eXtreme ultraviolet to soft-X-ray Photonic Integrated Circuits

Project Information

X-PIC

Grant agreement ID: 964588

DOI

10.3030/964588

Project closed

EC signature date 15 December 2020

Start date 1 April 2021

End date 30 September 2025

Funded under

• EXCELLENT SCIENCE - Future and Emerging Technologies (FET)

Total cost

€ 3 075 000,00

EU contribution

€ 3 075 000,00

Coordinated by

POLITECNICO DI MILANO
Italy

Periodic Reporting for period 2 - X-PIC (eXtreme ultraviolet to soft-X-ray Photonic Integrated Circuits)

Reporting period: 2022-04-01 to 2023-09-30

Summary of the context and overall objectives of the project

Photonics is the science of generating, exploiting and detecting photons, which are the constituents of light. We are surrounded and we continuously interact with photonic devices, that are nowadays exploited in a huge variety of applications.
A recent branch is Integrated Photonics, that aims at realizing miniaturized circuits of photonic devices generating, exchanging and exploiting photons inside or on top of a monolithic substrate.
Current technology in this field can only handle photons in the infrared, visible and near ultraviolet spectral regions, since a severe absorption in solid-state materials appear as we move towards the deep ultraviolet region.

However, developing an integrated photonic technology working with high-energy photons in the region between the extreme ultraviolet (EUV) and the soft X rays (SXR) may allow new applications with respect to the current state of the art in several fields of Science and Technology, like Chemistry, Biology, Physics and Electronics. For instance, chemical elements can be discerned by looking at their absorption in this spectral region;
SXR light can be used in high-resolution microscopy of biological specimens; EUV radiation is exploited in photolithography, which is a key step in the fabrication of microelectronic devices.
Hence EUV-SXR Integrated Photonics may provide compact and versatile solutions for applications that nowadays can be realized only in large-scale facilities or with bulky instrumentation.

The goal of the X-PIC project is indeed the development of integrated photonic circuits working with light in the spectral region between the EUV and the SXR. The main idea is to generate, manipulate and exploit EUV-SXR light in microchannels in order to minimize optical losses with respect to bulk devices. The microchannels are realized inside fused-silica substrates by a technique called Femtosecond Laser Micromachining.

The breakthrough proposed by X-PIC will be reached by developing three innovations:
- a compact and powerful laser source driving the X-PIC devices with ultrashort and intense pulses of infrared light;
- a miniaturized source of EUV-SXR light pulses driven by this laser and based on an optical process called High-order Harmonic Generation (HHG) in gases;
- a technology for the manipulation of the EUV-SXR light inside monolithic photonic circuits, in which the EUV-SXR source is integrated.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The ambitious goals of X-PIC will be reached in three steps:
1. a theoretical modelling of the EUV-SXR generation and propagation inside microchannels;
2. an experimental demonstration of the feasibility of the technology based on the results achieved in the first activity;
3. the realization of proof-of-concept devices based on the previous two activities.

During the first year of the project the X-PIC partners were involved mainly in the first activity; the second one was launched, whereas the third activity will be considered in the following years.

The first activity focused on the theoretical investigation of the generation of High-order Harmonics (HHG) driven by near-infrared intense and ultrashort laser pulses in microchannels fed with noble gases. This study requires very complex numerical calculations involving Optics, Laser-Matter interaction at high laser peak intensities and transient Fluid Dynamics inside the microstructures. The main outcomes can be summarized as follows:

1.1. the efficiency of the EUV-SXR emission by HHG inside a straight microchannel depends on the gas density profile along the channel as well as on the laser pulse propagation inside it. In particular, different profiles of the gas density along the channel correspond to different spectral shapes of the EUV-SXR. The laser propagation in the channel differs substantially from that in free space and accounts for a noticeable extension of the emission towards high photon energies.

1.2. Microchannels with corrugation of the walls or with variable diameter along the channel affect in different ways the laser propagation and can be further exploited to tailor the emitted EUV-SXR radiation.

1.3. The laser-gas interaction inside the microchannel produces shock waves reflected by the channel walls; the transient perturbation of the gas density decays on time scales faster than the delay between adjacent pulses emitted by standard laser source, however this effect should be taken into account for high-repetition-rate driving lasers.


The second activity was mainly focused on two different topics: the realization of test devices for experimental validation of the theoretical models and the design and realization of the compact laser source that will drive the X-PIC devices. The main outcomes can be summarized as follows:

2.1. Devices with different modulations of the gas density along the microchannel were realized; intense laser pulses in the near infrared, provided by an existing laser, were coupled to such devices fed with noble gases. The emitted EUV radiation was characterized by a flat-field EUV spectrometer, confirming the dependence of the emitted spectra on the gas density profile.

2.2. To exploit fruitfully the EUV-SXR radiation produced by HHG, the overlapped driving laser pulses must be rejected. Efforts were spent towards this goal by realizing suitable systems of microchannels able to reject the infrared radiation from the EUV-SXR beam by waveguiding effects. The experimental results are encouraging and improved designs of this rejection stage are underway.

2.3 The full design of the compact laser driver has been completed; the source will be based on an Optical Parametric Chirped Pulse Amplification scheme (OPCPA) able to meet all the requirements for HHG in the EUV-SXR region. The driver is now under construction.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

At the current stage, the project has already demonstrated a possible implementation of Integrated Photonics in the EUV-SRX that was not yet available. In particular, the generation and propagation of EUV radiation in engineered microstructured devices has been demonstrated.

These outcomes are the basis for the development of more complex devices; in particular the project aims at the demonstration of two applications with relevance to the semiconductor technology:
(1) a hyperspectral imaging device for retrieving at the same time shape and spectral reflectivity of nanopatterned surfaces, from which the composition of the nanopatterns can be retrieved;
(2) a tailored EUV compact source for the photolithography of integrated electronics with spatial resolution below 15 nm.

The potential impact of the project involves the semiconductor market, pharmaceutical and biological applications, the market of chemical-physical analytic devices as well as applications in Material Science.
On a wider scope, this technology may be relevant in fundamental sciences like Atomic and Molecular Physics and may inspire novel applications in optical computing and information technology.

Sketch of a X-PIC compact source of EUV radiation