Multiplex Coherent Anti-Stokes Raman Scattering (M-CARS) is an innovative nonlinear spectroscopic approach designed to characterize the vibrational modes of molecular structures. Coherent Raman scattering has been used for the characterization of biomedical targets for about 20 years and the multiplex aspect was introduced 10 years ago thanks to the use of a supercontinuum laser system. For each of these systems, the combination of a pump and a probe wave, driven by an external delay line, is however required to produce the vibrations. In the present work, we propose a new M-CARS system, free of the external delay line. A few-mode microstructured fiber enables merging both wave-packets (pump and supercontinuum) within a single waveguide. We showcase the capability of this system in generating hyperspectral images of biochemically active compounds. Curcumin I, the principal yellow compound isolated from Curcuma longa (Turmeric), is distinguishable by its multiple functional groups that display a nonlinear spectroscopic behavior.
We present a stimulated Raman scattering (SRS) microscope integrated with a novel fiber-based light source. Our light source provides two synchronized pulse trains with 100 mW average power each, independently tunable in the range of 913 to 930 nm and 1024 to 1034 nm, respectively, thus enabling SRS measurements across the 990 to 1300 cm-1 spectral range with a spectral resolution of 15 cm-1. We demonstrate the SRS imaging of leukemic cells recorded in a few seconds. Our system may find potential application in biomedicine, in particular, helping to accelerate the diagnostics and follow-up treatment of leukemia patients.
Since its first demonstration, spatial beam self-cleaning has been targeted as a breakthrough nonlinear effect, for its potential of extending to multimode fibers different technologies based on single-mode fibers, such as fiber lasers and endoscopes. To date, most of the theoretical descriptions of beam self-cleaning are based on scalar models. Whereas, in experiments the analysis of the polarization state of self-cleaned beams is often neglected. Here, we fill this gap between theory and experiments, by demonstrating that a self-cleaned beam eventually loses its degree of polarization, as long as linearly polarized light of enough power is injected at the fiber input. Our results are cast in the framework of a thermodynamic description of nonlinear beam propagation in multimode fibers, providing the first experimental proof of the applicability of scalar theories for the description of the spatial beam self-cleaning effect.
We demonstrate the feasibility of multiphoton fluorescence imaging with high spatial resolution using commercially available single-core 50/125 multimode graded-index fiber. Light propagating forward inside the endoscopic fiber undergoes a non-reciprocal propagation exhibiting a robust nonlinear spatial self-cleaning process. Whereas fluorescence from nonlinear interactions with biological samples linearly propagates backward along the same fiber. The scanner head, located at the distal end of the endoscope and suited for multimode fibers, is based on a ceramic tube where the fiber end follows a spiral course to explore the sample. No knowledge of the fiber transfer matrix is required.
Chirped fiber Bragg gratings opened up a way towards investigating dispersion-managed dissipative soliton regime in all-fiber cavities at the wavelength of 1 µm. It has been shown that dispersion management can decrease the chirped pulse duration compared to all-normal-dispersion oscillators. Recent works also prove that operation near-zero net cavity dispersion can reduce the relative intensity noise. Building such systems using only polarization-maintaining optical fibers is of great interest because of their robustness in extreme environmental conditions resulting in various applications outside research laboratories. This work presents an ultrafast Ybdoped fiber laser oscillator made entirely of polarization-maintaining optical fibers and fiberized components. Unlike in typical ring cavities, the ultrashort pulse passes through the rare-earth-doped fiber twice per cavity roundtrip. The system operates in a Raman-free dispersion-managed dissipative soliton regime at the central wavelength of 1031 nm. The negative dispersion is introduced to the cavity via a chirped fiber Bragg grating. At net cavity dispersion of –0.037 ps2, the setup delivers stable 3 nJ pulses at a repetition rate of 23.781 MHz. The oscillator, passively mode-locked with a nonlinear optical loop mirror, generates positively chirped 8.2 ps pulses, which can be compressed down to 125 fs with a temporal Strehl ratio of 0.77.
This conference presentation, “Spatiotemporal complexity: multimode fiber light sources and their applications” was recorded for the Nonlinear Optics and its Applications 2022 conference at SPIE Photonics Europe 2022.
We present the first all-polarization-maintaining Ytterbium-doped fiber laser oscillator mode-locked through a nonlinear optical loop mirror that works in a dispersion-managed dissipative soliton regime. Using a chirped fiber Bragg grating, we built a cavity of a net negative dispersion delivering ultrashort 2.3 nJ pulses at a repetition rate of 34.08 MHz. Chirped 3.96 ps pulses from the oscillator are recompressible down to 98 fs with a high temporal Strehl ratio.
In this study, we report on experiments of spatio-temporal nonlinear frequency conversion in a periodically poled Lithium Niobate (PPLN) crystal designed for second-harmonic generation (SHG). We demonstrated a novel supercontinuum source based on the mixing of second and third-order nonlinearities. We could adjust the (X(2), X(3)) nonlinearities by controlling the input laser polarization orientation, the pulse duration and the PPLN crystal temperature. We obtained an ultra-broadband spectrum, ranging from visible to infrared domains, by pumping a 20-mm-long PPLN crystal with a 3 ps pulse at 1030 nm. This broadband pulse was used to achieve direct multiplex Coherent Anti-Stokes Raman Scattering (M-CARS) imaging, without the need for any optical delay line to temporally synchronize the pump and the Stokes waves. Simultaneous vibrational signatures ranging from -3200 cm-1 to -500 cm-1 were obtained. Several filters were placed on the broadband supercontinuum path, to shape the output spectrum between 1030 nm and 1650 nm, before sending it into the microscope. The output spectral analysis allows for the demonstration of multimodal imaging, by using SHG, M-CARS and multiphoton fluorescence processes.
Breathing-like dynamics, which is a ubiquitous phenomenon found in numerous physical systems, has recently been observed in mode-locked Erbium-doped fiber lasers. In this paper, we further generalize these fascinating phenomenon by reporting the real-time experimental observations of a breathing-like structure in an all-normal dispersion all-polarization maintaining Ytterbium-doped fiber laser. Contrary to previous studies, we show that the pulsation period increases with the pump power until a stationary dissipative soliton is formed. Our results can help better understand laser physics, and further optimize and improve a fiber cavity design.
We overview recent advances in the research on spatiotemporal beam shaping in nonlinear multimode optical fibers. An intense light beam coupled to a graded index (GRIN) highly multimode fiber undergoes a series of complex nonlinear processes when its power grows larger. Among them, the lowest threshold effect is the Kerr-induced beam self-cleaning, that redistributes most of the beam energy into a robust bell-shaped beam close to the fundamental mode. At higher powers a series of spectral sidebands is generated, thanks to the phase matching induced by the long period grating due to the periodic self-imaging of the beam and the Kerr effect. Subsequently a broadband and spectrally flat supercontinuum is generated, extending from the visible to the mid-infrared.
We demonstrate all-normal dispersion supercontinuum generation in the 1080 nm-1600 nm range by propagating subnanosecond pulses in a high numerical aperture standard optical fiber. The extreme saturation of the Raman gain provides a flat spectrum in the considered range, making this broadband source particularly suitable for coherent Raman spectroscopy. This unusual regime of supercontinuum generation (Raman gain saturation regime) is investigated through an experimental spectrotemporal study. The possibility of operating spectrometer-free time-coded coherent Raman spectroscopy is introduced.
Micro-electro-mechanical systems are exposed to a variety of environmental stimuli, making a prediction of operational
reliability difficult. Here, we investigate environmental effects on properties of piezoelectrically actuated
microcantilevers, where AlN is used as actuation material. The environmental effects to be considered include thermal
and humid cycling, as well as harsh electrical loading performed under normal conditions. Investigated properties are
defined for the static and dynamic behavior of microcantilevers. A Twyman-Green interferometer, operating in both
stroboscopic regime and time-average interferometry mode, is used as a metrology tool. The initial deflection and
frequency changes of the first resonance mode of the microcantilevers are monitored during accelerated thermal aging
tests, humidity tests, as well as harsh electrical loading and fatigue tests. Finally, the resonant fatigue tests accelerated by
application of a high voltage are accomplished to evaluate a lifetime of microcantilevers. Monitoring the
micromechanical behaviors of devices driven by AlN during the lifetime tests assists monitoring of their long-term
stability. FEM calculation is used to identify critical areas of stress concentration in the cantilever structure and to further
explain various failure mechanisms.
Microelectromechanical systems (MEMS) are exposed to a variety of environmental conditions, making the prediction
of operational reliability difficult. In this contribution, we investigate the environmental effects on the static and dynamic
properties of piezoelectrically actuated MEMS microcantilevers where aluminium nitride (AlN) is used as actuation
material. The environmental effects to be considered include thermal and humid cycling, as well as harsh electrical
loading performed under standard weather conditions. Investigated properties are defined for the static behaviour (i.e.
determined initial deflection, out-of-plane displacement vs. constant voltage) and dynamic behaviour (i.e. determined
1st resonance frequency, vibration amplitude at 1st resonance mode) of AlN-based microcantilevers. The metrology tool
is a Twyman Green interferometer, operating in both stroboscopic regime and time-average interferometry mode. The
initial deflection and the frequency changes of the first resonance mode of microcantilevers are monitored during the
accelerated thermal aging, the humidity tests, as well as harsh electrical loading and fatigue tests. Finally, the resonant
fatigue tests, accelerated by application of a high voltage are accomplished to evaluate the lifetime of microcantilevers.
For constant values of voltage higher than 15 V, a delamination of top electrode of AlN transducer is observed.
In this study we focus on the aluminium nitride (AlN). This material shows a large number of advantages associated with
good piezoelectric properties. Therefore, AlN is an excellent candidate for MEMS actuation where low dielectric loss,
low thermal drift and high signal-to-noise ratios are required. In this paper, the case of AlN driven cantilevers composed
of three thin layers deposited on the silicon substrate will be considered. Precise knowledge of physical and material
parameters of AlN applied in these simple elements are necessary for their further applications. However, up to now,
AlN still represents a technological challenge and many of its micromechanical and piezoelectric properties are not
precisely described. That is why, our study has been concentrated on determination of such parameters like the residual
thin film stresses, thermal expansion coefficient α and piezoelectric coefficient d31. In this paper the interactions between
the theoretical solution, the numerical FEM simulations and experimental results were performed. This hybrid
methodology allows to identify the main source of behaviors discrepancy between the physical and numerical model of
tested cantilevers. Obtained knowledge leads to optimization of the technological process and required parameters of
actuator functionality achievement by better understanding of the tested microdevices properties. In experimental
procedure, it was used nanoindentation tests for obtaining an elastic properties of AlN, interferometric techniques for
performing the static and dynamic measurements of cantilevers and scanning electron microscope for measuring
topography.
The subject of this paper is the use of aluminum nitride (AlN) as an actuation layer in MEMS/MOEMS systems. This
material shows a good piezoelectric properties related to deposition conditions. AlN is a promising candidate for the
acoustic wave devices, MEMS applications and sensors what have been already proposed. Up to now, AlN is still a
technological challenge and many of its micromechanical and piezoelectric properties are not precisely described. That is
why our study has been focused on the determination of the material parameters like Young's modulus, residual thin film
stress, piezoelectric coefficient d31 and mechanical behaviour of especially designed cantilevers. To ensure the optimum
design, functionality and reliability of those actuators the theoretical solution and the numerical simulations of
mechanical performance by the Finite Element Method (FEM) were performed. The created model of device takes into
account multiple film stacking. For the characterization it was chosen a full-field optical technique applied in a
multifunctional interferometric platform. Proposed set-up performs the measurement in static and dynamic regimes with
nanometer sensitivity and high spatial resolution. The hybrid method of analysis combining the experimental and
numerical results has been used to better understand the properties of these microdevices, facilitate their designing and to
optimize their technological process. The optimum goal is a developing of the high quality and reliable AlN-driven
cantilevers for use in MEMS/MOEMS.
This study presents static and dynamic characterisation by Twyman Green interferometry of two active MEMS actuators driven by a thin film transducer of aluminium nitride (AlN). Firstly, we report on the testing results of thin film AlN/Si piezoelectric micro-machined ultrasonic transducers. These devices are expected to exhibit sensing capabilities for monitoring fluid property changes. The goal of second case study is the development of reliable AlN driven cantilevers working as actuation elements in Micro-Electro-Mechanical Systems (MEMS).
We discuss on-going reliability studies of micro-optical components and assemblies as conducted in the EU FP6 Network of Excellence on Micro-Optics "NEMO". We focus on three case studies including first biaxial fatigue testing of micro-optical components, second reliability testing and quality control of MEMS and third micro-interferometric tomography for measuring optical fibre refractive index changes. For each of these case studies we discuss the dedicated measurement and characterization methods as well as first results and the perspectives for future research.
The goal of this study was the investigation of reliability of AlN driven cantilevers, operating as MEMS actuators. Some of the fabrication steps being critical in regards to reliability issues, these steps have been firstly optimized. Then the monitoring of fatigue effects produced by thermal loading (130° C) of cantilevers, introducing the evolution of micromechanical parameters has been obtained by Twyman-Green interferometry. The measurements of evolution of resonance frequencies and displacement amplitudes permit the estimation of the long-term stability of such AlN based actuators.
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