arXiv subjects

Bernhard Lendl

Publications and source records attributed to Bernhard Lendl.

10 recordsLinked to original sources

arXiv2026

Infrared photonics for healthcare: A roadmap for proactive and predictive health management

The field of infrared (IR) photonics is currently undergoing remarkable progress, moving rapidly towards practical sensing applications demanded by medical therapy and diagnostics (theranostics). The Developments can be divided into three main categories: (i) novel devices and measurement concepts including advanced updates of classical approaches that push medical sensing into the spotlight; (ii) new demonstrations of photonic integrated circuit (PIC-)based IR devices enabling highly miniaturized sensors for point-of-care application as well as medical and wellness wearables; and (iii) technologically-mature IR demonstrators that enable first medical sensing and treatment applications. This roadmap paper provides a consolidated overview of this highly dynamic and interdisciplinary research field with a focus on the major roadblocks that limit the widespread adoption of IR photonics in large-scale medical diagnostics. Special attention is given to the ambivalence between the molecular-level spectroscopic interpretation and a broader health-state assessment, highlighting the need for a common framework. Additionally, the paper discusses the critical importance of unified measurement standards, calibration protocols, and medical certification processes to ensure the validity of experimental results, reproducibility, and clinical trust, particularly when novel experimental techniques and AI algorithms are involved. Perspectives from major past and current contributors to application-oriented IR photonics will be provided.

physics.app-ph↗

arXiv2024

Absorption and Dispersion: In Search of a Versatile Spectroscopic Technique

This paper investigates three spectroscopic techniques - Tunable Diode Laser Absorption Spectroscopy (TDLAS), Wavelength Modulation Spectroscopy (WMS), and Heterodyne Phase Sensitive Dispersion Spectroscopy (HPSDS) - to evaluate their performance in detecting carbon monoxide (CO) in nitrogen in a 31 m Herriot cell using an Interband Cascade Laser (ICL) emitting at 4559 nm. With the developed spectrometer, we can switch between the techniques with minimal hardware modifications. Calibration curves were established using simple peak-to-peak values from the recorded TDLAS, WMS, and HSPDS spectra, as well as after applying respective spectral models of the sensor responses followed by a least-squares fitting approach. We compare the results when using the different techniques with respect to obtained linearity, minimum detectable value (MDV), standard deviation of the method (sx0), coefficient of variation of the method (Vx0), limit of detection (LOD), and Allan-Werle deviation analysis. The results show significant differences in the performance of the three techniques when establishing calibration curves based on peak-to-peak evaluation of the recorded spectra. However, when establishing model-based calibration curves, a more uniform performance of the investigated techniques was found. The results demonstrate that TDLAS is a straightforward and robust technique but has a limited measurement range of up to 65 ppm. WMS offers a linear range of up to 100 ppm if an appropriate spectral model is applied and a baseline-free operation but requires careful calibration. HPSDS stands out for its wide linear range of up to 100 ppm and immunity to power fluctuations. However, its operation requires a complex mathematical model and radio frequency (RF) components.

physics.ins-det↗

arXiv2024

All-mirror wavefront division interferometer for mid-infrared spectrometry

We report on the design of an all-mirror wavefront-division interferometer capable of spectroscopic studies across multiple spectral ranges$\unicode{x2013}$from the plasma frequencies of metals to terahertz wavelengths and beyond. The proposed method leverages the properties of laser sources with high spatial coherence. A theoretical framework for the interferometer scheme is presented, along with an analytical solution for determining the far-field interference pattern, which is validated through both optical propagation simulations and experimental results. The practical implementation of the spectrometer, using cost-effective off-the-shelf components (knife-edge prisms for separation and recombination), is demonstrated. The system features ultra-broad optical bandwidth, high throughput, simple architecture, dispersion-free operation, and variable arm split ratio. These unique attributes make our approach a prospective alternative to standard Fourier transform spectrometer schemes, specifically tailored to laser-based scenarios. Further, the employed design inherently enables the measurement of the sample's dispersion. In the experimental section, we demonstrate the feasibility of spectroscopic measurements by coupling the system with a supercontinuum source with more than an octave-spanning range (1.5 $cm^{-1}$ - 4.4 $cm^{-1}$). As a proof-of-concept, an experimental demonstration is provided for various applied spectroscopic studies: transmission measurements of polymers (polypropylene) and gas (methane), as well as reflectance measurements of dried pharmaceuticals (insulin products on a metal surface).

physics.optics↗

arXiv2023

Surface Protection and Activation of Mid-IR Plasmonic Waveguides for Spectroscopy of Liquids

Liquid spectroscopy in the mid-infrared spectral range is a very powerful, yet premature technique for selective and sensitive molecule detection. Due to the lack of suitable concepts and materials for versatile miniaturized sensors, it is often still limited to bulky systems and offline analytics. Mid-infrared plasmonics is a promising field of current research for such compact and surface-sensitive structures, enabling new pathways for much-needed photonic integrated sensors. In this work, we focus on extending the concept of Ge/Au-based mid-infrared plasmonic waveguides to enable broadband liquid detection. Through the implementation of high-quality dielectric passivation layers deposited by atomic layer deposition (ALD), we cover the weak and water-soluble Ge native oxide. We show that approximately 10 nm of e.g. Al2O3 or ZrO2 can already protect the plasmonic waveguides for up to 90 min of direct water exposure. This unlocks integrated sensing schemes for broadband molecule detection based on mid-infrared plasmonics. In a proof-of-concept experiment, we further demonstrate that the ZrO2 coated waveguides can be activated by surface functionalization, allowing the selective measurement of diethyl ether at a wavelength of 9.38 μm.

physics.optics↗

arXiv2023

Advanced Mid-Infrared Plasmonic Waveguides For On-Chip Integrated Photonics

Long-wave infrared (LWIR, 8-14 um) photonics is a rapidly growing research field within the mid-IR with applications in molecular spectroscopy and optical free-space communication. LWIR-applications are often addressed using rather bulky tabletop-sized free-space optical systems, preventing advanced photonic applications such as rapid-time-scale experiments. Here, device miniaturization into photonic integrated circuits (PICs) with maintained optical capabilities is key to revolutionize mid-IR photonics. Sub-wavelength mode confinement in plasmonic structures enabled such miniaturization approaches in the visible-to-near-IR spectral range. However, adopting plasmonics for the LWIR needs suitable low-loss and -dispersion materials with compatible integration strategies to existing mid-IR technology. In this work we further unlock the field of LWIR/mid-IR PICs, by combining photolithographic patterning of organic polymers with dielectric-loaded surface plasmon polariton (DLSPP) waveguides. In particular, polyethylene shows favorable optical properties, including low refractive index and broad transparency between ~2-200 um. We investigate the whole value chain, including design, fabrication, and characterization of polyethylene-based DLSPP waveguides and demonstrate their first-time plasmonic operation and mode guiding capabilities along s-bend structures. Low bending losses of ~1.3 dB and straight-section propagation lengths of ~1 mm, pave the way for unprecedented, complex on-chip mid-IR photonic devices. Moreover, DLSPPs allow full control of the mode parameters (propagation length and guiding capabilities) for precisely addressing advanced sensing and telecommunication applications with chip-scale devices.

physics.optics↗

arXiv2021

Spectrally resolved linewidth enhancement factor of a semiconductor frequency comb

The linewidth enhancement factor (LEF) has recently moved into the spotlight of research on frequency comb generation in semiconductor lasers. Here we present a novel modulation experiment, which enables the direct measurement of the spectrally resolved LEF in a laser frequency comb. By utilizing a phase-sensitive technique, we are able to extract the LEF for each comb mode. We first investigate and verify this universally applicable technique using Maxwell-Bloch simulations and then present the experimental demonstration on a quantum cascade laser frequency comb.

physics.optics↗

arXiv2020

Correlative infrared optical coherence tomography and hyperspectral chemical imaging

Optical coherence tomography (OCT) is a high-resolution three-dimensional imaging technique that enables non-destructive measurements of surface and subsurface microstructures. Recent developments of OCT operating in the mid-infrared (MIR) range (around 4 μm) lifted fundamental scattering limitations and initiated applied material research in formerly inaccessible fields. The MIR spectral region, however, is also of great interest for spectroscopy and hyperspectral imaging, which allow highly selective and sensitive chemical studies of materials. In this contribution, we introduce an OCT system (dual-band, central wavelengths of 2 μm m and 4 μm) combined with MIR spectroscopy that is implemented as a raster scanning chemical imaging modality. The fully-integrated and cost-effective optical instrument is based on a single supercontinuum laser source (emission spectrum spanning from 1.1 μm to 4.4 μm). Capabilities of the in-situ correlative measurements are experimentally demonstrated by obtaining complex multidimensional material data, comprising morphological and chemical information, from a multi-layered composite ceramic-polymer specimen.

physics.optics↗

arXiv2020

Sensitivity-enhanced Fourier transform mid-infrared spectroscopy using a supercontinuum laser source

Fourier transform infrared (FTIR) spectrometers have been the dominant technology in the field of mid-infrared (MIR)spectroscopy for decades. Supercontinuum laser sources operating in the MIR spectral region now offer the potential to enrich the field of FTIR spectroscopy due to their distinctive properties, such as high-brightness, broadband spectral coverage and enhanced stability. In our contribution, we introduce this advanced light source as a replacement for conventional thermal emitters. Furthermore, an approach to efficient coupling of pulsed MIR supercontinuum sources to FTIR spectrometers is proposed and considered in detail. The experimental part is devoted to pulse-to-pulse energy fluctuations of the applied supercontinuum laser, performance of the system, as well as the noise and long-term stability. Comparative measurements performed with a conventional FTIR instrument equipped with a thermal emitter illustrate that similar noise levels can be achieved with the supercontinuum-based system. The analytical performance of the supercontinuum-based FTIR spectrometer was tested for a concentration series of aqueous formaldehyde solutions in a liquid flow cell (500 $μ$m path length) and compared with the conventional FTIR (130 $μ$m path length). The results show a four-times-enhanced detection limit due to the extended path length enabled by the high brightness of the laser. In conclusion, FTIR spectrometers equipped with novel broadband MIR supercontinuum lasers could outperform traditional systems providing superior performance, e.g., interaction path lengths formerly unattainable, while maintaining low noise levels known from highly stable thermal emitters.

physics.ins-det↗

arXiv2020

Resonant Tunneling Diodes Strongly Coupled to the Cavity Field

We demonstrate Resonant Tunneling Diodes, embedded in double metal cavities, strongly coupled to the cavity field, while maintaining their electronic properties. We measure the polariton dispersion and find a relative vacuum Rabi splitting of 16%, which explicitly qualifies for the strong-coupling regime. Additionally we show that electronic transport has a significant influence on the polaritons by modulating the coupling strength. The merge between electronic transport and polaritonic physics in our devices opens up a new aspect of cavity quantum electro-dynamics and integrated photonics.

cond-mat.mes-hall↗

arXiv2020

Ultra-sensitive refractive index gas sensor with functionalized silicon nitride photonic circuits

Portable and cost-effective gas sensors are gaining demand for a number of environmental, biomedical and industrial applications, yet current devices are confined into specialized labs and cannot be extended to general use. Here, we demonstrate a part-per-billion-sensitive refractive index gas sensor on a photonic chip based on silicon nitride waveguides functionalized with a mesoporous silica top-cladding layer. Low-concentration chemical vapors are detected by monitoring the output spectral pattern of an integrated Mach-Zehnder interferometer having one coated arm exposed to the gas vapors. We retrieved a limit of detection of 65 ppb, 247 ppb and 1.6 ppb for acetone, isopropyl alcohol and ethanol, respectively. Our on-chip refractive index sensor provides, to the best of our knowledge, an unprecedented sensitivity for low gas concentrations based on photonic integrated circuits. As such, our results herald the implementation of compact, portable and inexpensive devices for on-site and real-time environmental monitoring and medical diagnostics.

physics.ins-det↗