Improving light output and coincidence time resolution of scintillating crystals using nanoimprinted photonic crystal slabs

Pots, Rosalinde; Salomoni, Matteo; Gundacker, S.; Zanettini, Silvia; Gâté, Valentin; Usureau, Elise; Turover, Daniel; Lecoq, P.; Auffray, E.

doi:10.1016/j.nima.2019.06.026

Cited by 17 publications

(16 citation statements)

References 9 publications

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“…Indeed, from measurements performed on our air-coupled samples with Teflon wrapping we observed an improvement of ∼25% and ∼15% in energy resolution and ∼50% and ∼30% in light gain for LYSO and BGO, respectively. In this case, the gain provided by the PhC coating, without employing optical coupling compounds, was in line with what reported in the literature [17][18][19][20][21][22]26].…”

Section: Discussionsupporting

confidence: 91%

“…These structures rely on a high refractive index contrast between the nanostructure and the surrounding medium, leading to interesting optical properties especially if applied on the surface of high refractive index material. Indeed, PhCs have shown to be capable of increasing the amount of light extracted from inorganic scintillators, albeit to varying degrees and under often quite different experimental conditions, such as for LSO [17], LYSO [19][20][21][22] (self-assembly and e-beam, and nanoimprint), GYGAG and SrI 2 [23] (nanoimprint), CsI(Na) [24,25], and BGO [26] (self-assembly). A more comprehensive description of the PhC physics is reported in [17,18].…”

Section: Novel Light Extraction Enhancement Techniquesmentioning

confidence: 99%

“…However, the PhC structures have been mostly optimized and tested using air coupling with the photodetector optical window [21], in some cases with techniques that do not scale to large patterning areas. In addition, their structure is very fragile and not suitable to be used easily and reliably in standard configurations, in which a refractive index matching compound is employed between the crystal and sensor optical window.…”

Section: Novel Light Extraction Enhancement Techniquesmentioning

confidence: 99%

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Light Extraction Enhancement Techniques for Inorganic Scintillators

et al. 2021

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Scintillators play a key role in the detection chain of several applications which rely on the use of ionizing radiation, and it is often mandatory to extract and detect the generated scintillation light as efficiently as possible. Typical inorganic scintillators do however feature a high index of refraction, which impacts light extraction efficiency in a negative way. Furthermore, several applications such as preclinical Positron Emission Tomography (PET) rely on pixelated scintillators with small pitch. In this case, applying reflectors on the crystal pixel surface, as done conventionally, can have a dramatic impact of the packing fraction and thus the overall system sensitivity. This paper presents a study on light extraction techniques, as well as combinations thereof, for two of the most used inorganic scintillators (LYSO and BGO). Novel approaches, employing Distributed Bragg Reflectors (DBRs), metal coatings, and a modified Photonic Crystal (PhC) structure, are described in detail and compared with commonly used techniques. The nanostructure of the PhC is surrounded by a hybrid organic/inorganic silica sol-gel buffer layer which ensures robustness while maintaining its performance unchanged. We observed in particular a maximum light gain of about 41% on light extraction and 21% on energy resolution for BGO, a scintillator which has gained interest in the recent past due to its prompt Cherenkov component and lower cost.

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Section: Discussionsupporting

confidence: 91%

Section: Novel Light Extraction Enhancement Techniquesmentioning

confidence: 99%

Section: Novel Light Extraction Enhancement Techniquesmentioning

confidence: 99%

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Light Extraction Enhancement Techniques for Inorganic Scintillators

et al. 2021

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“…The next steps concerning the PhC will consist in extending the experimental characterization to crystal needles as well as measuring the possible impact of the PhC on the spatial reconstruction on one side, and the temporal on the other in terms of timing performance. We expect an improvement of CRT as also suggested in [17,20,35,36]. Another interesting, though challenging perspective is represented by the simulation of the light interaction with the entire scintillator-photodetector interface and the scintillating crystal itself, to optimize the output gain.…”

Section: Discussionmentioning

confidence: 70%

“…However, the PhC structures have been mostly optimized and tested using air coupling with the photodetector optical window [20], in some cases with techniques that do not scale to large patterning areas. In addition, their structure is very fragile and not suitable to be used easily and reliably in standard configurations, in which a refractive index matching compound is employed between the crystal and the sensor optical window.…”

Section: Novel Light Extraction Enhancement Techniquesmentioning

confidence: 99%

Light Extraction Enhancement Techniques for Inorganic Scintillators

Gramuglia¹,

Frasca²,

Ripiccini³

et al. 2021

Preprint

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Scintillators play a key role in the detection chain of several applications which rely on the use of ionizing radiation, and it is often mandatory to extract and detect the generated scintillation light as efficiently as possible. In positron emission tomography (PET), for example, both energy resolution and coincidence resolving time, two of the key detection parameters, depend strongly on the total amount of light which reaches the photodetector surface as well as its spatial and temporal distribution. Typical inorganic scintillators do however feature a high index of refraction, which impacts light extraction efficiency in a negative way. Furthermore, several applications such as preclinical PET rely on pixelated scintillators with small pitch. In this case, applying reflectors on the crystal pixel surface, as done conventionally, can have a dramatic impact of the packing fraction and thus the overall system sensitivity. This paper presents a study on light extraction techniques, as well as combinations thereof, for two of the most used inorganic scintillators (LYSO and BGO). Novel approaches, employing distributed Bragg reflectors (DBRs), metal coatings, and a modified Photonic Crystal (PhC) structure, are described in detail and compared with commonly used techniques. The nanostructure of the PhC is surrounded by a hybrid organic/inorganic silica sol-gel buffer layer which ensures robustness while maintaining its performance unchanged. We observed in particular a maximum light gain of about 41% on light extraction and 21% on energy resolution for BGO, a scintillator which has gained interest in the recent past due to its prompt Cherenkov component and lower cost.

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Monolithic Integration of Metalens in Silicon Photomultiplier for Improved Photodetection Efficiency

Uenoyama¹,

Ota²

2022

Advanced Optical Materials

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Improving the SiPM performance, such as photon detection efficiency (PDE) and timing resolution, is key to high-accuracy measurements for these applications.A SiPM typically contains trench areas, which are located between the boundaries surrounding SPADs, to shield from optical crosstalk. However, trenches can be photo-insensitive areas. Thus, incident photons impinging the trench areas cause PDE degradation. To solve this problem, microlenses are commonly integrated with SPADs to guide the incident photons toward their photosensitive area. [10,11] The recent trend toward miniaturization of the SPAD has led to the development of a complex photosensitive area because electrode patterns and trench areas must be formed in a limited space. However, the fabrication of complex-shaped microlenses has been challenging. Furthermore, precise alignment between microlenses and small state-of-the-art SPADs has been technically difficult because microlenses are incompatible with the CMOS process.On the other hand, metalenses, [12][13][14][15][16][17][18] such as 2D sub-wavelength structures, are highly flexible in shape and size, and can be designed to focus incident photons on the complex and small photosensitive areas of SPADs. [19,20] In addition, metalenses can be easily integrated with such SPADs without alignment errors owing to their 2D ultrathin structure and suitability for CMOS processes. Based on these advantages, we introduce a monolithic metalens integrated with SPAD rather than using microlenses.Our previous study demonstrated that metalenses can improve the PDE and timing performance of the SiPM by focusing the incident photons toward the photosensitive area of the SPAD while avoiding illumination to the trench area. [21] However, as the metalens and SiPM are spatially separated, it is difficult to fix the relative position (e.g., tilt, distance, and alignment) between the metalens and the SiPM. Thus, a separate configuration is not practical. A metalens should be monolithically integrated with its corresponding SPAD to provide good alignment and stable performance enhancement while maintaining the miniaturization and flatness of the optical device, which benefits practical applications.A 300-µm-thick support glass or protection resin is typically mounted on a SiPM to protect its surface. [22] However, when metalenses are formed on the support glass, the propagation Silicon photomultipliers (SiPMs), consisting of 2D single-photon avalanche diode (SPAD) arrays, have been widely used in many applications. In a SiPM, trench structures surround every SPAD to minimize optical crosstalk; however, these structures are photo-insensitive areas. The previous study revealed that the use of metalenses for focusing incident photons on the photosensitive area of SPADs effectively improves the SiPM performance. However, ensuring good alignment between the metalens and SiPM has been difficult owing to its separated configuration. Herein the authors report the monolithic integration of a metalens with SPAD to provide stable pho...

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Improving light output and coincidence time resolution of scintillating crystals using nanoimprinted photonic crystal slabs

Cited by 17 publications

References 9 publications

Light Extraction Enhancement Techniques for Inorganic Scintillators

Light Extraction Enhancement Techniques for Inorganic Scintillators

Light Extraction Enhancement Techniques for Inorganic Scintillators

Monolithic Integration of Metalens in Silicon Photomultiplier for Improved Photodetection Efficiency

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