Abstract Photodermatoses such as solar urticaria and chronic actinic dermatitis cause heightened sensitivity to outdoor and, in some cases, indoor light, leading to pain, pruritus and prolonged erythema. These conditions substantially affect quality of life, with rates of psychological comorbidity higher than in the overall population. Management relies on rigorous photoprotection and limiting exposure to ultraviolet and visible light, yet many patients struggle to judge real-time light conditions and remain uncertain when cumulative exposure may reach their individual symptom threshold. Few tools provide personalized, objective feedback to help guide everyday decisions about light avoidance. Following discussions with patients, we explored the potential of repurposing ExpoDose®, a research-grade solar monitoring platform, as a support tool for managing photosensitivity. ExpoDose® integrates GPS-derived location and satellite irradiance data to estimate ambient solar exposure through a smartphone app. The APPETISER study (Assisting Photosensitive Patients Excel Through Information on Sun Exposure: a Realism Study) was developed as a clinical service initiative to evaluate technical feasibility, usability and perceived value for individuals living with photosensitivity. Engagement was high, with 89% of participants using the app daily and reporting it to be easy to use. Overall, 78% expressed at least some level of satisfaction, and 67% felt their ability to manage photosensitivity improved during the evaluation. When asked to rate the app’s contribution to this improvement on a 0–10 scale, the mean score was 7. Although 89% wished to continue using the app, only 11% were willing to pay for it in its current form. A 35% dropout rate, largely due to technical issues, influenced overall outcomes. Nonetheless, patient responses demonstrated strong interest in tools that help contextualize daily solar exposure and support self-management. Although the app will not enter routine practice, future work will explore what motivates behaviour change among people living with photodermatoses.

Managing photosensitivity conditions, including polymorphic light eruption (PLE), chronic actinic dermatitis (CAD), solar urticaria (SU) and cutaneous porphyria, necessitates comprehensive photoprotection strategies. Sunscreens, a cornerstone of these strategies, can pose unique challenges for photosensitive individuals, who may not have an ultraviolet or visible light sensitivity that corresponds to the standard erythema curve. This can mean sunscreen effectiveness for these individuals is not adequately addressed by the product’s sun protection factor (SPF). However, if an individual has heightened visible light sensitivity, as typically seen in SU or porphyria, this does not necessarily mean a visible light-protecting sunscreen is the best choice. This was previously shown for a patient with visible light-sensitive SU who had greater effectiveness with an SPF 50+ formulation without visible light filters compared with one that did. It is thus challenging for people with photosensitivity to know how to select an appropriate sunscreen or for clinicians to advise on optimal choices. This study aimed to evaluate real-world sunscreen usage among photosensitive individuals, exploring factors involved in sunscreen choices, including the role and importance of UV and visible light protection. A structured questionnaire was developed and distributed through the Scottish Photobiology Service and the British Porphyria Association to individuals with a range of photosensitivity conditions, collecting data on sunscreen preferences, usage challenges and visible light protection awareness. There were 82 responses. Difficulties with sunscreen use were reported by 44%, with approximately half expressing dissatisfaction with certain products. Variations in adoption of visible light-protecting sunscreens were observed across conditions. For individuals with CAD, 17% used visible-protecting sunscreen and 50% did not; 33% were not ascertained (NA). For individuals with SU, only 8% used visible-protecting sunscreens and 58% did not (33% NA). With PLE, 43% used visible-protecting sunscreens and 43% did not (14% NA). For photosensitive porphyria, 56% confirmed visible-protecting sunscreen usage, while 32% did not (12% NA). Those without a clear photosensitivity diagnosis showed the lowest uptake of visible-protecting sunscreens (0%), with 65% not using them (35.3% NA). These findings highlight the complexity of sunscreen choices and usage for photosensitive individuals. Given that almost half of responders with porphyria, and > 90% of those with SU, were not using visible-protecting sunscreens, this also highlights the challenges for clinicians in recommending sunscreen choices based on diagnosis, although further detailed evaluation into the reasons behind sunscreen choices is required. Close collaboration with industry is needed to highlight the specific challenges of sunscreen choices for patients with photosensitivity diseases, with emphasis on individualized approaches as the mainstay of photoprotection.

BACKGROUND/OBJECTIVES:Individuals with photosensitivity diseases, including porphyria, face significant challenges in managing their condition due to heightened sensitivity to ultraviolet (UV) and visible light. Comprehensive photoprotection strategies are essential and prioritize environmental modifications, behavioral adjustments, protective clothing, and hats. Sunscreens serve as a supplementary measure, particularly for exposed skin areas not otherwise protected. However, the extensive variety of available sunscreen products and limited guidance on their efficacy complicate the selection process. This study evaluates sunscreen use among photosensitive individuals and gathers feedback to inform future service development and research. METHODS:A questionnaire was completed by 32 individuals with porphyria (mostly with porphyrias causing skin photosensitivity) and 50 individuals with non-porphyric photosensitivity conditions, totaling 82 participants. The survey assessed preferences and experiences with sunscreens, focusing on criteria such as protection efficacy, cost, availability, and ease of use. Responses were analyzed to identify trends and challenges in integrating sunscreens into broader photoprotection strategies. RESULTS:Protection efficacy was the primary factor influencing sunscreen choice among photosensitive patients, highlighting its importance alongside other photoprotection measures. The survey revealed considerable variation in sunscreen use. La Roche-Posay was the most favored brand. While 56% of porphyria patients used sunscreens explicitly labelled for visible light protection, only 11% of non-porphyric patients did so. Overall, 40% of participants reported issues with sunscreens, and approximately half expressed dissatisfaction with certain products, emphasizing the need for more effective and user-friendly options. CONCLUSIONS:Sunscreens are a critical adjunct to broader photoprotection strategies for photosensitive patients but are not a standalone solution. Particularly for those with porphyrias, effectiveness was regarded as especially important. The variability in product preferences and the frequent difficulties reported highlight the need for improved guidance and accessibility of sunscreens tailored to diverse photosensitivity needs. Future research should focus on developing clear recommendations and expanding options to ensure effective and personalized photoprotection.

This pilot study evaluated the design, usability, and practicality of the dPDT@home kit for treating actinic keratoses (AKs) on the face and scalp. The kit allowed patients to manage their treatment at home, reducing hospital visits and utilizing natural sunlight. While patients were very willing to use the kit again, further studies are required to evaluate outcomes and ascertain the need for additional improvements and support. Background/Objectives: Daylight photodynamic therapy (dPDT) is an established effective therapy for superficial mild-to-moderate actinic keratoses (AKs) on the face and scalp. In this project, we redesigned the delivery of dPDT using design principles and the concept of Realistic Medicine to create the dPDT@home kit. This user-friendly and environmentally conscious kit allows patients to manage their AKs at home, reducing the need for hospital visits and ensuring timely treatment to coincide with appropriate weather conditions and to prevent disease progression due to delays in diagnosis and treatment. The initial pilot phase of the study was to evaluate the usability and convenience of the practicalities of the dPDT@home kit. Methods: Patients were instructed to conduct two dPDT@home kit treatments approximately three weeks apart on suitable weather days. After a follow-up telephone consultation from the specialist PDT nurse following the first treatment, patients then completed an initial questionnaire (Questionnaire 1, Q1) to share their experience. A second questionnaire (Q2) was completed 3-6 months after their final treatment to assess treatment outcomes. Results: A total of 16 patients with AK on the face and/or scalp used the dPDT@home kit. Five patients formed an initial pilot group in 2020/21, whose feedback and involvement informed the final product for the larger group of eleven patients (2021/22). All patients reported no issues with receiving the kit or the pro-drug used in the treatment (Q1). Q2 had an 81.25% return rate, with an average willingness score of 8.9/10 to use dPDT@home again. However, patients expressed doubts about their confidence in the treatment's efficacy, giving an average score of 6.9/10, with preferences leaning towards other treatments, such as hospital-based PDT or cryotherapy. Conclusions: The pilot deployment of the dPDT@home kit identified suitable patients and highlighted the need for comprehensive training and support for both patients and clinicians to deliver dPDT through this novel approach. The kit can reduce the number of hospital visits, but patients still require supervision, which can be provided remotely. The questionnaire outcomes emphasize the importance of setting patient expectations and taking a holistic approach to managing chronic field-change AK. Additionally, the kit's recyclable components and reliance on natural sunlight promote sustainability and reduce patient travel. Further evaluation is required to determine cost-efficacy, safety, and the potential place of the dPDT@home kit in the therapeutic management of patients with this common and challenging condition.

We propose mode-locked laser diodes (MLLDs) for their deployment in a low-cost and portable optical coherence tomography (OCT) system. OCT is an essential imaging technique used for medical diagnoses in dermatology, ophthalmology, and cardiology. Based on low-coherence interferometry, OCT directs infrared light through various layers of tissue, which is reflected onto a detector and resolved as an image. Generally, swept-source OCT (SS-OCT) systems perform better than grating based systems and time domain OCT but require expensive laser sources which are optically pumped, meaning they require an additional pump laser, limiting their deployment in clinics. To that end we propose MLLDs as an excellent candidate to realize, low-cost, compact, and portable SS-OCT enabled by their fast electronic tuning and electrically pumped, monolithic construction. We present simulated SS-OCT images using experimentally measured spectra from our InAs Quantum-Dot MLLDs and compare this to simulated data using a Thorlabs research-grade micromechanically tuned VCSEL (vertical cavity surface emitting lasers). Our first results to date suggest MLLDs could resolve features of 62.5 mu m, which, compared with the off-the-shelf system, is approximately half the resolution. Further studies suggest that by examining electronic fine- tuning of the spectral linewidths and central wavelength, MLLDs may be highlighted as a key tool in realizing low-cost portable OCT at comparable quality to existing research-grade systems. Couple this with the current shift in practices to complex image analysis using machine learning methods, a handheld SS-OCT system could be realized as a low-cost, compact and versatile tool for clinicians.

We report the design and characterization of a femtosecond optical parametric oscillator containing an intracavity Herriott cell. Pumped by a 49.16-MHz Yb:fiber laser, the signal wavelength could be tuned over 1440-1530 nm, with the Herriott cell containing 81% of the free-space cavity length required for synchronous operation. We also report a 12.29-MHz OPO using a sub-harmonic pumping approach, extending the Herriott cell OPO concept to low-repetition-rate cavities.

Phototherapy clinics administer ultraviolet (UV) light to patients using phototherapy cabinets. The UV radiation from these cabinets is reflected on the white ceiling tiles of the clinic and is then redirected toward both staff and patients in the area. This is particularly problematic for clinical technologists who must undertake dosimetry in these areas and have a specific time (often as low as 30 min) before they reach their maximum exposure limit. By replacing white tiles with black ones, which absorb any stray radiation, we were able to reduce stray reflection by almost 90%, prolonging the time to maximum exposure by nearly 10 times. We present these findings to encourage other similar clinics to undertake the simple protocols outlined in this article, which will significantly improve staff and patient safety. Ultraviolet radiation from phototherapy cabinets reflects on the white ceiling tiles of hospital clinics and is redirected towards staff and patients in these clinical areas. By replacing white tiles with black ones, we have been able to reduce such reflection by almost 90%, prolonging the time to maximum exposure by nearly 10 times.

Three-photon fluorescence microscopy exploits a tissue transparency window around $1.6-1.8\ \mu \mathrm{m}$ to enable imaging at greater depths than can be achieved using two-photon fluorescence [1], but typically requires expensive few-MHz laser sources such as optical parametric amplifiers (OPAs). Such systems are optically inefficient, requiring bulky, high-average-power pump lasers. An ultrafast optical parametric oscillator (OPO) can in theory provide the same performance with a fraction of the pump power, yet requires a long cavity length to achieve few-MHz operation in a synchronous configuration. To address this issue we present a synchronously-pumped OPO which employs an intracavity Herriott cell (HC) [2] to provide the same optical path in a compact footprint.

We present a theoretical overview and a proposed methodology which demonstrates SLASOPS (single laser asynchronous optical sampling) as a single-laser alternative to the conventional two-laser ASOPS technique. We propose the optical and electronic setup in which SLASOPS may be achieved experimentally with a single 2-section mode-locked laser diode as the pulsed-laser source and simulate how asynchronous optical sampling is generated and detected theoretically. We highlight the technique’s ability to provide customizable scan ranges, scan rates and scan resolutions through variation of the imbalance in the interferometer arms and by tuning the repetition rate of the pulsed-laser source, which we present as optical cross-correlations between pulse pairs. We incorporate jitter into the system mathematically to assess the limitations on resolving both intensity and interferometric cross-correlation traces and to investigate the effects of averaging such traces in real-time. Analysis is then carried out on cross-correlation trace amplitude, width, and temporal positioning in order to discuss the technique’s ability for deployment in typical optical sampling applications. In particular we note SLASOPS’ ability to conduct asynchronous optical sampling using only a single laser, halving both the expense and technical requirements, doing so at megahertz scan rates, and within a spatial precision of just a few microns.

Fiber-feedback optical parametric oscillators (OPOs) incorporate intracavity fibers to provide a compact high-energy wavelength-tunable laser platform; however, dispersive effects can limit operation to the sub-picosecond regime. In this research article, we modeled pulse propagation through systems of cascaded fibers, incorporating SMF-28 and ultra-high numerical aperture (UHNA) fibers with complementary second-order dispersion coefficients. We found that the pulse duration upon exiting the fiber system is dominated by uncompensated third-order effects, with UHNA7 presenting the best opportunity to realise a cascaded-fiber-feedback OPO.

We propose SL-ASOPS - Single Laser Asynchronous Optical Sampling; the theory of performing fast two-laser style asynchronous optical sampling, using only one laser, halving the costs and complexity for applications from metrology to life sciences.

This paper demonstrates optical sampling by electronic repetition-rate tuning (OSBERT): a single-laser optical sampling technique capable of fast scan rates and customisable scan ranges. The method has no moving parts and is based on the electronic modulation of the repetition rate of a passively mode-locked laser diode, simply by varying the reverse bias applied directly to the saturable absorber section of the laser. Varying the repetition rate in a system built as a highly imbalanced interferometer results in pairs of (pump, probe) pulses with successive increasing delay. The resulting scan range is proportional to the magnitude of the repetition rate modulation and is scaled by the chosen length of the imbalance. As a first proof of concept, we apply the method to distance measurement, where the displacement of a target across 13.0 mm was detected with ∼0.1 mm standard deviation from an equivalent free-space distance of 36 m and at a real-time scan rate of 1 kHz. The customizable scan range and competitive scan rate of the method paves the way for single ultrafast semiconductor laser diodes to be deployed as fast, low-cost, and compact optical sampling systems in metrology, biomedical microscopy, and sensing applications.

We demonstrate, for the first time, optical sampling by repetition-rate tuning (OSBERT) at record megahertz scan rates. A low-cost, tunable and extremely compact 2-section passively mode-locked laser diode (MLLD) is used as the pulsed laser source, whose repetition rate can be modulated electronically through biasing of the saturable absorber section. The pulsed output is split into two arms comparable to an imbalanced Michelson interferometer, where one arm is significantly longer than the other (a passive delay line, or PDL). The resulting electronic detuning of the repetition rate gives rise to a temporal delay between pulse pairs at a detector; the basis for time-resolved spectroscopy. Through impedance-matching, we developed a new system whereby a sinusoidal electrical bias could be applied to the absorber section of the MLLD via a signal generator, whose frequency could be instantly increased from sub-hertz through to megahertz modulation frequencies, corresponding to a ground-breaking megahertz optical sampling scan rate, which was experimentally demonstrated by the real-time acquisition of a cross-correlation trace of two ultrashort optical pulses within just 1 microsecond of real time. This represents scan rates which are three orders of magnitude greater than the recorded demonstrations of OSBERT to date, and paves the way for highly competitive scan rates across the field of time-resolved spectroscopy and applications therein which range from pump probe spectroscopy to metrology.

Electron cloud ( e -cloud) mitigation is an essential requirement for proton circular accelerators in order to guarantee beam stability at a high intensity and limit the heat load on cryogenic sections. Laser-engineered surface structuring is considered a credible process to reduce the secondary electron yield (SEY) of the surfaces facing the beam, thus suppressing the e -cloud phenomenon within the high luminosity upgrade of the LHC collider at CERN (HL-LHC). In this study, the SEY of Cu samples with different oxidation states, obtained either through laser treatment in air or in different gas atmospheres or via thermal annealing, has been measured at room and cryogenic temperatures and correlated with the surface composition measured by x-ray photoelectron spectroscopy. It was observed that samples treated in nitrogen display the lowest and more stable SEY values, correlated with the lower surface oxidation. In addition, the surface oxide layer of air-treated samples charges upon electron exposure at a low temperature, leading to fluctuations in the SEY.

The influence of microgeometries on the Secondary Electron Yield (SEY) of surfaces is investigated. Laser written structures of different aspect ratio (height to width) on a copper surface tuned the SEY of the surface and reduced its value to less than unity. The aspect ratio of microstructures was methodically controlled by varying the laser parameters. The results obtained corroborate a recent theoretical model of SEY reduction as a function of the aspect ratio of microstructures. Nanostructures - which are formed inside the microstructures during the interaction with the laser beam - provided further reduction in SEY comparable to that obtained in the simulation of structures which were coated with an absorptive layer suppressing secondary electron emission.

Secondary Electron Yield (SEY) [3, 5] occurs in a system when a primary electron impinges a material's surface and induces the emission of a 1 st and potentially 2 nd generation secondary electrons (see Figure 1, Left). The total number of secondary electrons per primary electron is the SEY. This phenomenon fonns a highly challenging problem in many systems, for example in particle accelerators, where significant levels of SEY fonn as an electron cloud and can perturbate the circulating beams and generate a high level of heat load to be absorbed by cooling and cryogenics. The Large Hadron Collider (LHC) lias a 54-km beam pipe [1] in which copper-laminated steel beam-screens are placed in order to shield the beam pipes from heat loads, but inherently result in unwanted SEY. As such, the development of methods which mitigate the SEY are increasingly appealing [2], including surface texturing, shaping the geometry and orientation of patterns etched into the surfaces [3], and carbon-coating of the interior of the beam pipes in the Super Proton Synchrotron (SPS) [4], Previously we have shown that nanosecond pulsed laser treatment of copper surfaces at 532 mn could significantly increase the optical absorbance of the surface [6], and furthennore reduce the SEY to close to 1 [7], More recently we demonstrated that surface structures produced by a picosecond pulsed laser at 532mn exhibited SEY values below 1 and were successfully tested in a dipole magnet in the Super Proton Synchrotron (SPS) accelerator at CERN [8].

Electron multipacting and electron cloud have been identified as being the major limiting factors for the beam quality or for the cryogenic system of high-intensity positive particles accelerators. Among conditioning operational techniques and other surface structuration techniques used to decrease the Secondary Electron Yield (SEY) of surfaces, laser surface treatment is a promising method to treat in situ and at atmospheric pressure copper surface of the vacuum chamber. Here, pulsed laser irradiation of copper in parallel lines pattern led to the local ablation and deposition of aggregates of copper particulates on the surface. Tests undertaken at CERN have shown that the modification of the surface morphology by creating roughness at different scales induces a decrease of the SEY by geometrical effects. Nevertheless, the mechanical strength and dust generation of the treated surface have not been addressed yet.In this work, a qualitative analysis of the multi-scale description of the surface morphology was carried out. Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to investigate morphological characterization such as size and shape of the particulates, chemical composition, metallographic structures and phase transformation on the laser-processed surface.SEM and FIB examinations showed that the surface morphology depends on the local laser energy irradiating the surface and especially, relatively to the ablation threshold. TEM analysis revealed chemical composition and crystalline configuration of the treated material and helped to identify the laser modified and oxidized areas. A variety of superficial structures were observed. Potential vulnerable structures have been identified as oxidized matter redeposited on the ablated near surface. Material continuity and composition play a major role in the mechanical integrity of the generated surface morphology. The adherence of the created structures was assessed analyzing the origin of the dust extracted after mechanical stress.

The surface resistance of copper samples with an amorphous carbon (a-C) coating or with laser surface structuring, the surface treatments of choice for electron cloud suppression in critical cryogenic sectors of the high-luminosity upgrade of the Large Hadron Collider (HL-LHC), has been measured for the first time at a cryogenic temperature using the quadrupole resonator at CERN. Three different frequencies of relevance for evaluating beam impedance effects, namely, 400, 800, and 1200 MHz, have been investigated. No significant increase in surface resistance is observed for the a-C coating, compared to plain copper. In the case of laser structuring, the surface resistance depends on the direction of the surface currents relative to the laser-engraved groove pattern. The increase is minimal for parallel patterns, but in the perpendicular case the surface resistance increases considerably. Radio frequency (rf) heating from wake losses would then also increase in the HL-LHC case; however, the reduction in the power deposited onto the cold surfaces thanks to electron cloud suppression would still outweigh this effect.