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1.
Opt Express ; 32(1): 26-39, 2024 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-38175053

RESUMO

Dual-comb lasers are a new class of ultrafast lasers that enable fast, accurate and sensitive measurements without any mechanical delay lines. Here, we demonstrate a 2-µm laser called MIXSEL (Modelocked Integrated eXternal-cavity Surface Emitting Laser), based on an optically pumped passively modelocked semiconductor thin disk laser. Using III-V semiconductor molecular beam epitaxy, we achieve a center wavelength in the shortwave infrared (SWIR) range by integrating InGaSb quantum well gain and saturable absorber layers onto a highly reflective mirror. The cavity setup consists of a linear straight configuration with the semiconductor MIXSEL chip at one end and an output coupler a few centimeters away, resulting in an optical comb spacing between 1 and 10 GHz. This gigahertz pulse repetition rate is ideal for ambient pressure gas spectroscopy and dual-comb measurements without requiring additional stabilization. In single-comb operation, we generate 1.5-ps pulses with an average output power of 28 mW, a pulse repetition rate of 4 GHz at a center wavelength of 2.035 µm. For dual-comb operation, we spatially multiplex the cavity using an inverted bisprism operated in transmission, achieving an adjustable pulse repetition rate difference estimated up to 4.4 MHz. The resulting heterodyne beat reveals a low-noise down-converted microwave frequency comb, facilitating coherent averaging.

2.
Opt Express ; 32(9): 15093-15105, 2024 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-38859168

RESUMO

We report on a femtosecond thulium laser operating on the 3H4 → 3H5 transition with upconversion pumping around 1 µm and passively mode-locked by a GaSb-based SEmiconductor Saturable Absorber Mirror (SESAM). This laser employs a 6 at.% Tm:LiYF4 laser crystal and a polarization maintaining Yb-fiber master oscillator power amplifier at 1043 nm as a pump source addressing the 3F4 → 3F2,3 excited-state absorption transition of Tm3+ ions. In the continuous-wave regime, the Tm-laser generates 616 mW at ∼2313 nm with a slope efficiency of 10.0% (vs. the incident pump power) and a linear polarization (π). By implementing a type-I SESAM with a single ternary strained In0.33Ga0.67Sb quantum well embedded in GaSb for sustaining and stabilizing the soliton pulse shaping, the self-starting mode-locked Tm-laser generated pulses as short as 870 fs at a central wavelength of 2309.4 nm corresponding to an average output power of 208 mW at a pulse repetition rate of 105.08 MHz and excellent mode-locking stability. The output power was scaled to 450 mW at the expense of a longer pulse duration of 1.93 ps. The nonlinear parameters of the SESAM are also reported.

3.
Opt Lett ; 49(7): 1766-1769, 2024 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-38560858

RESUMO

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.

5.
Appl Opt ; 63(15): 4144-4156, 2024 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-38856508

RESUMO

We investigate terahertz time-domain spectroscopy using a low-noise dual-frequency-comb laser based on a single spatially multiplexed laser cavity. The laser cavity includes a reflective biprism, which enables generation of a pair of modelocked output pulse trains with slightly different repetition rates and highly correlated noise characteristics. These two pulse trains are used to generate the THz waves and detect them by equivalent time sampling. The laser is based on Yb:CALGO, operates at a nominal repetition rate of 1.18 GHz, and produces 110 mW per comb with 77 fs pulses around 1057 nm. We perform THz measurements with Fe-doped photoconductive antennas, operating these devices with gigahertz 1 µm lasers for the first time, to our knowledge, and obtain THz signal currents approximately as strong as those from reference measurements at 1.55 µm and 80 MHz. We investigate the influence of the laser's timing noise properties on THz measurements, showing that the laser's timing jitter is quantitatively explained by power-dependent shifts in center wavelength. We demonstrate reduction in noise by simple stabilization of the pump power and show up to 20 dB suppression in noise by the combination of shared pumping and shared cavity architecture. The laser's ultra-low-noise properties enable averaging of the THz waveform for repetition rate differences from 1 kHz to 22 kHz, resulting in a dynamic range of 55 dB when operating at 1 kHz and averaging for 2 s. We show that the obtained dynamic range is competitive and can be well explained by accounting for the measured optical delay range, integration time, as well as the measurement bandwidth dependence of the noise from transimpedance amplification. These results will help enable a new approach to high-resolution THz-TDS enabled by low-noise gigahertz dual-comb lasers.

6.
Opt Express ; 31(21): 34313-34324, 2023 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-37859191

RESUMO

We present a SESAM modelocked Yb:YAG solid-state laser providing low-noise narrowband pulses with a pulse duration of 606 fs at a 1.09-GHz repetition rate, delivering up to 2.5 W of average output power. This laser provides access to a new parameter space that could previously not be reached by solid-state lasers and, to the best of our knowledge, is the first modelocked solid-state Yb:YAG laser in the gigahertz regime. This is achieved by introducing a single additional intracavity element, specifically a nonlinear birefringent YVO4 crystal, for soliton formation, polarization selection, and cavity intensity clamping. The isotropic pump absorption in Yb:YAG allows for stable and low-noise operation with multimode fiber pumping. This laser is ideally suited as a seed source for many commercial high-power Yb-doped amplification systems operating at a center wavelength around 1.03 µm. The laser exhibits a high power per comb line of 5.0 mW which also makes it interesting for applications in frequency comb spectroscopy, especially if it is used to pump an optical parametric oscillator. We measure a relative intensity noise (RIN) of 0.03%, integrated from 1 Hz to 10 MHz. Furthermore, we show that the laser timing jitter for noise frequencies >2 kHz is fully explained by a power-dependent shift in the center wavelength of 0.38 nm/W due to the quasi-three-level laser gain material. The narrow gain bandwidth of Yb:YAG reduces this contribution to noise in comparison to other SESAM modelocked Yb-doped lasers.

7.
Opt Express ; 31(4): 6475-6483, 2023 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-36823902

RESUMO

We present the first dual-modelocked femtosecond oscillator operating beyond 2 µm wavelength. This new class of laser is based on a Cr:ZnS gain medium, an InGaSb SESAM for modelocking, and a two-surface reflective device for spatial duplexing of the two modelocked pulse trains (combs). The laser operates at 2.36 µm, and for each comb, we have achieved a FWHM spectral bandwidth of 30 nm, an average power of over 200 mW, and a pulse duration close to 200 fs. The nominal repetition rate is 242 MHz with a sufficiently large repetition rate difference of 4.17 kHz. We also found that the laser is able to produce stable modelocked pulses over a wide range of output powers. This result represents a significant step towards realizing dual-comb applications directly above 2 µm using a single free-running laser.

8.
Opt Express ; 31(4): 6633-6648, 2023 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-36823915

RESUMO

Single-cavity dual-combs comprise a rapidly emerging technology platform suitable for a wide range of applications like optical ranging, equivalent time sampling, and spectroscopy. However, it remains a challenging task to develop a dual-comb system that exhibits low relative frequency fluctuations to allow for comb line resolved measurements, while simultaneously offering high average power and short pulse durations. Here we combine a passively cooled and compact dual-comb solid-state oscillator with a pair of core-pumped Yb-fiber-based amplifiers in a master-oscillator power-amplifier (MOPA) architecture. The Yb:KYW oscillator operates at 250 MHz and uses polarization multiplexing for dual-comb generation. To the best of our knowledge, this is the first demonstration of a single-cavity dual-comb based on this gain material. As the pulse timing characteristics inherent to the oscillator are preserved in the amplification process, the proposed hybrid approach leverages the benefit of both the ultra-low noise solid-state laser and the advantages inherent to fiber amplifier systems such as straight-forward power scaling. The amplifier is optimized for minimal pulse broadening while still providing significant amplification and spectral broadening. We obtain around 1 W of power per output beam with pulses then compressed down to sub-90 fs using a simple grating compressor, while no pre-chirping or other dispersion management is needed. The full-width half-maximum (FWHM) of the radio-frequency comb teeth is 700 Hz for a measurement duration of 100 ms, which is much less than the typical repetition rate difference, making this passively stable source well-suited for indefinite coherent signal averaging via computational phase tracking.

9.
Opt Express ; 30(22): 39691-39705, 2022 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-36298915

RESUMO

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.

10.
Opt Express ; 30(4): 5019-5025, 2022 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-35209473

RESUMO

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.

11.
Opt Express ; 30(15): 27662-27673, 2022 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-36236932

RESUMO

Ultrafast laser systems operating with high-average power in the wavelength range from 1.9 µm to 3 µm are of interest for a wide range of applications for example in spectroscopy, material processing and as drivers for secondary sources in the XUV spectral region. In this area, laser systems based on holmium-doped gain materials directly emitting at 2.1 µm have made significant progress over the past years, however so far only very few results were demonstrated in power-scalable high-power laser geometries. In particular, the thin-disk geometry is promising for directly modelocked oscillators with high average power levels that are comparable to amplifier systems at MHz repetition rate. In this paper, we demonstrate semiconductor saturable absorber mirror (SESAM) modelocked Ho:YAG thin-disk lasers (TDLs) emitting at 2.1-µm wavelength with record-holding performance levels. In our highest average power configuration, we reach 50 W of average power, with 1.13-ps pulses, 2.11 µJ of pulse energy and ∼1.9 MW of peak power. To the best of our knowledge, this represents the highest average power, as well as the highest output pulse energy so far demonstrated from a modelocked laser in the 2-µm wavelength region. This record performance level was enabled by the recent development of high-power GaSb-based SESAMs with low loss, adapted for high intracavity power and pulse energy. We also explore the limitations in terms of reaching shorter pulse durations at high power with this gain material in the disk geometry and using SESAM modelocking, and present first steps in this direction, with the demonstration of 30 W of output power, with 692-fs pulses in another laser configuration. In the near future, with the development of a next generation of SESAM samples for this wavelength region, we believe higher pulse energy approaching the 10-µJ regime, and sub-500-fs pulses should be straightforward to reach using SESAM modelocking.

12.
Opt Express ; 30(21): 37245-37260, 2022 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-36258316

RESUMO

Long-distance ranging is a crucial tool for both industrial and scientific applications. Laser-based distance metrology offers unprecedented precision making it the ideal approach for many deployments. In particular, dual-comb ranging is favorable due to its inherently high precision and sampling rate. To make high-performance long-range dual-comb LiDAR more accessible by reducing both cost and complexity, here we demonstrate a fiber-based dual-comb LiDAR frontend combined with a free-running diode-pumped solid-state dual-comb laser that allows for sub-µm measurement precision while offering a theoretical ambiguity range of more than 200 km. Our system simultaneously measures distance with the role of each comb interchanged, thereby enabling Vernier-based determination of the number of ambiguity ranges. As a proof-of-principle experiment, we measure the distance to a moving target over more than 10 m with sub-µm precision and high update rate, corresponding to a relative precision of 10-7. For a static target at a similar distance, we achieve an instantaneous precision of 0.29 µm with an update time of 1.50 ms. With a longer averaging time of 200 ms, we reach a precision of around 33 nm, which corresponds to a relative precision of about 3·10-9 with a time-of-flight-based approach.

13.
Hum Reprod ; 37(4): 822-827, 2022 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-35139195

RESUMO

STUDY QUESTION: How did the coronavirus disease 2019 (COVID-19) pandemic affect live birth numbers in Europe? SUMMARY ANSWER: In 14 European countries with validated datasets on live birth numbers during the ongoing COVID-19 pandemic, excess mortality was inversely correlated with live birth numbers. WHAT IS KNOWN ALREADY: Since March 2020, in order to minimize spread of severe acute respiratory syndrome coronavirus 2 and reducing strain on the health care systems, many national authorities have imposed containments and restricted both indoor and outdoor recreational activities. Historical events, such as electricity blackouts, have repeatedly been shown to exert incremental effects on birth numbers. STUDY DESIGN, SIZE, DURATION: We evaluated the effect of the COVID-19 pandemic and the containments on reproduction and birth numbers in 14 European countries with complete and validated datasets, until March 2021. PARTICIPANTS/MATERIALS, SETTING, METHODS: The national demographic offices of 20 European countries were requested to provide the monthly birth numbers from 2015 to March 2021. Among them, 14 countries provided those data. Taking into account seasonal variations, the live birth numbers were compared with excess mortality at two different time intervals during the pandemic. MAIN RESULTS AND THE ROLE OF CHANCE: At 9 months after the initiation of containments in many European countries, 11 of 14 European countries (78.5%) experienced a decline in live birth numbers, ranging between -0.5% and -11.4%. The decline in live birth numbers was most pronounced in eight European countries with the highest degree of excess mortality. From January to March 2021, live birth numbers continued to decline in 5 of 8 European countries with high excess mortality, whereas live births started to recover in 8 of 14 countries (57.1%). LIMITATIONS, REASONS FOR CAUTION: The live birth numbers of some key European countries were not available. WIDER IMPLICATIONS OF THE FINDINGS: The demographic changes linked to the COVID-19 pandemic may add to the overall socio-economic consequences, most particularly in those countries with pre-existing reduced reproduction rates. STUDY FUNDING/COMPETING INTEREST(S): This study did not receive specific funding. The authors have no conflicts of interest to declare. TRIAL REGISTRATION NUMBER: N/A.


Assuntos
COVID-19 , Coeficiente de Natalidade , Europa (Continente)/epidemiologia , Feminino , Fertilização in vitro , Humanos , Nascido Vivo/epidemiologia , Pandemias , Gravidez
14.
Phys Rev Lett ; 128(6): 063001, 2022 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-35213184

RESUMO

Capturing electronic dynamics in real time has been the ultimate goal of attosecond science since its beginning. While for atomic targets the existing measurement techniques have been thoroughly validated, in molecules there are open questions due to the inevitable copresence of moving nuclei, which are not always mere spectators of the phototriggered electron dynamics. Previous work has shown that not only can nuclear motion affect the way electrons move in a molecule, but it can also lead to contradictory interpretations depending on the chosen experimental approach. In this Letter we investigate how nuclear motion affects and eventually distorts the electronic dynamics measured by using two of the most popular attosecond techniques, reconstruction of attosecond beating by interference of two-photon transitions and attosecond streaking. Both methods are employed, in combination with ab initio theoretical calculations, to retrieve photoionization delays in the dissociative ionization of H_{2}, H_{2}→H^{+}+H+e^{-}, in the region of the Q_{1} series of autoionizing states, where nuclear motion plays a prominent role. We find that the experimental reconstruction of attosecond beating by interference of two-photon transitions results are very sensitive to bond softening around the Q_{1} threshold (27.8 eV), even at relatively low infrared (IR) intensity (I_{0}∼1.4×10^{11} W/cm^{2}), due to the long duration of the probe pulse that is inherent to this technique. Streaking, on the other hand, seems to be a better choice to isolate attosecond electron dynamics, since shorter pulses can be used, thus reducing the role of bond softening. This conclusion is supported by very good agreement between our streaking measurements and the results of accurate theoretical calculations. Additionally, the streaking technique offers the necessary energy resolution to accurately retrieve the fast-oscillating phase of the photoionization matrix elements, an essential requirement for extending this technique to even more complicated molecular targets.

15.
Appl Phys B ; 128(2): 24, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35125672

RESUMO

Semiconductor saturable absorber mirrors (SESAMs) have enabled a wide variety of modelocked laser systems, which makes measuring their nonlinear properties an important step in laser design. Here, we demonstrate complete characterization of SESAMs using an equivalent time sampling apparatus. The light source is a free-running dual-comb laser, which produces a pair of sub-150-fs modelocked laser outputs at 1051 nm from a single cavity. The average pulse repetition rate is 80.1 MHz, and the full time window is scanned at 240 Hz. Cross-correlation between the beams is used to calibrate the time axis of the measurements, and we use a non-collinear pump-probe geometry on the sample. The measurements enable fast and robust determination of all the nonlinear reflectivity and recovery time parameters of the devices from a single setup, and show good agreement with conventional nonlinear reflectivity measurements. We compare measurements to a rate equation model, showing good agreement up to high pulse fluence values and revealing that the samples tested exhibit a slightly slower recovery at higher fluence values. Lastly, we examine the polarization dependence of the reflectivity, revealing a reduced rollover if cross-polarized beams are used or if the sample is oriented optimally around the beam axis.

16.
Int Urogynecol J ; 33(6): 1601-1608, 2022 06.
Artigo em Inglês | MEDLINE | ID: mdl-35129645

RESUMO

INTRODUCTION AND HYPOTHESIS: Postpartum urinary retention (PUR) may cause long-term urogenital tract morbidity. The incidence ranges from 0.18 to 14.6%, but the importance of prompt diagnosis and appropriate management is often underappreciated. The paucity of data on long-term outcome after PUR contributes to these drawbacks. The aim of this study was to assess long-term persistence of elevated PVR (post-void residual urine) volume after PUR. Pathophysiology, risk factors and management of PUR are reviewed. METHODS: In our tertiary referral urogynecology unit in the University Women's Hospital of Bern, Switzerland, all patients who were referred for PUR were asked to participate in this study. PVR was measured sonographically every 2 days until day 15, then after 6, 12, 24 and 36 months and, if increased, the patients were instructed to perform clean intermittent self-catheterization. If retention persisted longer than the lactation period, multichannel urodynamics was performed. RESULTS: Sixty-two patients were included. The median PVR normalized at day 7. Long-term voiding disorders were found in 8.2%, 6.7%, and 4.9% after 1, 2, and 3 years respectively. Multichannel urodynamics confirmed in all patients with persisting retention an acontractile detrusor and de novo stress urinary incontinence in 4 cases. Quantile regression did not reveal any factor contributing to earlier recovery. Eighty-nine percent of the patients with PUR had operative vaginal deliveries, emphasizing the importance of this risk factor for PUR. CONCLUSIONS: In most cases PUR resolves early, but voiding difficulties persist more often than previously thought, and for these patients the consequences are devastating. Obstetric awareness, early active management, and developing management strategies in the postpartum period might preclude lower urinary tract morbidity.


Assuntos
Cateterismo Uretral Intermitente , Transtornos Puerperais , Retenção Urinária , Parto Obstétrico/efeitos adversos , Feminino , Humanos , Cateterismo Uretral Intermitente/efeitos adversos , Período Pós-Parto , Gravidez , Transtornos Puerperais/epidemiologia , Transtornos Puerperais/etiologia , Retenção Urinária/epidemiologia , Retenção Urinária/etiologia , Retenção Urinária/terapia
17.
Opt Express ; 29(16): 24910-24918, 2021 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-34614835

RESUMO

Laser ranging (LIDAR) with dual optical frequency combs enables high-resolution distance measurements over long ranges with fast update rates. However, the high complexity of stabilized dual optical frequency comb systems makes it challenging to use this technique in industrial applications. To address this issue, here we demonstrate laser ranging directly from the output of both a free-running dual-comb diode-pumped semiconductor and solid-state laser oscillator. Dual-comb operation from a single cavity is achieved via polarization duplexing with intracavity birefringent crystals. We perform ranging experiments with two implementations of this scheme: a modelocked integrated external cavity surface-emitting laser (MIXSEL) and a Yb:CaF2 solid-state laser. For these proof of principle demonstrations, we measure the distance to a moving mirror mounted on a home-made shaker. The MIXSEL laser has a repetition rate of 2.736 GHz and a repetition rate difference of 52 kHz, and yields a measurement resolution of 1.36 µm. The Yb:CaF2 laser has a repetition rate of 137 MHz and a repetition rate difference of 952 Hz, and yields a measurement resolution of 0.55 µm. In both cases the resolution is inferred by a parallel measurement with a HeNe interferometer. These results represent the first laser ranging with free-running dual-comb solid-state oscillators. With further optimization, resolution well below 1 µm and range well above 1 km are expected with this technique.

18.
Opt Express ; 29(24): 40360-40373, 2021 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-34809379

RESUMO

We compare the gain and continuous wave lasing properties of two InGaSb-based vertical external cavity surface emitting lasers (InGaSb VECSEL) with different heat management approaches operating at a center wavelength of around 2µ m. To date, intracavity heatspreaders have been required for good average output power, which have many trade-offs, especially for passive modelocking. Here we demonstrate a record high average output power of 810 mW without an intracavity heatspreader using a backside-cooled non-resonant VECSEL chip optimized for modelocking. In addition, we introduce and demonstrate an optical characterization for a wavelength range of 1.9 to 3µ m to precisely measure wavelength-dependent gain saturation and spectral gain. Gain characteristics are measured as a function of wavelength, fluence, pump power and temperature. Small signal gain of more than 5%, small saturation fluences and broad gain bandwidths of more than 90 nm are demonstrated. In comparison to a commercial VECSEL chip with an intracavity heatspreader, we have obtained similar average output power even though our VECSEL chip is designed for antiresonance.

19.
Opt Express ; 29(5): 6647-6656, 2021 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-33726181

RESUMO

Semiconductor saturable absorber mirrors (SESAMs) are widely used for modelocking of various ultrafast lasers. The growing interest for SESAM-modelocked lasers in the short-wave infrared and mid-infrared regime requires precise characterization of SESAM parameters. Here, we present two SESAM characterization setups for a wavelength range of 1.9 to 3 µm to precisely measure both nonlinear reflectivity and time-resolved recovery dynamics. For the nonlinear reflectivity measurement, a high accuracy (<0.04%) over a wide fluence range (0.1-1500 µJ/cm2) is achieved. Time-resolved pump-probe measurements have a resolution of about 100 fs and a scan range of up to 680 ps. Using the two setups, we have fully characterized three different GaSb-SESAMs at an operation wavelength of 2.05 µm fabricated in the FIRST lab at ETH Zurich. The results show excellent performance suitable for modelocking diode-pumped solid-state and semiconductor disk lasers. We have measured saturation fluences of around 4 µJ/cm2, modulation depths varying from 1% to 2.4%, low non-saturable losses (∼ 0.2%) and sufficiently fast recovery times (< 32 ps). The predicted influence of Auger recombination in the GaSb material system is also investigated.

20.
Opt Express ; 29(4): 5774-5781, 2021 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-33726109

RESUMO

Quantum cascade detectors (QCD) are photovoltaic mid-infrared detectors based on intersubband transitions. Owing to the sub-picosecond carrier transport between subbands and the absence of a bias voltage, QCDs are ideally suited for high-speed and room temperature operation. Here, we demonstrate the design, fabrication, and characterization of 4.3 µm wavelength QCDs optimized for large electrical bandwidth. The detector signal is extracted via a tapered coplanar waveguide (CPW), which was impedance-matched to 50 Ω. Using femtosecond pulses generated by a mid-infrared optical parametric oscillator (OPO), we show that the impulse response of the fully packaged QCDs has a full-width at half-maximum of only 13.4 ps corresponding to a 3-dB bandwidth of more than 20 GHz. Considerable detection capability beyond the 3-dB bandwidth is reported up to at least 50 GHz, which allows us to measure more than 600 harmonics of the OPO repetition frequency reaching 38 dB signal-to-noise ratio without the need of electronic amplification.

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