Optics Express

Journal: Optics Express

Abbreviation

Opt. Express

Publisher

Optica

ISSN

1094-4087

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Publications 1 - 10 of 66

Influence of disk aberrations on high-power thin-disk laser cavities
Seidel, Moritz; Lang, Lukas; Phillips, Christopher R.; et al. (2022)
Optics Express
We present a systematic study on the influence of thin-disk aberrations on the performance of thin-disk laser oscillators. To evaluate these effects, we have developed a spatially resolved numerical model supporting arbitrary phase profiles on the intracavity components that estimates the intracavity beam shape and the output power of thin-disk laser oscillators. By combining this model with the experimentally determined phase profile of the thin-disk (measured with interferometry), we can predict the operation mode of high-power thin-disk lasers, including mode degradation, higher-order mode coupling, and stability zone shrinking, all of which are in good agreement with experiment. Our results show that one of the main mechanisms limiting the performance is the small deviation of the disk’s phase profile from perfect radial symmetry. This result is an important step to scaling modelocked thin-disk oscillators to the kW-level and will be important in the design of future active multi-pass cavity arrangements.
Composition-controlled recovery time of SWIR (2–2.4 µm) GaSb-based SESAMs
Schuchter, Maximilian C.; Gaulke, Marco; Huwyler, Nicolas; et al. (2025)
Optics Express
SEmiconductor Saturable Absorber Mirrors (SESAMs) have revolutionized the ultrafast laser industry. While SESAMs are well-established in the near-infrared regime, using GaAs-wafer epitaxy, there is an increasing interest for the short-wave infrared (SWIR) regime, for which SESAMs can be fabricated using the GaSb material system. Compared to GaAs-based SESAMs, the nonlinear response of GaSb absorbers has been reported to exhibit inherent ultrafast response and a different interplay between the response time and fabrication process. Here we report new advanced features of this interplay in a detailed study investigating the effects of lattice mismatch (LMM, e.g., strain) in the quantum wells (QWs), and barrier materials of SESAMs designed for a center wavelength between 2 and 2.4 µm. At 2 µm, SESAMs with ternary InGaSb, GaAsSb, and quaternary In(x)Ga(1-x)As(y)Sb(1-y) QWs embedded in GaSb were grown with varying levels of QW LMM, ranging from compressive strain (-1.7% LMM) to tensile strain (+0.9% LMM). We observed a strong dependence of the recovery time on the QW strain. While a maximum interband recovery time of 340 ps was measured for lattice matched QWs (-0.1% LMM), both compressively and tensilely strained QWs exhibit a shorter interband recovery time. Furthermore, a set of In0.27GaSb QW SESAMs embedded in AlxGa1−xAsSb barriers with different Al content have been grown. We observed that an increasing Al content in the barrier significantly slows down the interband recovery time. All findings are consistent for different heterostructures designed for operation at 2–2.4 µm.
Detailed analysis of the interference patterns measured in lab-based X-ray dual-phase grating interferometry through wave propagation simulation
Tang, Ruizhi; Organista, Caori; Goethals, Wannes; et al. (2023)
Optics Express
In this work, we analyze the interference patterns measured in lab-based dual-phase grating interferometry and for the first time explain the spatial dependencies of the measured interference patterns and the large visibility deviations between the theoretical prediction and the experimental results. To achieve this, a simulator based on wave propagation is developed. This work proves that the experimental results can be simulated with high accuracy by including the effective grating thickness profile induced by the cone-beam geometry, the measured detector response function and a non-ideal grating shape. With the comprehensive understanding of dual-phase grating interferometry, this provides the foundations for a more efficient and accurate algorithm to retrieve sample’s structure information, and the realistic simulator is a useful tool for optimizing the set-up.
Supercontinuum-based hyperspectral LiDAR for precision laser scanning
Ray, Pabitro; Salido Monzú, David; Camenzind, Sandro L.; et al. (2023)
Optics Express
Hyperspectral LiDAR enables non-contact mapping of the 3D surface geometry of an object along with its spectral reflectance signature and has proved to be effective for automated point cloud segmentation in various remote sensing applications. The established hyperspectral LiDAR methods offer a range precision of a few mm to a few cm for distances exceeding several meters. We propose a novel approach to hyperspectral LiDAR scanning based on a supercontinuum (SC) coherently broadened from a 780 nm frequency comb. It provides high precision distance measurements along with target reflectance over the 570–970 nm range of the SC output. The distance measurements are carried out by monitoring the differential phase delay of intermode beat notes generated by direct photodetection, while the backscattered light spectrum is acquired using a commercial CCD spectrometer with 0.16 nm resolution across the 400 nm bandwidth of the SC output. We demonstrate a measurement precision below 0.1 mm for a stand-off range up to 50 m on a diffuse target with around 89% reflectance. The measured relative accuracy as compared to a reference interferometer is on the order of 10−5 for distances up to 50 m. Initial results also indicate spectrum-based material classification within a 3D point cloud using a linear support vector machine. The results highlight the potential of this approach for joint high-precision laser scanning and automated material classification.
Quantum cascade laser absorption spectrometer with a low temperature multipass cell for precision clumped CO2 measurement
Nataraj, Akshay; Gianella, Michele; Prokhorov, Ivan; et al. (2022)
Optics Express
We present a quantum cascade laser-based absorption spectrometer deploying a compact (145 mL volume) segmented circular multipass cell (SC-MPC) with 6 m optical path length. This SC-MPC is embedded into an effective cooling system to facilitate operation at cryogenic temperatures. For CO₂, the sample is cooled to 153 K, i.e. close to the sublimation point at 10 mbar. This enables efficient suppression of interfering hot-band transitions of the more abundant isotopic species and thereby enhances analytical precision. As a demonstration, the amount fractions of all three CO₂ isotopologues involved in the kinetic isotope exchange reaction of ¹²C¹⁶O₂ + ¹²C¹⁸O₂ ⇌ 2·¹²C¹⁶O¹⁸O are measured. The precision in the ratios [¹²C¹⁸O₂]/[¹²C¹⁶O₂] and [¹²C¹⁶O¹⁸O]/[¹²C¹⁶O₂] is 0.05 ‰ with 25 s integration time. In addition, we determine the variation of the equilibrium constant, K, of the above exchange reaction for carbon-dioxide samples equilibrated at 300 K and 1273 K, respectively.
Dual-comb optical parametric oscillator in the mid-infrared based on a single free-running cavity
Bauer, Carolin P.; Camenzind, Sandro L.; Pupeikis, Justinas; et al. (2022)
Optics Express
We demonstrate a free-running single-cavity dual-comb optical parametric oscillator (OPO) pumped by a single-cavity dual-comb solid-state laser. The OPO ring cavity contains a single periodically-poled MgO-doped LiNbO3 (PPLN) crystal. Each idler beam has more than 245-mW average power at 3550 nm and 3579 nm center wavelengths (bandwidth 130 nm). The signal beams are simultaneously outcoupled with more than 220 mW per beam at 1499 nm and 1496 nm center wavelength. The nominal repetition rate is 80 MHz, while the repetition rate difference is tunable and set to 34 Hz. To evaluate the feasibility of using this type of source for dual-comb applications, we characterize the noise and coherence properties of the OPO signal beams. We find ultra-low relative intensity noise (RIN) below -158 dBc/Hz at offset frequencies above 1 MHz. A heterodyne beat note measurement with a continuous wave (cw) laser is performed to determine the linewidth of a radio-frequency (RF) comb line. We find a full-width half-maximum (FWHM) linewidth of around 400 Hz. Moreover, the interferometric measurement between the two signal beams reveals a surprising property: the center of the corresponding RF spectrum is always near zero frequency, even when tuning the pump repetition rate difference or the OPO cavity length. We explain this effect theoretically and discuss its implications for generating stable low-noise idler combs suitable for high-sensitivity mid-infrared dual-comb spectroscopy (DCS).
Refractivity corrected distance measurement using the intermode beats derived from a supercontinuum
Ray, Pabitro; Salido Monzú, David; Presl, Robert; et al. (2024)
Optics Express
Simultaneous distance measurements on two or more optical wavelengths enable dispersion-based correction of deviations that result from insufficient knowledge of the refractive index along the signal propagation path. We demonstrate a supercontinuum-based approach for highly accurate distance measurements suitable for such an inline refractivity compensation. The distance is estimated from the phase delay observations on the intermode beats. We use a supercontinuum (SC) coherently broadened from a 780 nm frequency comb and spanning the spectral range of 570-970 nm. Experiments are performed on the 590 and 890 nm wavelength bands filtered from the SC spectrum. Results show distance measurements with standard deviations of around 0.01 mm at 50 m, and a distance-dependent component below 0.2 ppm on the individual spectral bands. Distance residuals compared to a reference interferometer are on the order of 0.1 ppm for displacements up to 50 m. Controlled pressure-induced refractivity variations are created over a length of 15 m, resulting in an optical path length change of 0.4 mm. Using the two-color method, we demonstrate refractivity-corrected distance measurement with a standard deviation of around 0.08 mm for a 60 s averaging window. The current experimental configuration can be easily extended to distance measurements on more than two wavelengths. The results highlight its potential for practical long-distance measurements through inline refractivity compensation.
Glass-in-glass infiltration for 3D micro-optical composite components
Casamenti, Enrico; Torun, Gözden; Borasi, Luciano; et al. (2022)
Optics Express
Chalcogenide glass exhibits a wide transmission window in the infrared range, a high refractive index, and nonlinear optical properties; however, due to its poor mechanical properties and low chemical and environmental stability, producing three-dimensional microstructures of chalcogenide glass remains a challenge. Here, we combine the fabrication of arbitrarily shaped three-dimensional cavities within fused silica molds by means of femtosecond laser-assisted chemical etching with the pressure-assisted infiltration of a chalcogenide glass into the resulting carved silica mold structures. This process enables the fabrication of 3D, geometrically complex, chalcogenide-silica micro-glass composites. The resulting products feature a high refractive index contrast that enables total-internal-reflection guiding and an optical quality roughness level suited for applications in the infrared.
High-power low-noise 2-GHz femtosecond laser oscillator at 2.4 µm
Barh, Ajanta; Alaydin, Özgür; Heidrich, Jonas; et al. (2022)
Optics Express
Femtosecond lasers with high repetition rates are attractive for spectroscopic applications with high sampling rates, high power per comb line, and resolvable lines. However, at long wavelengths beyond 2 µm, current laser sources are either limited to low output power or repetition rates below 1 GHz. Here we present an ultrafast laser oscillator operating with high output power at multi-GHz repetition rate. The laser produces transform-limited 155-fs pulses at a repetition rate of 2 GHz, and an average power of 0.8 W, reaching up to 0.7 mW per comb line at the center wavelength of 2.38 µm. We have achieved this milestone via a Cr2+-doped ZnS solid-state laser modelocked with an InGaSb/GaSb SESAM. The laser is stable over several hours of operation. The integrated relative intensity noise is 0.15% rms for [10 Hz, 100 MHz], and the laser becomes shot noise limited (-160 dBc/Hz) at frequencies above 10 MHz. Our timing jitter measurements reveal contributions from pump laser noise and relaxation oscillations, with a timing jitter of 100 fs integrated over [3 kHz, 100 MHz]. These results open up a path towards fast and sensitive spectroscopy directly above 2 µm.
Strain-engineered vertical emitting InGaAsSb quantum well lasers at 2–2.4 µm: in-well vs. barrier pumping, silicate bonding, and thermal optimization
Schuchter, Maximilian C.; Huwyler, Nicolas; Golling, Matthias; et al. (2025)
Optics Express
We present a comprehensive study of continuous-wave (cw) lasing in GaSb-based membrane external cavity surface emitting lasers (MECSELs) operating in the 2.0–2.4 µm range. Using both in-well and barrier pumping, we investigate the influence of quantum well (QW) strain in eight InGaAsSb-based MECSEL structures. A key advance is the implementation of silicate bonding, which improves fabrication yield from <10% (for direct bonding) to >60% by relaxing surface flatness requirements of GaSb wafers. In addition, we show that only compressively strained QWs with lattice mismatch >1% lase. This is supported by theoretical calculations showing that the imbalance between the density of states (DOS) in the conduction and valence bands limits the ability to reach population inversion, even though sufficient TE-polarized gain is available in all structures. At 2 µm, in-well and barrier pumping provide similar slope efficiencies (∼29% over absorbed power), but in-well pumping achieves a record-low thermal resistance of 0.5 ± 0.1 K/W by eliminating pump-absorbing barrier layers. At 2.35 µm, slope efficiency drops (∼6.8% for in-well, ∼10.7% for barrier pumping), likely due to increased Auger recombination at longer wavelength. The in-well design maintains superior thermal performance (0.6 ± 0.2 K/W thermal resistance). These results position in-well pumped MECSELs as a thermally efficient, wavelength-scalable platform for short-wave infrared (SWIR) applications including gas sensing, medical diagnostics, and molecular spectroscopy.

Publications 1 - 10 of 66

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