Leitmotiv

Our research is focused on novel means and principles for manufacturing and designing integrated microscale components that combine multiple functionalities, such as optical, mechanical, electrical and fluidics functions among others. In particular, we have special interest for means of manufacturing three dimensional multiscale integrated systems.

The work articulates itself around four main topics:

  • Tailoring material properties at the micro-/nano- scale, for instance through laser induced polymorphic phase generations.
  • Multiscale manufacturing and force-field shaping of micro-objects, for instance using the physics of phase transformation, surface tensions or other generic physical phenomena to generate shapes, not achievable otherwise.
  • Novel modular generic platforms for assembly-less multifunctional system integration, like for instance finding new concepts for contact-less sub-nanometer positioning, seamless integration of three dimensional metallic structures with optical devices, or new principles for monolithic optical benches with nanometer positioning accuracy.
  • Self-organization process in laser-matter interaction processes

Below, you will find a few illustrations of some of our ongoing efforts.

Using laser to generate polymorphic phases

Ultrafast lasers generate high pressure conditions that open the possibility to generate polymorphic phases of a same material.

These polymorphic phases can for instance have higher or lower density, different thermal properties, or non-linear optical responses.

Finding new ways of generating these phases, in particular through direct-writing processes, would open up a broad number of design opportunities for three dimensional direct write systems.

The picture illustrates a scanning electron images (SEM) of a crater formed after exposure of a fused silica glass substrates using novel laser beam shaping techniques (spatio-temporal focusing).

Tailoring stress states in transparent materials

Stress plays an essential role at the micro‐scale.

While it can be detrimental if not controlled, it can also be used for instance to create new optical components, like polarization devices, to induce a localized  controlled anisotropy in a material or simply, for repositioning elements with sub-nanometer accuracy.

We investigate how ultrafast lasers can be used for locally tailoring stress‐states and to distribute it in a controlled manner, in three dimensions. Applications are foreseen in integrated optical polarization devices as well as for fine contact-less positioning of micro-objects.

The picture illustrates photoelastic measurements (left) [ and its numerical simulation (right) ] of a tube written in the bulk of a glass substrate. The tube was written using femtosecond laser in the bulk of a glass substrate. The stress anisotropy comes from the self-organized nano-structures introduced by the laser. 

  • B. McMillen, C. Athanasiou, and Y. Bellouard, “Femtosecond laser direct-write waveplates based on stress-induced birefringence,” Optics Express 24, 27239 (2016).
  • Y. Bellouard, A. Champion, B. McMillen, S. Mukherjee, R. R. Thomson, C. Pépin, P. Gillet, and Y. Cheng, “Stress-state manipulation in fused silica via femtosecond laser irradiation,” Optica 3, 1285 (2016).
  • B. McMillen and Y. Bellouard, “On the anisotropy of stress-distribution induced in glasses and crystals by non-ablative femtosecond laser exposure,” Opt. Express 23, 86–100 (2015).
  • A. Champion, M. Beresna, P. Kazansky, and Y. Bellouard, “Stress distribution around femtosecond laser affected zones: effect of nanogratings orientation,” Opt. Express 21, 24942–24951 (2013).

Mechanical properties of glass at the micro-/nano- scales

Fused silica has very interesting mechanical properties. It is a perfect elastic material with nearly zero-damping. The ultimate stress the material can withstand is dictated by fracture mechanics and by the presence of surface flaws.

If properly processed, it can withstand very high stress, significantly higher than steel. Strength of several GPa have reported for fibers. We have demonstrated strength well above 2 GPa for non trivial shapes such as flexures.

This property is particularly intereting for micro‐scale mechanism, like flexures. The material being transparent, stress distribution can also be directly observed using photoelasticity.

We investigate the behavior of silica material at the micro-/nano- scale and how the material behaves under high stress.

The picture shows a photoelastic measurement on a micro-scale beam (width is about 8 microns) subjected to a perfect tensile stress of 2.4 GPa.

  • C.-E. Athanasiou and Y. Bellouard, “A Monolithic Micro-Tensile Tester for Investigating Silicon Dioxide Polymorph Micromechanics, Fabricated and Operated Using a Femtosecond Laser,” Micromachines 6, 1365–1386 (2015).
  • Y. Bellouard, “On the bending strength of fused silica flexures fabricated by ultrafast lasers [Invited],” Opt. Mater. Express 1, 816–831 (2011).

Investigating self-organization mechanisms

Remarkably, intriguing self-organization phenomena may take place when materails are exposed to intense laser beam, inducing high electrical field conditions.

These periodic structures can take various forms (straight nanoplanes, trail of micro-bubbles, curved shells, etc.) depending on the laser exposure conditions.

These self-organized patterns form naturally for instance during continuous scanning. This is particularly interesting for applications requiring highly periodic elements over large surfaces or lengths.

The picture is a scanning electron microscope image of a highly periodic semi-cylindrical patterns formed during continuous scanning at high velocity of a silica surface and after a brief etching step. 

  • E. O. Kissi and Y. Bellouard, “Self-organized nanostructures forming under high-repetition rate femtosecond laser bulk-heating of fused silica,” Optics Express 26, 14024 (2018).
  • C.-E. Athanasiou, M.-O. Hongler, and Y. Bellouard, “Unraveling Brittle-Fracture Statistics from Intermittent Patterns Formed During Femtosecond Laser Exposure,” Physical Review Applied 8, (2017).
  • N. Groothoff, M.-O. Hongler, P. Kazansky, and Y. Bellouard, “Transition and self-healing process between chaotic and self-organized patterns observed during femtosecond laser writing,” Optics Express 23, 16993 (2015).
  • Y. Liao, W. Pan, Y. Cui, L. Qiao, Y. Bellouard, K. Sugioka, and Y. Cheng, “Formation of in-volume nanogratings with sub-100-nm periods in glass by femtosecond laser irradiation,” Optics Letters 40, 3623 (2015).
  • Y. Liao, J. Ni, L. Qiao, M. Huang, Y. Bellouard, K. Sugioka, and Y. Cheng, “High-fidelity visualization of formation of volume nanogratings in porous glass by femtosecond laser irradiation,” Optica 2, 329 (2015).
  • R. Drevinskas, M. Gecevicius, M. Beresna, Y. Bellouard, and P. G. Kazansky, “Tailored surface birefringence by femtosecond laser assisted wet etching,” Opt. Express 23, 1428–1437 (2015).
  • Y. Bellouard and M.-O. Hongler, “Femtosecond-laser generation of self-organized bubble patterns in fused silica,” Opt. Express 19, 6807–6821 (2011).

Exploring new manufacturing principles for transparent materials

Thanks to its non‐linearity, femtosecond laser exposure allows for three-dimensional patterning of substrates. It is intrinsically a 3D printing process, allbeit substractive.

The process resolution is dominated by non-linear effects. It can therefore be smaller than the diffraction limit. Features size of a few tens of nanometers have been achieved using this manufacturing principle.

This manufacturing process opens up new design possibilities for miniature and micro‐scale elements with sub‐micron resolution and belongs to the category of 3D printing process.

The picture illustrates a micro-hinge (cross pivot flexure) made out of glass. The three bridges are independant and lie on top of another. Such micro-structures cannot be easily manufactured using classical microsystems fabrication processes, such as lithography-based ones.

  • T. Tičkūnas, M. Perrenoud, S. Butkus, R. Gadonas, S. Rekštytė, M. Malinauskas, D. Paipulas, Y. Bellouard, and V. Sirutkaitis, “Combination of additive and subtractive laser 3D microprocessing in hybrid glass/polymer microsystems for chemical sensing applications,” Opt. Express, OE 25, 26280–26288 (2017).
  • V. Tielen and Y. Bellouard, “Three-Dimensional Glass Monolithic Micro-Flexure Fabricated by Femtosecond Laser Exposure and Chemical Etching,” Micromachines 5, 697–710 (2014).
  • Y. Bellouard, A. Champion, B. Lenssen, M. Matteucci, A. Schaap, M. Beresna, C. Corbari, M. Gecevičius, P. Kazansky, O. Chappuis, M. Kral, R. Clavel, F. Barrot, J.-M. Breguet, Y. Mabillard, S. Bottinelli, M. Hopper, C. Hoenninger, E. Mottay, J. Lopez,”The Femtoprint Project,” Journal of Laser Micro/Nanoengineering 7, 1–10 (2012).

New concept of contact-less packaging

In micro-devices, achieving assembly and packaging with sub-micron resolution is often a daunting challenge and a bottleneck for further integration.

3D Laser‐matter interaction offers an interesting approach for contact-less repositioning of elements with ultrahigh accuracy.

We have demonstrated that femtosecond laser can induce controlled and localized nano-volume changes. By locally distributing these local changes of volume, one can induce local displacement in microscopic structures.

Here, we explore how this principle can be used in complex optical assembly for contact-less, fine positioning of optical elements.

The picture illustrates a close-up view of two flexures of a microstage forming a pivot, viewed in a photoelastic setup. The inset (lower-right corner of the image) shows laser-affected zones consisting of a set of parallel lines that induced a net expansion of the material volume causing a fine motion of the elastic structure.

  • Y. Bellouard, “Non-contact sub-nanometer optical repositioning using femtosecond lasers,” Optics Express 23, 29258 (2015).

New actuating principles

Three‐dimensional machining allows for testing new actuator principles such those based on dielectrophoresis.

The key question is to explore how to move non-conductive objects using electrostatic fields. The working principle is to use a non-linear effect by creating a non-uniform electrostatic field.

This principle is well-known for moving dielectric particles for instance using electrodes carrying travelling-wave field distributions. Here, we investigate its use for moving more complex objects as well as for monolithic glass actuators.

The rationale is to be able to actuate optical elements without the need for depositing electrodes directly on it.

The image shows a close-up view of a monolithic glass device consisting of a cantilever placed in a V-groove shape that is used to create the non-linear electrostatic field distribution. The cantilever remains free of electrodes and is displaced under the action of the electrostatic field.

  • T. Yang and Y. Bellouard, “Laser-Induced Transition between Nonlinear and Linear Resonant Behaviors of a Micromechanical Oscillator,” Physical Review Applied 7, (2017).
  • T. Yang and Y. Bellouard, “Monolithic transparent 3D dielectrophoretic micro-actuator fabricated by femtosecond laser,” Journal of Micromechanics and Microengineering 25, 105009 (2015).
  • B. Lenssen and Y. Bellouard, “Optically transparent glass micro-actuator fabricated by femtosecond laser exposure and chemical etching,” Applied Physics Letters 101, 103503 (2012).

Laser morphing: a step-towards perfect shapes

Manufacturing object with nanometer resolution and yet with overall features sizes of hundreds of microns or more is extremely difficult and requires new approaches.

Here, we investigate how this can be done by transforming a shape into another one. While this idea has been used for creating disc resonators or for melting optical fiber-tips into lenses for instance using CO2 lasers, here, we explore how this concept can be expanded to more complex shapes and eventually generalized.

The picture above is a movie footage, showing a micro-cube manufactured by femtosecond lasers being gradually transformed into a spher. Transforming a shape into another one, for instance using surface tension, offers a path‐way toward perfect shapes such as spheres.

  • J. Drs, T. Kishi, and Y. Bellouard, “Laser-assisted morphing of complex three dimensional objects,” Optics Express 23, 17355 (2015).

Other publications of interest:

  • C. J. de Jong, A. Lajevardipour, M. Gecevičius, M. Beresna, G. Gervinskas, P. G. Kazansky, Y. Bellouard, A. H. A. Clayton, and S. Juodkazis, “Deep-UV fluorescence lifetime imaging microscopy,” Photonics Research 3, 283 (2015).
  • A. Schaap and Y. Bellouard, “Molding topologically-complex 3D polymer microstructures from femtosecond laser machined glass,” Opt. Mater. Express 3, 1428–1437 (2013).
  • C. Corbari, A. Champion, M. Gecevicius, M. Beresna, Y. Bellouard, and P. G. Kazansky, “Femtosecond versus picosecond laser machining of nano-gratings and micro-channels in silica glass,” Opt. Express 21, 3946–3958 (2013).
  • A. Schaap, T. Rohrlack, and Y. Bellouard, “Optical classification of algae species with a glass lab-on-a-chip,” Lab Chip (2012).
  • A. Schaap, T. Rohrlack, and Y. Bellouard, “Lab on a chip technologies for algae detection: a review,” Journal of Biophotonics 5, 661–672 (2012).
  • A. Schaap, Y. Bellouard, and T. Rohrlack, “Optofluidic lab-on-a-chip for rapid algae population screening,” Biomed. Opt. Express 2, 658–664 (2011).
  • D. N. Vitek, E. Block, Y. Bellouard, D. E. Adams, S. Backus, D. Kleinfeld, C. G. Durfee, and J. A. Squier, “Spatio-temporally focused femtosecond laser pulses for nonreciprocal writing in optically transparent materials,” Opt. Express 18, 24673–24678 (2010).
  • D. Tiwari, Y. Bellouard, A. Dietzel, M. Ren, E. Rubingh, and E. Meinders, “Dynamical Observation of Femtosecond-Laser-Induced Bubbles in Water Using a Single Laser Source for Probing and Sensing,” Appl. Phys. Express 3, 127101 (2010).
  • S. Rajesh and Y. Bellouard, “Towards fast femtosecond laser micromachining of fused silica: The effect of deposited energy.,” Optics Express 18, 21490–21497 (2010).
  • F. Madani-Grasset and Y. Bellouard, “Femtosecond laser micromachining of fused silica molds,” Optics Express 18, 21826–21840 (2010).
  • Y. Bellouard, E. Barthel, A. A. Said, M. Dugan, and P. Bado, “Scanning thermal microscopy and Ramananalysis of bulk fused silica exposed to low energy femtosecond laser pulses,” Opt. Express 16, 19520–19534 (2008).
  • Y. Bellouard, M. Dugan, A. A. Said, and P. Bado, “Thermal conductivity contrast measurement of fused silica exposed to low-energy femtosecond laser pulses,” Appl. Phys. Lett. 89, 161911–3 (2006).
  • Y. Bellouard, T. Colomb, C. Depeursinge, M. Dugan, A. A. Said, and P. Bado, “Nanoindentation and birefringence measurements on fused silica specimen exposed to low-energy femtosecond pulses,” Opt. Express 14, 8360–8366 (2006).
  • Y. Bellouard, A. Said, and P. Bado, “Integrating optics and micro-mechanics in a single substrate: a step toward monolithic integration in fused silica,” Opt. Express 13, 6635–6644 (2005).
  • Y. Bellouard, A. Said, M. Dugan, and P. Bado, “Fabrication of high-aspect ratio, micro-fluidic channels and tunnels using femtosecond laser pulses and chemical etching,” Opt. Express 12, 2120–2129 (2004).