Recently, by chance, a team of scientists from the Swiss Federal Institute of Technology in Lausanne, Switzerland, and the Tokyo Institute of Technology, Japan, used ultrafast laser pulses from femtosecond lasers to irradiate atoms in tellurite glass, discovering mention of an amazing secret.
Atoms of tellurite glass irradiated by the femtosecond laser reorganized, allowing the scientists to discover a way to turn tellurite glass into semiconductor materials. Why is this discovery amazing? The main reason is that when semiconductor materials are exposed to sunlight, they generate electricity, which means that in the future it will be possible to transform windows in people's daily lives into single-material light-harvesting and sensing devices that undoubtedly hold great potential.
The experimental team from the Swiss Federal Institute of Technology in Lausanne, Switzerland, stumbled upon the formation of semiconducting tellurium nanocrystalline phases on the surface of glass when they were trying to understand the self-organization process in glass, which triggered their idea of exploring possible photoconducting properties and light energy harvesting devices related to them, among other things.
The researchers made the discovery by modifying the glass with the help of tellurite glass produced by colleagues at Tokyo Institute of Technology and a femtosecond laser and analyzing the effects.
Transforming tellurite glass into a transparent light energy collector
After etching a simple pattern of lines on the surface of 1cm diameter tellurite glass, this led to the discovery that the glass was capable of generating electrical currents that lasted for months when exposed to the ultraviolet and visible spectrums.
So how does a femtosecond laser do this? It starts with the principle of femtosecond laser processing.
Femtosecond laser processing is an advanced processing technology based on a multi-photon nonlinear absorption and ionization mechanism. When a femtosecond light pulse is applied to the surface of a material or to the interior of a transparent material, the area of action of the light pulse is extremely small due to the extremely short duration of the light pulse (femtosecond level), while the light intensity is extremely high. In this case, the energy of the laser pulse does not have time to travel around the point of action, so that the action or processing of the light pulse is over in a very short period of time.
This extremely short time of action allows the energy of the laser pulse to be absorbed by the material mainly through a nonlinear absorption process, instead of the conventional linear absorption of photon energy. Due to the non-linear absorption, the energy of the laser pulse is not accumulated by the material in the form of heat and therefore the heat generated is almost negligible.
Since very little heat is generated, there is virtually no thermal damage to the material being processed, which is a major advantage of femtosecond laser processing. This type of processing avoids the heat transfer effect, resulting in much higher precision and results.
It is precisely because femtosecond laser processing triggers a localized ionization phenomenon triggered by the multiphoton absorption process, which is further amplified by subsequent cascading events such as avalanche and/or tunneling ionization.
Simply put, when the internal structure of a material is disrupted and it is in a state, the conditions have been created for recombinant material phases that are more stable compared to their initially substable (glassy or non-glassy) counterparts.
In the case of tellurite glass, as its structure changes upon exposure to a femtosecond laser, seeds consisting of clusters of tellurium atoms form and eventually grow into tellurite nanocrystals as the glass phase breaks down.
Initially the material does not conduct electricity and is unable to collect photons, but once transformed with a femtosecond laser, its local behavior is completely different.
What is also amazing is that this work does not require a variety of materials to fabricate, but simply uses the laser to locally alter the material so that the altered region behaves differently from the original material. The low cost and simplicity of using a laser makes it scalable to any type/size of substrate, simply by scanning the laser beam over the surface of the material.
There are still issues that need to be understood, and there is still a process to be followed to improve the performance of the device and take the concept from experimental to industrial implementation.
One of the big challenges is how to ensure that the improved area that absorbs light is also an area that is invisible to the naked eye, so that the window maintains its functionality, while allowing people to see clearly through the glass to the outside and keeping it aesthetically pleasing.
However, at this stage some potential photonics applications that require work such as detecting and quantifying the presence of light at specific wavelengths or spectral ranges have been able to benefit from this.
