that we need to fabricate electronics.

So this is what this study has been about: developing powerful UV lasers, which are going to be used to manufacture electronics that is used in our everyday life.

• author: Monzani, Andrea
• supervisor: Cord Arnold; Julien Didierjean
• organization: Atomic Physics; Department of Physics
• course: PHYM03 20232
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: nonlinear optics, UV laser, walk-off compensation, fiber laser, Bloom Lasers, laser development, MOPA, Second Harmonic Generation, nanosecond pulses, picosecond pulses, laser annealing, dopant wafer activation, Frequency tripling
• publication/series: Lund reports on atomic physics (LRAP)
• report number: 596
• language: English
• id: 9147745
• date added to LUP: 2024-02-05 09:00:50
• date last changed: 2024-02-05 09:00:50