Direct Laser Recording

Direct laser writing (direct laser writing) in the volume of various optical media has proven itself as a flexible and effective technology for forming waveguides and waveguide circuits in a three-dimensional format. This method allows structure the refractive index of the medium with micron and submicron resolution.^[1]

2022: ITMO studied direct laser recording of nanosets

On May 6, 2022, researchers at the Faculty of Nanoelectronics at ITMO University reported that, together with colleagues from FIAN, RKhTU named after D. I. Mendeleev and NIU MEPhI, they conducted a study in which they found out that nanosets have high spectral selectivity. Their layers can be used as filters for specific wavelengths, and up to six layers can be recorded on one glass plate. Thanks to this technology, scientists have implemented dispersion birefringent filters, which can be used for various applications: for example, to create biochemical sensors for diagnosing the flow of bacteria or augmented and virtual reality displays with a color image.

It was reported that for two years, scientists have been modeling, developing and testing integral optical elements to build a waveguide holographic periscope - a key element of augmented and virtual reality glasses of the next generation. Virtual reality helmets usually limit users' visibility - and smart glasses complement visual space and output additional information about objects and the environment.

To create such a device, you need to solve several problems, for example, how to transfer an image to a person through the glass of glasses and make the picture color. For this, researchers at ITMO laser-plasma method of glass processing (LIMP). It allows you to create laser beam converters that are actively used in the project to apply structures with a submicron period. The direct laser recording method then produced volumetric periodic structures within the glass with a modified refractive index. More details here.

2020: Russian chemists "savvy" laser

On December 22, 2020, it became known that scientists from RCTU and IOF RAS studied the role of plastic deformations in direct laser recording, and how they can be used in optical chips for quantum computers.

Femtosecond laser - using a similar installation, laser recording was carried out in experiments. Image: MIPT/Flickr, Creative Commons

As explained, Russian scientists from RKhTU and IOF RAS investigated what happens when laser radiation affects one optical crystal - yttrium-aluminum grenade, and showed that plastic deformations play a key role in direct laser recording. By means of direct laser recording, optical microcircuits in the volume of glasses and crystals can be obtained, in order, for example, to create hundreds of microlasers on a small piece of material. The work is published in the journal Scientific Reports. The study is supported by the Russian Scientific Foundation.

Since time immemorial, humanity has used the possibilities of plastic deformation, for example, when forging metal. However, in our study, we may for the first time describe plastic deformation initiated not on the surface of the crystal, as usually occurs at mechanical pressure on the sample, but inside it. commented by Andrey Ohrimchuk, an employee of the Russian Art Theater and the IOF RAS, one of the authors of the work

If focused and intense laser radiation is directed at glasses or crystals, then different optical structures can be drawn directly inside them. This method is called direct laser recording. Often, it uses femtosecond lasers that generate small-duration pulses of 10-13 seconds. Their intensity is so large that if the material is moved along a rigidly focused femtosecond laser beam, the chemical structure and, as a result, the refractive index will change in a certain area inside it. So you can make an optical waveguide - this is an analogue of wires on electric microcircuits, only optical signals, not electrons, propagate through the waveguide.

For a good waveguide, it is necessary that the refractive index varies uniformly along its entire length - so the radiation will move along it, like a pipe, and not "flow out" anywhere. But in order to accurately control direct laser recording, you need to understand well what physicochemical processes are behind it - what exactly happens to the material when it is irradiated with femtosecond laser pulses. However, if the reasons for the change in refractive index when writing in glasses are already clear to scientists, then similar phenomena in crystals have been studied much worse, although they are more suitable for creating optical waveguides.

Our proposed mechanism can be relevant not only for yttrium-aluminum garnet, but also for other crystals, which will contribute to the study of direct femtosecond laser recording. Therefore, our results can play an important role in the development of approaches for creating micro- and nanostructures in crystals that are in demand in obtaining compact laser sources for industry and medicine, optical chips for quantum computers, as well as recording information with unlimited shelf life. noted Andrey Ohrimchuk

In the work, scientists focused the laser beam inside the material and gradually moved it, changing the speed of focus movement and the energy of the laser pulse from experiment to experiment. The researchers then looked at how the refractive index of the crystal changes from these actions. It turned out that it is significantly reduced at the places of plastic deformations caused by laser radiation, and the intensity of this effect is determined by the formation and sliding of dislocations - linear defects of the crystal lattice.

The researchers identified three variants of plastic deformations. In the first dislocation, they slide freely in the volume of material, in the second they become so many that they interfere with each other's movement, and in the third dislocation concentration is intermediate and they form regular microstructures in the crystal. The plastic deformation scenario and, ultimately, the refractive index of the laser-modified section of the grenade is determined primarily by the number of laser pulses hitting one point - that is, set by the laser recording mode. Thus, scientists have established how, by changing the laser recording mode in an yttrium-aluminum grenade, it is possible to control the structure of the optical waveguide created in its volume.

This can be useful for creating waveguide microlasers. A conventional laser is a complex system of optical elements, the heart of which is the so-called active medium - an optical crystal, measuring from several centimeters, in which radiation is generated and emitted when excited. But instead of combining complex elements, you can create a laser - or even hundreds of microlasers - by "drawing" its chip on a piece of optical crystal. Previously, scientists did this using electronic lithography or other expensive and complex methods, but recently they have been using direct laser recording - it is enough to correctly adjust the recording parameters and the necessary scheme can be "drawn" in a few minutes.

See also

• Laser printing
• Laser printers
• Laser equipment (lasers) (Russian market)

Notes