GHz repetition rate, sub-100-fs Ho:CALGO laser at 2.1†µm with watt-level average power.

We report on a GHz fundamental repetition rate Kerr-lens mode-locked Ho:CALGO laser emitting at 2.1 µm. The laser employs a ring cavity to increase the fundamental repetition rate to 1.179 GHz and can be made to oscillate in both directions stably with nearly identical performance: for the counterclockwise oscillation, it generates 93-fs pulses at 1.68 W of average power, whereas 92 fs and 1.69 W were measured for the clockwise operation. Our current results represent the highest average power from a 2-µm GHz oscillator and, to our knowledge, the first sub-100-fs pulse duration from a Ho-based oscillator.

Enhanced Tracer Particle Detection in Dynamic Bulk Systems Based on Polarimetric Radar Signature Correlation.

This contribution focuses on the detection of tracer particles within non-homogeneous bulk media, aiming to enhance insights into particulate systems. Polarimetric radar measurements are employed, utilizing cross-polarizing channels in order to mitigate interference from bulk media reflections. To distinguish the tracer particle in the measurements, a resonant cross-polarizing structure is constructed, facilitating the isolation of frequency signatures from the surrounding bulk clutter. In addition to characterizing the bulk and tracer components, this study provides a detailed presentation and discussion of the measurement setup, along with the employed signal processing methods. The effectiveness of the proposed methods is demonstrated through comprehensive measurements, where a tracer particle is systematically positioned at various locations. The results affirm the feasibility and efficacy of the approach, highlighting its applicability for enhanced dynamic monitoring in particulate systems within industrial processes.

Low-noise, 2-W average power, 112-fs Kerr-lens mode-locked Ho:CALGO laser at 2.1†µm.

We report on an in-band pumped soft-aperture Kerr-lens mode-locked Ho3+-doped CaGdAlO4 (Ho:CALGO) bulk laser at 2.1 µm, generating 2 W of average power with 112 fs pulses at 91-MHz repetition rate. To the best of our knowledge, this is the highest average power from a 100-fs class mode-locked laser based on a Tm3+ or Ho3+ doped bulk material. We show that the laser has excellent noise properties, with an integrated relative intensity noise of 0.02% and a timing jitter of 950 fs (rms phase noise 0.543 mrad) in the integration interval from 10 Hz to 10 MHz of offset frequency. The demonstrated combination of high average power, short pulses, and low noise makes this an outstanding laser source for many applications at 2.1 µm.

A Novel Localization System in SAR-Demining Applications Using Invariant Radar Channel Fingerprints.

In this paper, we present a novel two dimensional (2D) frequency-modulated continuous-wave (FMCW) localization method for handheld systems based on the extraction of distinguishable subchannel fingerprints. Compared with other concepts, only one subdivided radar source channel is needed in order to instantly map a one-dimensional measurement to higher-dimensional space coordinates. The additional information of the detected target is implemented with low-cost hardware component features, which exhibit distinguishable space-dependent fingerprint codes. Using the given a priori information of the hardware thus leads to a universally applicable extension for low-cost synthetic aperture radar (SAR)-demining purposes. In addition to the description of the system concept and its requirements, the signal processing steps and the hardware components are presented. Furthermore, the 2D localization accuracy of the system and the classification accuracy of the frequency-coded fingerprints are described in a defined test environment to proof the operational reliability of the realized setup, reaching a classification accuracy of 94.7% and an averaged localization error of 4.9 mm.

Enhancing the Radar Cross-Range Resolution in Ultra-Fast Radar Scans by Utilizing Frequency Coded Sub-Channels.

This contribution handles a single-channel radar method that utilizes frequency-coded sub-channels for enabling cross-range resolution. Because of the sub-channel coding, the whole area of interest (AOI) is scanned within a single radar measurement. To further enhance the cross-range resolution, the sub-channels' antenna beams are overlaid in this work, resulting in multiple coding signatures. Next to the operation theory, hardware components, such as coding filters and antennas, as well as signal processing methods, are presented and discussed in detail. A final measurement campaign that investigates several radar scenarios reveals high detection properties and proves the applicability of the proposed radar method.

A Compact Measurement Setup for Material Characterization in W-Band Based on Dielectric Waveguides.

In this contribution, we present a measurement system for material characterization in the millimeter-wave range that requires extremely small amounts of sample material. With the help of a dielectric waveguide, it is possible to measure the complete S-parameters with only one port. Fundamentals regarding dielectric waveguides and algorithms are explained, which form the basis of the measurement system. Within the scope of this work, an existing waveguide system was extended and optimized. In addition, two algorithms were implemented to determine permittivity. Finally, measurements were carried out to prove the function of the measurement setup and compared to existing measurement setups.

Field Representation Microwave Thermography Utilizing Lossy Microwave Design Materials.

In this contribution, we are investigating a technique for the representation of electromagnetic fields by recording their thermal footprints on an indicator material using a thermal camera. Fundamentals regarding the interaction of electromagnetic heating, thermodynamics, and fluid dynamics are derived which allow for a precise design of the field illustration method. The synthesis and description of high-loss dielectric materials is discussed and a technique for a simple estimation of the broadband material's imaginary permittivity part is introduced. Finally, exemplifying investigations, comparing simulations and measurements on the fundamental TE10-mode in an X-band waveguide are presented, which prove the above introduced sensing theory.

A Newly Developed mm-Wave Sensor for Detecting Plaques of Arterial Vessels.

BACKGROUND: Microcalcifications within the fibrous cap of the arteriosclerotic plaques lead to the accrual of plaque-destabilizing mechanical stress. New techniques for plaque screening with small detectors and the ability to differentiate between the smooth and hard elements of plaque formation are necessary. METHOD: Vascular plaque formations are characterized as calcium phosphate containing structures organized as hydroxylapatite resembling the mineral whitlockite. In transmission and reflexion studies with a simple millimeter wave (mm-wave)-demonstrator, we found that there is a narrow window for plaque detection in arterial vessels because of the tissue water content, the differentiation to fatty tissue, and the dielectric property of air or water, respectively. RESULT: The new sensor is based on a sensing oscillator working around 27 GHz. The open-stub capacitance determines the operating frequency of the sensor oscillator. The capacitance depends on the dielectric properties of the surrounding material. The sensor components were completely built up in surface mount technique. CONCLUSION: Completed with a catheter, the sensor based on microwave technology appears as a robust tool ready for further clinical use.

Ultrasonic and conversion-based inline fouling measurements for continuous emulsion copolymerisation of vinyl acetate in a tubular reactor.

One of the serious challenges for the implementation of continuous emulsion polymerisation is their significant fouling. The elucidation of time-dependent fouling processes and the development of inline analysis methods for fouling mass quantification are crucial to making progress in this area. Inline-sensor concepts based on ultrasonic measurements as well as residence time and conversion analysis were investigated regarding their suitability for the detection of time-dependent fouling formation and compared with gravimetrical results in order to validate their precision. Both a set-up using a turnover analysis for determination of losses in reaction volume by fouling and an ultrasound-based measurement system detecting deposit-caused changes by evaluating the average sound velocity could be used as suitable sensor concepts. The accuracies of both sensors are below 10% deviation to fouling references.