The authors present an adaptive algorithm based on a non-linear regression model for mitigating time-varying etalon drifts in line-scanned optical absorption spectrometers. By dynamically varying the etalon spectral background using physically realistic degrees of freedom, the authors’ dynamic etalon fitting-routine (DEF-R) significantly increases the spectral baseline recalibration interval as compared to conventional fringe subtraction models. They provide an empirical demonstration of the efficacy of DEF-R using an on-chip 10 cm silicon waveguide for near-infrared methane absorption spectroscopy at 6057 cm⁻¹, which suffers significant etalon spectral noise due to reflections and multi-path interference from stochastic line-edge roughness imperfections. They demonstrate the corresponding improvement in both spectral clean-up and long-term stability via Allan-variance analysis. For the sensor presented here, application of DEF-R enables Gaussian-noise limited performance for more than 10² s and provides almost an order-of-magnitude improvement in stability time with respect to conventional baseline subtraction. Although DEF-R is applied here to an on-chip sensor embodiment, they envision their technique to be applicable to any absorption sensor limited by time-varying etalon drifts.

We have attempted an overview of fast-pulsating lasers (gain-switched, Q-switched and mode-locked) in various biomedical applications. By necessity, the accents in the chapter have been to an extent coloured by our research experience and interests; apologies are extended to those authors whose work may have been omitted. Different properties of a laser system are important for different applications (e.g., high instantaneous and average power for multiphoton spectroscopy vs. spectral tuning range for OCT), but all the designs above benefit from the properties of semiconductor lasers such as chip compactness, ease of pumping, and high gain per unit length. The use of nanostructures, particularly QDs, has been shown to open new exciting opportunities.

The present chapter serves as a brief introduction to semiconductor light sources mainly laser diodes and light emitting diodes, and the basic physical properties of their semiconductor materials. The chapter also discusses the main reasons for semiconductor light sources being attractive for biomedical applications which range from patient diagnostics imaging to direct treatment such as using photodynamic therapy. It is expected that this specific application area will grow significantly in the future, and that it will be an increasingly important physical properties part of the semiconductor industry.

The intention with this chapter is to briefly review the capabilities made possible in the field of biomedical diagnostics and treatment by employing upconverting nanoparticles (UCNPs), as well as the importance of appropriate light sources for such applications. The field of UCNPs in biomedicine has grown rapidly the last decade, since they first were made sufficiently small and bright to be of real interest for biomedical applications. This research has been reviewed previously, while this chapter will focus on recent advances in the use of UCNPs for preclinical applications and diagnostic assays using laser diode excitation.

Indium tin oxide (ITO) on polyethylene terephthalate (PET) substrate is characterised in terms of pH-sensitivity. Commercial ITO/PET sheet was cut in a shape of electrode and was connected to the gate-terminal of a metal–oxide–semiconductor field-effect transistor as the sensory part, creating an extended gate field-effect transistor (EGFET) pH-sensor. The quality of laser micromachining as well as the moulded ITO/PET electrode is investigated. The pH-sensitivity and linearity of the sensor signal are studied over time for a single hanging ITO/PET electrode. With the help of a constant-charge amplifier circuitry, the reference electrode, dipped in the measurement cell, is grounded. Therefore, the noise level, coupled into the sensor signal from environment, is decreased and also integration of the second sensor to the measurement cell becomes possible. The pH-measurement is carried out while EGFET pair, immersed into a buffer solution next to a pseudo-reference electrode, is working in differential mode to compensate for the high drift signal rate which is common for this type of sensors. As the result, a very low-cost EGFET-based pH-sensor is achieved based on commercially available products independent of costly cleanroom processes.

Intercomparison among six terrestrial laser scanner systems focused on the measurement of small elements ( < 0.5 m) is performed. Phase shift (PS) and time of flight (ToF) scanners are considered. Two standard artefacts containing three-dimensional printing spheres and steps of variable height are used for the experiment. Results show errors between −4.5 and 3.5 mm in the measurement of distances between step planes. The most stable systems for measuring small elements seem the Leica C10, Faro Photon and Riegl LMS Z390i. The quality of the results is linked to the overall quality of the system rather than the specific technology used for range measurement (PS or ToF) which does not appear to be a determining factor.

We propose confocal laser feedback microscopy for in-depth imaging of highly scattering samples. This technique provides a compact configuration for microscopy in reflectance mode; it is based on laser feedback interferometry which is a sensing technique where the laser acts as both transmitter and receiver of the beam. Operating at 850 nm, it offers an ideal platform for non-invasive and in vivo imaging of soft biological tissues. To explore the technique, the authors performed microscopic imaging of micro-glass-spheres (with diameter sizes of 10–20 µm) deep within an agar gel sample, at depth of 0.43 mm from the surface. Experimental results show the feasibility of a compact, low-cost, and simple laser-scanning microscope with possible biomedical imaging applications.

For terahertz systems, rectangular waveguide is an ideal low loss medium for interconnectivity and the construction of passive circuits. A drawback when manufacturing waveguides at submillimeter wavelengths is the demanding tolerances due to small dimensions. For example, a WR-3 waveguide (operating between 220 and 325 GHz) has a cross-sectional dimension of just 864 by 432 µm, and higher frequency waveguides get proportionally smaller. An additional challenge is that whether using waveguide for passive circuits such as filters, there are additional structures inside the waveguide which are significantly smaller than the waveguide itself. Traditionally, computer numerical control (CNC) milling has been used for waveguides, however at terahertz frequencies this is difficult to utilise. Emerging technologies for terahertz waveguides are compared with conventional CNC solutions. The technologies include the photolithography-based polymer etching of waveguides using SU-8 photoresist, and the laser machining of metal. Both have shown promise, and good quality terahertz passive components have been fabricated and measured.

In this study, a laser-assisted bending process is proposed, in which the external force is applied by magnets. The process can be used for bending the magnetic and non-magnetic materials. The experiments indicated that a large bend angle with reduced edge effect can be obtained by this process. The process was simulated by finite element method and a reasonable agreement was obtained between the experimental and simulated bend angles. It was experimentally observed that the micro-hardness after bending was greater than the original micro-hardness for mild steel as well as stainless steel work plates. In all the cases, micro-hardness reduced from laser-irradiated surface to opposite surface. Performance of the process as well as its ability to get accurately simulated bring out its potential of adaptability in industries.