Deep tech companies – from photonics and semiconductors to quantum systems and advanced sensing – are among the most technically demanding in the STEM industries. Yet they remain among the least diverse corners of the modern workforce. Globally, women represent less than a third of the STEM workforce, compared with nearly half of workers in non-STEM roles, and the proportion drops further in engineering-heavy domains that underpin deep tech. For example, In the UK semiconductor industry, women account for only 26% of employees and just 18% in technical roles.
But while many deep tech organizations continue to struggle with representation, a new generation of startups is beginning to demonstrate that a more diverse workplace can drive a host of benefits, and Singular Photonics is one of them. The image sensor startup recently passed a significant milestone for a technology venture, announcing the first commercial deployment of its technology: a Raman spectroscopy collaboration with global instrumentation giant Renishaw. Unusually for a deep tech company, Singular has a high degree of ethnic and gender diversity in its workforce, particularly in its engineering team, which currently has a 50/50 mix of male and female employees.
Singular CEO Shahida Imani has always believed that diversity isn’t about hitting numbers.
“It’s about creating an environment where people feel trusted, free to think independently, and confident that their ideas will be heard,” she says. “When those conditions exist, talented people from many different backgrounds want to be part of the journey – and that benefits the organisation enormously.”
For many employees at Singular, the lack of diversity in deep tech is a lived experience. Firmware engineer Dr. Yuanyaun Hua recalls that in previous engineering roles, teams were around 90–95% men. “In a group I often used to be the only female, but now at Singular, it’s more balanced,” she says.
Having spent most of her career in academia, Senior Optical Scientist and Applications Engineer Dr. Katjana Ehrlich echoes Hua’s sentiment.
“Working in physics, often I was the only woman in the room,” she says. “I love physics, and I’ve always loved my work, even when it was challenging. As a woman, you often have to work harder, do more extracurricular activities, and make yourself visible, yet still might be overlooked.”
These experiences mirror broader trends across the sector. Hardware-focused environments have historically attracted and retained a narrower demographic profile than software-centric fields, reinforcing a cycle in which homogeneity becomes self-perpetuating.
“From my experience in every organization I’ve worked with – whether a small company, a large organization, or an academic environment – engineering fields like electrical, electronics, computer science, and optics are dominated by men,” says Singular co-founder and CTO Dr. Aravind Venugopalan. “That’s why I’m actually very proud of what’s happening at Singular. If you look at similar deep tech or photonics companies, you probably won’t find the same gender ratio we have.”
Senior Software Developer Shu Chen believes that deep tech companies are missing out on valuable talent if their workforce has limited female representation.
“In tech, many women leave the field due to discrimination, harassment, or lack of role models,” he explains. “The women who stay are often exceptionally strong because they’ve had to overcome more barriers. In that sense, companies are doubly losing out by excluding them.”
At Singular, diversity is far from a numbers exercise. Hiring decisions are based on capability and fit rather than demographic targets, yet the result has still produced a team that is unusually balanced for a deep tech startup.
“When I first met the whole company at a planning day, I was struck by how diverse the team was,” says Software Engineer Matthew Coady. “In many workplaces, people tend to look or think similarly, which becomes part of the culture. At Singular, it felt like everyone was genuinely different – and that felt like a good sign.”
Hua concurs, noting Singular’s diversified environment in terms of nationality, race, and gender.
“I feel quite relaxed and comfortable because everybody is from different backgrounds and different countries,” she says. “There isn’t one dominant group. That makes it easier to communicate with people.”
The importance of mutual respect and effective communication in a startup cannot be understated and Ehrlich believes the environment at Singular is conducive to innovation.
“At Singular, I felt very welcome from the start, there’s good communication, a positive working environment, and plenty of opportunities – I’m very happy here,” says Ehrlich. “My role gives me a lot of freedom to both build things up and explore what could be new and interesting applications.”
“At Singular, there’s more openness to ideas, and I noticed from my very first meeting that discussions were open and democratic – everyone contributed and was listened to,” agrees Coady. “I also noticed how self-organizing the team is. People don’t need to be told what to do; they just coordinate naturally and make time to listen to each other.”
While skill and expertise remain the most critical drivers of success in any team, many of Singular’s employees point to an indirect but powerful effect of diversity: to create conditions where people feel respected and therefore more willing to contribute.
“It brings different ideas,” says Venugopalan. “People think in different ways. It’s a bit like combining different sets of data – the more diverse they are, the richer the result. Everyone at Singular has a different background and story. My experience is not the same as someone else’s, and when you bring those different perspectives together, you get better outcomes. Instead of having ten people with the same story, it’s better to have ten people with different stories who can bring different perspectives.”
“I feel like I get the respect and I appreciate that, and that makes me want to contribute more,” agrees Hua. “Here at Singular, I feel relaxed to do whatever I can. That makes a big difference.”
For deep tech, the implications of diversity are strategic as much as ethical, and Chen also highlights the importance of domain diversity in creating competitive advantage.
“Singular benefits from technical diversity,” he says. “I came from a software startup background with no hardware experience, but I brought practices around building stable software, rapid iteration, and moving from prototype to production. Meanwhile, colleagues from academia bring rigor, careful experimentation, and deep engagement with research. That mix of startup speed and academic depth is very powerful.”
“In deep tech, we’re trying to solve very hard problems,” says Venugopalan. “If everyone thinks the same way, you might still reach a solution, but it will likely take longer and require more effort. With diverse perspectives, solutions often emerge faster. We see this every day at Singular.”
But diversity does not in itself guarantee a harmonious working environment, and Singular’s first employee, Senior Manufacturing and Application Specialist Mark Mooney, says the company’s success in this area is down to one main factor: empathy.
“If senior management have empathy-driven core values, everything flows from that – it’s that simple,” he says. “If your leadership values empathy, fairness and respect, then naturally you’ll hire people based on their talent and personality rather than their background. You’re not ticking diversity boxes – you’re simply selecting the best people who fit the team. That naturally leads to a diverse workplace.”
The broader deep tech sector still has a long road ahead. At current rates, equal gender representation across STEM fields may not arrive until around 2070 – a timeline that underscores how slow progress has been despite decades of conversation.
“I think it’s an open secret that the playing field isn’t level, and there’s still a long way to go before equality,” says Ehrlich. “I would still encourage anyone – especially women – to pursue what they want, even though I know it can be tough.”
“Tech companies are missing huge amounts of talent because their hiring systems are biased,” says Chen. “If 99% of applicants are men in a world that’s 50% women, something is wrong with the recruitment process – job adverts, outreach, or evaluation criteria.”
Despite the challenges facing the industry Singular’s experience so far suggests that startups have the opportunity to adopt a different trajectory. By building a culture where no single group dominates and where collaboration emerges naturally from varied backgrounds, the company is demonstrating that diversity can evolve organically without compromising technical excellence.
“I see diversity as a cultural thing that grows organically rather than something you can enforce through policies,” agrees Coady. “I think Singular’s culture needs to be nurtured day by day. If growth is gradual and people are mindful of preserving what makes the culture healthy, it should be possible to maintain it.”
According to Mooney, maintaining the culture as the Singular grows will come down to strong leadership.
“Right now the structure is simple, but as companies grow you introduce more layers of management,” he says. “That means group leaders and mid-level managers also need to embody those same values and pass them down to their teams. Of course, challenges will come as the company grows – the more people you hire, the more potential there is for culture clashes. But as long as we keep reinforcing those core values, I think we’ll be okay.”
“We never set out with a strict plan to engineer a specific demographic mix, yet it happened naturally,” adds Venugopalan. “We’ve been fortunate to meet resourceful, supportive people who wanted to join the team. I think that will continue.”
“In the earliest stages of a deep tech startup, you’re not just building a product – you’re building a culture,” concludes Imani. “If you build a culture based on trust, empathy and respect from day one, diversity isn’t something you have to force – it becomes a natural outcome of simply hiring the best people. The decisions you make about how people treat each other, how ideas are shared, and how problems are solved become the blueprint for everything that follows. If those foundations are built on empathy and fairness, the team becomes stronger, more creative and more resilient.”
Independent audit by BSI confirms imaging firm’s commitment to quality and customer satisfaction
Edinburgh, UK – February 25, 2026 – Image-sensor innovator Singular Photonics today announced it has achieved ISO 9001 certification, an internationally recognized standard for quality management systems. The certification reflects the company’s ongoing commitment to operational excellence, continuous improvement, and delivering reliable, high-performance image sensor solutions to customers worldwide.
ISO 9001 certification validates that Singular has implemented rigorous processes and quality controls across its design, development, manufacturing, and customer support operations. The certification was awarded following an independent audit conducted by BSI, the UK’s National Standards Body, confirming compliance with globally accepted best practices for quality management.
“Achieving ISO 9001 certification marks an important milestone in our development,” said Shahida Imani, CEO of Singular Photonics. “As demand grows for SPAD-based image sensors in applications spanning almost every market sector, customers rightly expect consistent quality, traceability, and reliability. This certification reinforces our commitment to exceeding those expectations.”
The ISO 9001 framework supports enhanced risk management, improved operational efficiency, and stronger alignment with customer requirements. For its partners and customers, the certification provides assurance that Singular maintains structured processes designed to deliver dependable products and responsive service.
Strategic collaboration integrates next-generation SPAD-based image sensor into Renishaw’s new Raman spectroscopy module to allow measurements of highly fluorescent samples
Edinburgh, UK – December 17, 2025 – Image-sensor innovator Singular Photonics today announced a major milestone in its strategic collaboration with Renishaw, a global leader in metrology and analytical instrumentation. The companies have been co-developing next-generation spectroscopy capabilities powered by Singular’s new suite of single-photon avalanche diode (SPAD) image sensors.
Renishaw today revealed the launch of its latest breakthrough in Raman spectroscopy: the addition of Time-Resolved Raman Spectroscopy (TRRS) to its renowned inVia™ confocal Raman microscope. At the core of this innovation is Singular’s Sirona SPAD sensor, enabling researchers and engineers to overcome one of Raman spectroscopy’s most persistent challenges – capturing Raman signals obscured by intense fluorescence backgrounds. With TRRS and Sirona, inVia users can now acquire high-quality Raman spectra from samples previously considered too difficult or impossible to measure.
“We are always on the lookout for new, innovative technology to maintain our lead in this market, and we believe we have achieved this with our partnership with Singular Photonics,” said Dr Tim Batten, Director and General Manager, Spectroscopy Products Division, Renishaw. “Our TRRS solution for the inVia microscope offers customers a multitude of benefits when dealing with highly fluorescent samples, such as those containing pigments. We have had an in-depth collaboration with Singular Photonics dating back to their inception and have been developing this product in tandem with their cutting-edge Sirona SPAD sensor.”
Built on advanced CMOS SPAD architecture, Singular’s Sirona is a 512-pixel SPAD-based line sensor integrating on-chip time-resolved processing and histogramming functionality. This allows simultaneous acquisition of both fluorescence and Raman signals with high temporal precision, unlocking new measurement modalities for scientific and industrial applications.
“By integrating the Sirona sensor into Renishaw’s new TRRS system, they have created a spectrometer that showcases the clear performance advantages of our SPAD technology,” said Shahida Imani, CEO of Singular Photonics. “We’ve built a strong relationship with the Renishaw team since before our spin-out from the University of Edinburgh, fostering trust and deep technical collaboration. This partnership opens a significant opportunity to expand our market reach, especially in high-precision scientific and industrial sectors.”
Fast-growing fabless semiconductor start-up welcomes Richard Lochhead to its headquarters at the Royal Observatory in Edinburgh.
Singular Photonics today welcomed Richard Lochhead, Minister for Business and Employment, to its headquarters at the Royal Observatory in Edinburgh. Founded just 18 months ago, the company is already generating revenue and developing world-leading sensor technology, cementing its position as one of Scotland’s most exciting new deep-tech ventures.
Single-photon avalanche diodes (SPADs) are transforming how machines capture and interpret the world around them. Singular Photonics is at the forefront of this shift, focusing on pushing SPAD technology into practical, high-impact applications, including biomedical imaging, industrial automation, scientific, and quantum technologies.
Mr Lochhead met the leadership team and joined a roundtable discussion on the future of Scotland’s critical technologies supercluster. Topics included building the right environment for scale-up companies and attracting international investment to Scotland.
“Singular Photonics is a shining example of Scotland’s innovation potential,” said Shahida Imani, co-founder and CEO. “Our progress reflects the strength of our team and Scotland’s ability to nurture world-class deep tech companies.”
“It is inspiring to see a young Scottish company like Singular Photonics achieving so much in such a short space of time,” said Mr Lochhead. “Its success underlines the strength of Scotland’s deep-tech ecosystem and shows the potential we have to create high-value jobs and attract global investment. Supporting innovative businesses is central to our ambition of growing Scotland’s critical technologies supercluster and strengthening our economy for the future.”
“Later this month we will staging Scotland’s first National Innovation Week and Singular Photonics is developing the kind of sector-leading technology that we will be highlighting to a global audience.”
The visit concluded with official photographs alongside the founders and investors, reinforcing Scotland’s commitment to supporting innovation-driven scale-ups.
Real-time blood flow monitoring with the Andarta SPAD sensor.
At this year’s Laser World of Photonics in Munich, Singular Photonics debuted a live demonstration of a breakthrough in non-invasive blood flow monitoring. The demo showcased how our Andarta sensor performs real-time Diffuse Correlation Spectroscopy (DCS) to detect blood flow changes through tissue — all without a single needle, contact pad, or delay. Just light, computation, and physiology in action.
The live setup demonstrated how the sensor captures real-time microvascular dynamics — tracking pulsatile blood flow at the fingertip in real time and resolving subtle changes in perfusion with high temporal resolution. Processing is performed on-chip, with real-time autocorrelation computation of blood cell motion.
This demo was more than a technical proof point. It provided a glimpse into the future of contactless, clinically relevant sensing — one that could influence healthcare, industrial process monitoring, and beyond.
A New Era of Optical Sensing
The demo was powered by our Andarta sensor, a 512×512 SPAD (single-photon avalanche diode) array built using 3D-stacked backside-illuminated (BSI) CMOS technology. The Andarta sensor represents a significant leap in the evolution of SPAD-based imaging, combining cutting-edge 3D-stacked CMOS technology with real-time data processing embedded directly on the chip.
Unlike conventional systems that record photon data and rely on external computing to process it, Andarta performs in-pixel, on-chip autocorrelation calculations using a densely parallel 128×128 macropixel architecture. This enables the device to resolve physiological signals such as blood flow dynamics — and even subtle cardiac pulsations — with lag-times under 1 microsecond.
The benefits go far beyond speed. The sensor performs 0.5 trillion operations per second while consuming just 0.3 watts of power, all within a compact footprint. It’s not just fast — it’s portable, efficient, and scalable.
This makes Andarta an enabling platform not only for biomedical monitoring but for real-time analytics in pharma, clean energy, agritech, and other domains where understanding flow at the micro level matters.
Technical info
Andarta combines a high fill-factor BSI SPAD layer — optimized for photon detection sensitivity — with a deeply integrated logic layer beneath, enabling true in-pixel processing at scale. This vertically stacked architecture allows each of the 128×128 macropixels to compute photon correlation functions in real time, eliminating the need for off-chip post-processing. The result is a low-power, high-speed sensing platform capable of resolving blood flow dynamics with sub-microsecond resolution and exceptional signal-to-noise performance.
With over 120 million transistors on-chip and throughput reaching 0.5 trillion multiply-accumulate operations per second (MAC/s) — all within a compact, 0.3 W envelope — Andarta brings data-rich, non-contact physiological measurement into a new era of portability and embedded intelligence.
Strategic collaboration will see AMS distribute Singular’s computational image sensors across European markets and industries.
Edinburgh, UK – June 13, 2025 – Singular Photonics, a pioneer in image sensor technologies, today announced a strategic partnership with AMS Technologies, Europe’s leading distributor and solution provider for optical technologies. The partnership will bring Singular’s next generation image sensors based on single photon avalanche diodes (SPADs) to customers in key European markets and industry sectors.
The collaboration means that AMS becomes Singular’s distribution and support partner for the European market. With decades of experience in photonics, AMS will leverage its extensive sales network and trusted industry reputation to deliver Singular’s breakthrough SPAD technologies to OEMs, research labs, and system integrators across Europe.
Singular is one of the first companies to bring advanced on-chip computation to SPAD-based image sensing. The company’s advanced single-photon detection technology enables the extraction of significantly more information from light by leveraging real-time processing of photon-level signals. This unlocks groundbreaking new capabilities across a range of fields, including:
The companies’ first engagement together will be at next week’s Laser World of Photonics in Munich, where Singular’s sensors will be demonstrated on the AMS Technologies stand (B2.203).
“Partnering with AMS Technologies is a pivotal moment in our growth and marks a major step toward global commercialisation of our sensors,” said Shahida Imani, CEO at Singular Photonics. “Our SPAD sensors are enabling entirely new imaging applications across many fields, and AMS’s deep market knowledge, customer relationships and trusted support infrastructure will be invaluable in bringing these innovations to European partners.”
“The demand for single-photon sensing is growing rapidly in a wide range of sectors, and Singular Photonics is at the forefront of the latest developments in this exciting area,” said Jan Meise, CEO of AMS Technologies. “With distribution, engineering, and production under one roof, we can’t wait to help Singular accelerate their growth in key markets.”
We are delighted to announce that Singular Photonics has achieved a significant milestone by receiving CE mark certification for our advanced SPAD-based image sensing products, including our Sirona and Andarta sensors.
Securing this certification is a crucial external validation of our technology and allows us to commercialize our sensors within the European Economic Area (EEA). The CE mark signifies that Singular Photonics’ products meet the stringent safety, health, and environmental protection standards required by the European Union, enabling them to be sold freely across the EEA without additional regulatory barriers.
Achieving CE mark status underscores our commitment to product safety and regulatory compliance. By obtaining this certification, we are showing that we take our responsibilities seriously, ensuring that our SPAD-based sensors adhere to the highest standards of quality and reliability. This is particularly important in our work with original equipment manufacturer (OEM) customers – including some of the world’s largest and most demanding electronics equipment companies – who expect nothing less of their suppliers than full compliance with international standards.
“Securing the CE mark is more than just a regulatory requirement; it is a strategic asset,” said our CEO, Shahida Imani. “It not only facilitates seamless market access across 33 countries in the EEA but also boosts our credibility and competitiveness in a key emerging market. The certification will simplify trade processes, reduce liability risks, and enhance confidence in the safety and efficacy of our products.”
Startup introduces range of sensors with layers of advanced computation to extract valuable information from images.
Edinburgh, UK – January 23, 2025 – Singular Photonics emerged from stealth mode today, launching a new generation of image sensors based on single photon avalanche diodes (SPADs). A spin-out from the University of Edinburgh lab of digital imaging pioneer Professor Robert Henderson, Singular is one of the first companies to bring advanced computation to SPAD-based image sensing, enabling in-pixel and cross-pixel storage and computations at the lowest light levels to reveal previously invisible details of the material world and its photon events.
The company will showcase its products for the first time at next week’s SPIE Photonics West event in San Francisco.
SPADs use the “avalanche” effect in semiconductors to convert light directly into an electrical current, without the need for cooling or amplification. While most commercial SPAD-based image sensors have been limited to time-resolved counting of photons, Singular’s core innovation lies in complex layers of computation beneath 3D-stacked SPAD sensors, comparable to the way FPGAs and GPUs revolutionized parallel computing by conducting high-speed, localized processing.
Prof Henderson leads the University of Edinburgh’s CMOS Sensors and Systems Group. In 2005, he designed one of the first SPAD image sensors in nanometer CMOS technologies, leading to the first time-of-flight sensors in 2013, which today perform an autofocus-assist feature in more than a billion smartphones worldwide.
“There can be no doubt that SPAD sensors are the future of digital imaging, but their use to date in commercial devices hasn’t extended much beyond time-resolved counting of photons,” said Prof Henderson. “Computational cleverness can be the difference. We are building next-generation imaging sensors, where the computation is done digitally at the pixel level – exactly where the photons arrive.”
Simultaneously capturing depth and temporal dimensions to generate 4D images that provide deep, data-rich insights, Singular’s noiseless sensors enable more information to be extracted from light, supporting applications ranging from consumer and automotive electronics to the scientific and medical fields. The company’s approach transforms SPAD sensors into 3D stacked computational engines capable of performing a wide range of sophisticated tasks, such as real-time photon counting, timing, and advanced processing techniques, including in-pixel histograms, statistical analysis and autocorrelation.
Singular is launching with two sensors, both of which are available today:
Singular has already inked multiple deals for its sensors with some of the world’s leading instrumentation companies, and expects to announce more collaborations in 2025.
“We are in a unique position where we already have commercially available products and are generating revenue in our first year of incorporation,” said Shahida Imani, CEO of Singular Photonics. “With new, even more advanced sensors coming to the market in 2025, we are well positioned to lead the SPAD-driven imaging revolution.”
Introduction
The Andarta Sensor from Singular Photonics is a 512×512 single-photon avalanche diode (SPAD) array (Gorman, 2024). Incorporating several photon acquisition modes implemented in the latest 3D-stacked CMOS technology, a stand-out feature of Andarta is support for diffuse correlation spectroscopy (DCS) in ensemble and imaging configurations. Andarta DCS characterises motion of scattering particles such as red blood cells in tissue, e.g. for cerebral blood flow monitoring applications, providing important indicators of brain health. Configured in a 128×128 macropixel format, highly parallel in-pixel autocorrelation computation is supported, with a minimum autocorrelation lag-time less than 1 μs. As a result, Andarta can resolve changes in body tissue decorrelation in real time, at the longest source-detector separations achieved by the current leading optical modalities for cerebral blood flow monitoring.
In this Research Highlight we report the work of Prof. Robert Henderson (Chief Scientist at Singular Photonics), Dr. Alistair Gorman and colleagues at the Institute for Integrated Micro and Nano Systems, University of Edinburgh to characterise direct, on-chip computation of the autocorrelation function of the Andarta sensor. Suitability for in-vivo data acquisition is illustrated with cuff-occlusion measurements.
Materials and Methods
The Andarta sensor uses advanced 3D-stacked backside illuminated (BSI) SPAD technology to provide enhancements in detection efficiency and to enable densely populated logic layers to deliver embedded pixel-parallel computation of autocorrelation. The entire macropixel array employs 120 M transistors, supports 0.5 T MAC operations per second (Op/s) and consumes around 0.3 W power.
Andarta macropixels calculate autocorrelation components directly during each integration cycle, rather than streaming photon-counting frames for off-pixel autocorrelation computations. Averaging of individual macropixel autocorrelations is supported in an on-chip, high-speed “ensemble” mode yielding strong signal-to-noise-enhancement for multispeckle DCS applications.
Optical System
The optical setup used for diffuse correlation spectroscopy with the Andarta SPAD sensor is shown in Fig. 1. A stabilized laser diode (Thorlabs LP785-SAV50) is driven in continuous wave mode. The laser is collimated and attenuated as necessary. Light transmitted through the sample is collected with a fiber bundle, consisting of seven 550-μm core multimode fibers, and relayed to the Andarta detector array.
Fig. 1 Optical Setup for Diffuse Correlation Spectroscopy (Gorman et al 2024)
Diffuse Correlation Spectroscopy
Ensemble mode DCS measurements demonstrate the ability of the sensor to resolve changes in blood flow in cuff occlusion measurements. Cuff occlusion measurements are taken at the ulnar side of the left palm (Fig. 2(a)), with a laser to detection fiber separation of 40 mm. Measurements are taken during and after a gradual, approximately linear increase of occlusion pressure of the left wrist, starting at 0 mm Hg and reaching a maximum of pressure of 165 mm Hg at 40 s, at which point there is an abrupt decrease to 0 mm Hg.
Fig. 2 (a) Source and detection fiber at palm. (b) Time constant during and after a linear increase of wrist occlusion pressure from 0 mm Hg to a peak of 165 mm Hg at 40 s. (c) Six pulse periods of the time constant post occlusion. (Gorman et al 2024)
Figure 2(b) shows a plot of the time constant from exponential fitting of the autocorrelation values. The time series shows the characteristic post-occlusion reactive hyperemia (higher blood flow). Also shown in Fig. 2(c)) is an example of six periods of the pulse waveform post occlusion.
Measurements of cardiac signals from the forehead of an adult subject, diffuse correlation imagery and full details on the Andarta DCS performance can be found in the journal article (Gorman et al. 2024).
In-vivo DCS measurements demonstrates use of the Andarta sensor to show sensitivity to changes in blood flow. The ability to measure signals in tissue with large source-detector separations highlights the potential of this sensor for non-invasive monitoring of cerebral blood flow. In-pixel and on-chip real-time calculation of the autocorrelation function eliminates the need for post-processing, reduces computational burden and enables faster data acquisition rates. Tiling of Andarta arrays to further SNR improvements, and provision for simultaneous measurements at multiple locations is readily supported with our architecture. Compact size and low power consumption of Andarta make it an attractive option for wearable or portable devices.
The Engineering and Physical Sciences Research Council (EP/T020997/1) and Meta Platforms Inc. are thanked for funding this work.
This document “Diffuse Correlation Spectroscopy with the Andarta Sensor ” is adapted from (Gorman et al, 2024) and licensed under CC BY 4.0
Gorman, A., Finlayson, N., Erdogan, A. T., Fisher, L., Wang, Y., Mattioli Della Rocca, F., Mai, H., Sie, E. J., Marsili, F., & Henderson, R. K. (2024). ATLAS: a large array, on-chip compute SPAD camera for multispeckle diffuse correlation spectroscopy. Biomedical Optics Express, 15(11), 6499.
Introduction
Time-resolved Raman and fluorescence lifetime spectroscopy and imaging is a key application of single photon avalanche diode (SPAD) sensors (Finlayson et al. 2023). Raman photons typically arrive before fluorescence emission photons and these can therefore be distinguished from each other using time-resolved detection. New material research becomes possible as a result, in applications including biomedical diagnostics, quantum optics, carbon materials, and battery development. Here we describe time- resolved Raman spectroscopy and imaging using the Sirona sensor.
Materials and Methods
Sirona supports in-pixel CMOS construction of time-resolved spectral histograms in each of up to 1024 spectral channels, with up to 50ps time resolution. Photon arrival time events are recorded in every pixel histogram from the initial excitation of a laser excitation pulse to a time range extending from tens of picoseconds to hundreds of nanoseconds. Simultaneous acquisition of Raman and fluorescence signals are carried out in each spectral channel (Usai et al. 2019). Motorized and beam scanning microscopy systems can then be used to produce combined Raman and fluorescence images composed of highly detailed 4D data-cubes having two spatial dimensions, one spectral dimension and one time dimension.
The Sirona sensor is a CMOS Single Photon Avalanche Diode (SPAD) line sensor with per-pixel histogramming time-to-digital converters for time-resolved multispectral imaging. Shot-noise limited sensitivity, time-correlated single photon counting (TCSPC) functionality and room temperature operation set the Sirona SPAD sensor apart from CCD device technology. Extensive triggering options are available for integration with a range of scanning systems and laser sources. A delay generator with 63 ps time resolution and 8 configurable histogram time-ranges is included.
Optical System
The time-resolved optical microscope built around the Sirona SPAD sensor is shown in Fig. 1. A pulsed laser (typically NKT Katana, wavelength 532nm, pulse duration <50 ps, repetition rate 1-40 MHz, linewidth 0.15nm) is directed at the sample using a dichroic mirror. The laser beam incidence position on the sample can be changed using either a motorised stage or with scanning mirrors, producing an XY scan at an image plane at the back aperture of the primary objective.
Raman and fluorescence signals are transmitted back through the dichroic, through an ultra-steep long-pass emission filter and coupled to a custom f/1.5 spectrometer through a 10× 0.25NA microscope objective and 50 µm diameter fiber optic patch cable that acts as the system pinhole. Light emerging from the other end of this fiber is collimated with an achromatic doublet lens and then diffracted by an 1800 lp/mm transmissive holographic grating. Finally, the photons are focused using an achromatic doublet lens and collected by the CMOS SPAD line sensor. The spectrometer spectral range is approximately 80 nm, and the spectral resolution is approximately 0.16 nm.
Fig. 1 Optical Raman Microscope (Finlayson et al 2021)
Sesame Oil
In Fig. 2, we present a time-resolved spectrum of sesame oil. Raman and fluorescence signals are captured using an exposure time of 10 s. Known sesame oil Raman peaks at 1080, 1265, 1300, 1440, 1660, and 1750 cm−1 are visible, together with a broad fluorescence background with a lifetime estimated to be 2.7ns.
Fig. 2 Time-resolved Raman and fluorescence of sesame oil
Raman and Fluorescence Imaging
Raman imaging was investigated using mixed samples consisting of calcite and carbon single wall nanotubes (SWNT). Calcite has strong easily identifiable Raman lines, while carbon allotropes such as diamond, graphite and more unusual allotropes such as SWNT and graphene are materials of considerable interest with distinctive Raman signatures.
The SWNT sample was fabricated by high-pressure decomposition of carbon monoxide. Individual SWNT were found to have diameters in the range 0.7−1.4 nm. Raman spectra of SWNT demonstrate these typical labelled spectral features: SWNT diameter dependent radial breathing mode (RBM) in the range 150- 280 cm-1, the so-called D-line at 1350 cm-1, the G-line at 1585 cm-1 which splits into metallic (G-) and semiconducting (G+) species, and the G’-band at approx. 2700 cm-1.
The SWNT sample was overlaid onto a calcite background sample. The samples can readily be distinguished in these images through their distinctive time-separated Raman spectral features. In addition, highly fluorescent regions in the images can also be identified at later times, arising from defects.
The resulting time- resolved 64×64 pixel motorized scanner images are shown in Fig 3. A 6 frame time-sequence highlighting the SWNT region at a Raman wavenumber of 1585 cm-1 (the G+ line position) is shown in the top row. Each frame is separated by an interval of 100ps. A 6 frame time-resolved sequence highlighting the calcite region at a Raman wavenumber of 1086 cm-1 is shown in the bottom row. Both sequences highlight the growth of the Raman signals in the 0-200ps time range. It is important to note that both rows of images are subsets of a single time-resolved datacube. The calcite and SWNT regions are strongly differentiated through their distinctive Raman signatures, lighting up or essentially invisible at quite distinct wavenumbers.
Fig. 3 Time-resolved Raman and fluorescence images of calcite and carbon nanotubes. The frames in each sequence are obtained from successive 100ps histogram bins at two different wavenumbers. Top row: carbon single wall nanotube G+ image region at a wavenumber of 1585cm-1. Bottom row: calcite image region at 1086cm-1. Calcite, carbon nanotube and longer lived fluorescence regions are clearly distinguished (Finlayson et al 2023)
The capabilities of Sirona SPAD-based time-resolved Raman and fluorescence detection were highlighted in this note using oil, carbon and calcite samples. In-pixel photon timestamp histogramming in each spectral channel ensures that both Raman and fluorescence photon signatures are acquired simultaneously.
The Engineering and Physical Sciences Research Council (EPSRC, United Kingdom) Interdisciplinary Research Collaboration (grant number EP/K03197X/1 and EP/R005257/1) is thanked for funding this work.
This document ” Time-resolved Raman Spectroscopy and Imaging with the Sirona Sensor ” is adapted from (Usai et al, 2019; Finlayson et al, 2021; Finlayson et al 2023) and licensed under CC BY 4.0
Usai, A., Finlayson, N., Gregory, C. D., Campbell, C., & Henderson, R. K. (2019). Separating fluorescence from Raman spectra using a CMOS SPAD TCSPC line sensor for biomedical applications. In R. R. Alfano, S. G. Demos, & A. B. Seddon (Eds.), Optical Biopsy XVII: Toward Real-Time Spectroscopic Imaging and Diagnosis (Issue March 2019, p. 26). SPIE. https://doi.org/10.1117/12.2508459
Finlayson, N., Usai, A., Brown, G. E., McEwan, H., Erdogan, A. T., Campbell, C. J., & Henderson, R. K. (2021). Time-correlated single photon Raman spectroscopy at megahertz repetition rates. Optics Letters, 46(17), 4104. https://doi.org/10.1364/ol.434418
Finlayson, N., McEwan, H., Brown, G., Gorman, A., Gromov, A., Campbell, C., Erdogan, A., Henderson, R., & Williams, G. (2023). Time-correlated Raman imaging with a SPAD line sensor. In R. R. Alfano & A. B. Seddon (Eds.), Optical Biopsy XXI: Toward Real-Time Spectroscopic Imaging and Diagnosis (Vol. 1237302, Issue March, p. 7). SPIE. https://doi.org/10.1117/12.2648899
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