Optics Letters

Journal: Optics Letters

Abbreviation

Opt. Lett.

Publisher

Optica

ISSN

0146-9592
1539-4794

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Publications 1 - 10 of 18

Correcting for sub-resolution tissue motion in localization optoacoustic tomography
Zhao, Jim; Nozdriukhin, Daniil; Razansky, Daniel; et al. (2025)
Optics Letters
Localization optoacoustic tomography (LOT) has recently been suggested for enhancing spatial resolution in optoacoustic imaging beyond the acoustic diffraction barrier and further enabling measuring blood flow velocity. LOT relies on tracking highly absorbing particles in a sequence of images acquired following intravenous injection. Much like for other high-resolution imaging methods, the achievable resolution in vivo is afflicted by physiological motion. Inter-frame displacements further hamper particle tracking and accurate velocity measurements. Herein, we propose a geometric-transformation-based approach to align motion-affected frames to a reference frame. This is achieved with a singular value decomposition (SVD) clutter filter, clustering the acquired sequence into low-order singular vectors representing blood-vessel background and high-order singular values related to flowing particles. Motion estimation is then performed in the background sequence, and localization and tracking are subsequently done in the flowing-particle sequence after motion correction. The enhanced performance achieved with the suggested approach is demonstrated in phantom experiments and LOT images of the mouse brain.
Compact laser-diode-based optoacoustic mesoscopy
Liu, Xiang; Li, Weiye; Liu, Yu-Hang; et al. (2025)
Optics Letters
Short-pulsed solid-state lasers (SSLs) are the most commonly employed light sources in optoacoustic imaging applications. However, their bulky size hinders compact and portable system implementations. Here we developed a compact laser diode (LD)-based optoacoustic mesoscopy (CoLD-OAM) scanner that employs a fiber-coupled laser diode source with 46 × 43 × 11 mm dimensions. CoLD-OAM features a scalable excitation pulse width in the 30–200 ns range, high pulse energies up to 6 µJ, and excellent pulse-to-pulse energy stability of 0.42%. Real-time imaging of the human wrist has been demonstrated with the system, achieving image quality similar to that of SSL-based systems. These advancements facilitate the development of portable optoacoustic systems with strong clinical translation and commercialization potential.
Probing coherence Stokes parameters of three-component light with nanoscatterers
Guo, Mengwen; Norrman, Andreas; Friberg, Ari T.; et al. (2022)
Optics Letters
We establish a method to determine the spectral coherence Stokes parameters of a random three-component optical field via scattering by two dipolar nanoparticles. We show that measuring the intensity and polarization-state fringes of the scattered far field in three directions allows us to construct all nine coherence Stokes parameters at the dipoles. The method extends current nanoprobe techniques to detection of the spatial coherence of random light with arbitrary three-dimensional polarization structure.
Scan-less 3D microscopy based on spatiotemporal encoding on a single-cavity dual-comb laser
Lu, Wanping; Zhu, Zhiwei; Willenberg, Benjamin; et al. (2024)
Optics Letters
Dual-comb microscopy enables high-speed and high-precision optical sampling by simultaneously extracting both amplitude and phase information from the interference signals with frequency division multiplexing. In this Letter, we introduce a spatiotemporal encoding approach for dual-comb microscopy that overcomes previous limitations such as mechanical scanning, low sampling efficiency, and system complexity. By employing free-space angular-chirp-enhanced delay (FACED) and a low-noise single-cavity dual-comb laser, we achieve scan-less 3D imaging with nanometer precision and a 3D distance-imaging rate of 330 Hz, restricted only by the repetition rate difference of the dual-comb laser. Specifically, the FACED unit linearly arranges the laser beam into an array. A grating subsequently disperses this array transversely into lines, facilitating ultrafast spectroscopic applications that are 1–2 orders of magnitude quicker than traditional dual-comb methods. This spatiotemporal encoding also eases the stringent conditions on various dual-comb laser parameters, such as repetition rates, coherence, and stability. Through carefully designed experiments, we demonstrate that our scan-less system can measure 3D profiles of microfabricated structures at a rate of 7 million pixels per second. Our method significantly enhances measurement speed while maintaining high precision, using a compact light source. This advancement has the potential for broad applications, including phase imaging, surface topography, distance ranging, and spectroscopy.
Encoding information in the mutual coherence of spatially separated light beams
Nardi, Alfonso; Divitt, Shawn; Rossi, Massimiliano; et al. (2022)
Optics Letters
Coherence has been used as a resource for optical commu- nications since its earliest days. It is widely used for the multiplexing of data, but not for the encoding of data. Here we introduce a coding scheme, which we call mutual coher- ence coding, to encode information in the mutual coherence of spatially separated light beams. We describe its implemen- tation and analyze its performance by deriving the relevant figures of merit (signal-to-noise ratio, maximum bit-rate, and spectral efficiency) with respect to the number of trans- mitted beams. Mutual coherence coding yields a quadratic scaling of the number of transmitted signals with the num- ber of employed light beams, which might have benefits for cryptography and data security.
HfO$_2$-based platform for high-index-contrast visible and UV integrated photonics
Jaramillo, Oscar; Natarajan, Vighnesh; Rivy, Hamim Mahmud; et al. (2025)
Optics Letters
Ultraviolet and visible integrated photonics enable applications in quantum information, sensing, and spectroscopy, among others. Few materials support low-loss photonics into the UV, and the relatively low refractive index of known depositable materials limits the achievable functionality. Here, we present a high-index integrated photonics platform based on HfO$_2$ and Al$_2$O$_3$ composites deposited via atomic layer deposition (ALD) with low loss in the visible and near UV. We show that Al$_2$O$_3$ incorporation dramatically decreases bulk loss compared to pure HfO$_2$, consistent with inhibited crystallization due to the admixture of Al$_2$O$_3$. Composites exhibit refractive index n following the average of that of HfO$_2$ and Al$_2$O$_3$, weighted by the HfO$_2$ fractional composition x. At λ = 375 nm, composites with x = 0.67 exhibit n = 2.01, preserving most of HfO$_2$’s significantly higher index, and 3.8(7) dB/cm material loss. We further present fully etched and cladded waveguides, grating couplers, and ring resonators, realizing a single-mode waveguide loss of 0.25(2) dB/cm inferred from resonators of 2.6 million intrinsic quality factor at λ = 729 nm, 2.6(2) dB/cm at λ = 405 nm, and 7.7(6) dB/cm at λ = 375 nm. We measure the composite’s thermo-optic coefficient (TOC) to be 2.44(3) × 10$^{−5}$ RIU/°C near λ = 397 nm. This work establishes (HfO$_2$)$_x$(Al$_2$O$_3$)$_{1−x}$ composites as a platform amenable to integration for low-loss, high-index photonics spanning the UV to NIR.
Dispersion-engineered multi-pass cell for single-stage post-compression of an ytterbium laser
Silletti, Laura; Wahid, Ammar Bin; Escoto, Esmerando; et al. (2023)
Optics Letters
Post-compression methods for ultrafast laser pulses typically face challenging limitations, including saturation effects and temporal pulse breakup, when large compression factors and broad bandwidths are targeted. To overcome these lim-itations, we exploit direct dispersion control in a gas-filled multi-pass cell, enabling, for the first time to the best of our knowledge, single-stage post-compression of 150 fs pulses and up to 250 mu J pulse energy from an ytterbium (Yb) fiber laser down to sub-20 fs. Dispersion-engineered dielectric cav-ity mirrors are used to achieve nonlinear spectral broadening dominated by self-phase modulation over large compression factors and bandwidths at 98% throughput. Our method opens a route toward single-stage post-compression of Yb lasers into the few-cycle regime.Published by Optica Publishing Group under the terms of the Cre-ative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published arti-cle's title, journal citation, and DOI.
Swept dual-comb spectroscopy via common-mode cavity tuning and stabilization
Seidel, Moritz; Willenberg, Benjamin; Nussbaum-Lapping, Alexander; et al. (2025)
Optics Letters
We demonstrate common repetition rate sweeping in a single-cavity dual-comb laser for improving the resolution of spectroscopy measurements. As a proof of concept, we show spectroscopy of low-pressure acetylene, achieving an effective resolution of 50 MHz within an acquisition time of 0.8 s and a normalized signal-to-noise ratio (SNR) of 20 dBfHZ while using an Yb:CaF2 laser operating at a 1-GHz repetition rate. The high repetition rate of the laser enables phase tracking and access to a broad aliasing-free optical bandwidth exceeding 4 THz. During interleaving measurements, the spectroscopy comb is actively controlled while the second comb passively tracks the first. This ensures longterm stability of radio-frequency (RF) comb line positions and maintains a one-to-one correspondence between RF and optical comb line numbers following an initial calibration against a reference database. Spectral interleaving is realized by simultaneously sweeping the repetition rate of both combs via piezoelectric cavity length modulation. This system allows for dual-comb interleaving through control of a single degree of freedom, or frequency-stabilized interleaving with only two degrees of freedom. This provides an effective compromise between resolution, simplicity, and acquisition speed, thereby showcasing a new approach for the implementation of single-cavity dual-comb spectroscopy. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Polysilicon micro-heaters for resonance tuning in CMOS photonics
Krishna, Rakesh M.; Eftekhar, Ali; Lee, Sanghoon; et al. (2022)
Optics Letters
A new, to the best of our knowledge, device platform for tuning the resonance wavelength of integrated photonic resonators based on polysilicon-based micro-heaters for complementary metal-oxide semiconductor (CMOS)-foundry-based active Si photonics is demonstrated. The miniaturized micro-heater can be placed directly on the active Si layer, with a pedestal providing the optical and electrical isolation needed for the implementation of ultrafast active photonic devices such as modulators. The demonstrated devices do not require any additional modifications to the standard CMOS foundry processes. Experiments demonstrate a tuning efficiency of 0.25?nm/mW (or 42?GHz/mW) for a 5-µm-radius microdisk resonator with a loaded quality factor (Q) > 35,000. This polysilicon-based heater demonstrates a tunability of 42?GHz/mW with an average switching time of 60 µs. The proposed compact heater architecture enables it to be kept near to the optical mode, thereby providing efficient and high-speed wavelength tuning for resonant devices.
High-sensitivity pump-probe spectroscopy with a dual-comb laser and a PM-Andi supercontinuum
Gruber, Christoph; Pupeikis, Justinas; Camenzind, Sandro L.; et al. (2024)
Optics Letters
Amplifier-based pump-probe systems, while versatile, often suffer from complexity and low measurement speeds, especially when probing samples require low excitation fluences. To address these limitations, we introduce a pump-probe system that leverages a 60-MHz single-cavity dual-comb oscillator and an ultra-low noise supercontinuum. The setup can operate in equivalent time sampling or in programmable optical delay generation modes. We employ this system to study the wavelength-dependent excited-state dynamics of the non-fullerene electron acceptor Y6, a compound of interest in solar cell development, with excitation fluences as low as 1 nJ/cm2, well below the onset of nonlinear exciton annihilation effects. Our measurements reach a shot-noise limited sensitivity in differential transmission of 3.4·10–7. The results demonstrate the system’s potential to advance the field of ultrafast spectroscopy.

Publications 1 - 10 of 18

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