arXiv subjects

Maciej Kowalczyk

Publications and source records attributed to Maciej Kowalczyk.

9 recordsLinked to original sources

arXiv2026

Shot-noise-limited few-cycle mid-infrared frequency comb with attosecond phase stability

Achieving sub-cycle waveform control with attosecond-level precision while reaching shot-noise-limited amplitude stability in the mid-infrared spectral range remains a central challenge for ultrafast and precision optical science. Here, we demonstrate a fully stabilized, ultra-stable optical frequency comb (OFC) based on a Kerr-lens mode-locked Cr:ZnS laser operating at 2.3 $μ$m. The oscillator delivers 40 fs pulses at a 25 MHz repetition rate, which are spectrally broadened to cover two octaves and compressed to a 1.4-cycle, 11 fs duration. Pumped by a custom low-noise erbium-doped fiber amplifier, the laser exhibits an integrated relative intensity noise (RIN) of 0.0026% over 10 Hz--1 MHz, while the noise of the few-cycle output is further suppressed to 0.0017% and reaches the shot-noise limit for Fourier frequencies above 5 kHz. It represents the lowest amplitude noise reported to date for any mode-locked laser. This unprecedented amplitude stability enables carrier-envelope phase (CEP) stabilization with a residual integrated phase noise of only 1.5 mrad (10 Hz--12.5 MHz), corresponding to a CEP jitter of 1.8 as, the highest phase stability for any laser system ever reported. The long-term performance of the fully stabilized OFC is measured over 24 hours, with a power stability of 0.01% and a residual CEP noise of 17 mrad. By combining few-cycle mid-infrared pulses with shot-noise-limited intensity noise and attosecond-level phase stability, the reported OFC provides access to new regimes of quantum-limited metrology and control of ultrafast light-matter interactions.

physics.optics↗

arXiv2026

GHz-bandwidth InAs/InAsSbP barrier infrared detectors for the 3.0-3.7 μm spectral region operating at room temperature

The demand for fast mid-wave infrared photodetectors is fueled by high-rate free-space optical communication and optical frequency comb spectroscopy. To date, only a few multi-GHz photodetectors have shown sensitive room-temperature operation in the 3.0-3.7 μm band, yet their commercial availability remains scarce. In this work, we present the remarkable response speed of an InAs/InAsSbP nBp barrier detector - a type typically not associated with high-frequency operation. A weakly reverse-biased photodiode with a diameter of 121 μm achieves a -3 dB electrical bandwidth of 2.4 GHz and -20 dB bandwidth of 8.0 GHz. This is the best result in this class of mid-infrared photodetectors confirmed optically. High signal-to-noise photodetection is also demonstrated at frequencies exceeding 19 GHz. The relatively simple device structure (devoid of cascaded structure or type-II superlattice) was realized on the mature InAs material platform, which opens new perspectives for accessible, sensitive, multi-GHz photodetectors for the 3.0-3.7 μm spectral region.

physics.optics↗

arXiv2025

Revisiting semiclassical effective dynamics for quantum cosmology

We revise the technique of semiclassical effective dynamics, in particular reexamining the evaluation of Poisson structure of the so-called central moments capturing quantum corrections, providing a systematic, pedagogical, and efficient algorithm for evaluation of said structure. The resulting closed formulae for Poisson brackets involve less summatios than recent results in the literature, thus being more optimal for applications. Found formulae are then applied to a general class of isotropic cosmological models with locally observable configuration variables for the admitted matter fields. In particular, this allowed to formulate a consistent and nontrivial limit or fiducial cell (infrared regulator) removal for models describing spatially noncompact spacetimes.

gr-qc↗

arXiv2025

Primodial power spectrum in loop quantum cosmology for different regularizations

In Loop Quantum Cosmology, the quantization of the Hamiltonian constraint involves a regularization procedure which is affected by certain ambiguities. Moreover, different regularizations lead to distinct mathematical formulations and, consequently, to different physical predictions. In this work, we explore the impact of this regularization on the primordial power spectrum of cosmological perturbations. More specifically, we study this power spectrum for the conventional regularization used in Loop Quantum Cosmology and for two alternative prescriptions suggested in the literature. We set initial conditions for the perturbations at the bounce corresponding to a recently proposed vacuum state, optimally adapted to the background dynamics. This choice of vacuum is based on an asymptotic Hamiltonian diagonalization in the ultraviolet sector of the perturbations which provides a non-oscillating power spectrum. Employing a suitable approximation to the propagation equations of the perturbations around the bounce, we are able to obtain an analytic expression for the primordial power spectrum of this vacuum for all the discussed regularizations. We compare the results and prove that the main relevant distinction between the corresponding spectra is the scale where power suppression occurs. The associated wavenumber scale is proportional to the square root of the critical density in Loop Quantum Cosmology, density which is different for each of the studied regularizations.

gr-qc↗

arXiv2024

Choice of vacuum state and the relation between inflationary and Planck scales

Recent observations about the cosmic microwave background evidence a clear discrepancy between the scale of inflation and the Planck scale expected in the conventional inflationary picture, based on simple chaotic inflationary models. This paper explores a possible resolution of this conflict by considering a slight modification of the standard general relativity scenario, which naturally incorporates a cutoff scale consistent with the observations. This last scale of power suppression appears by the combined effect of the preinflationary background dynamics and an associated initial vacuum state for the cosmological perturbations which differs from the conventional Bunch-Davies state of slow-roll inflation. We revise and correct previous discussions in the literature about the relation between this scale and the scale corresponding to the onset of inflation. The mechanism that produces this cutoff is intimately related to the criterion determining a privileged vacuum state for the primordial perturbations. We adhere to a recent proposal based on an asymptotic diagonalization of the Hamiltonian of the perturbations and leading to a non-oscillatory primordial power spectrum. With this choice, we are able to investigate analytically the model, studying in detail some physically interesting cases. These analytic calculations provide further support to our arguments about the relation between the different scales of the system.

gr-qc↗

arXiv2024

Dual-dispersion-regime dual-comb mode-locked laser

We report on the first solid-state dual-comb mode-locked laser simultaneously operating in different dispersion regimes. Due to the intrinsic polarization-multiplexing in a birefringent Yb:Ca$_3$NbGa$_3$Si$_2$O$_{14}$ (Yb:CNGS) gain medium, the laser emits two cross-polarized pulse trains with a repetition rate offset of ~4.8 kHz from a single cavity. We obtain dual pulse generation with 20-fold difference in the duration, by setting the net cavity group delay dispersion to cross zero across the emission band of the employed gain medium. While the duration of the soliton-like pulses experiencing anomalous dispersion amounts to 117 fs, the second laser output that is spectrally located in the normal dispersion region, is strongly chirped with a pulse duration of 2360 fs.

physics.optics↗

arXiv2022

Regularizations and quantum dynamics in loop quantum cosmology

One of critical components of Loop Quantum Gravity (LQG) and Cosmology (LQC) -- Thiemann regularization procedure is non-unique. Different choices of particular prescriptions lead to models which differ in both mathematical structure and physical predictions. Here we briefly recall a set of such prescriptions proposed in the literature in context of isotropic LQC on the example of a flat universe with massless scalar matter content. For the one least investigated so far, further called Yang-Ding-Ma prescription, a detailed analysis of its mathematical structure and resulting quantum dynamics is performed, confirming and extending the results obtained so far by phenomenological methods. In order to probe the dynamics, a relatively robust method (working in the approximation of the macroscopic universe) of evaluating quantum trajectories is devised. Said method is a variant of a semiclassical treatment that allows to express the trajectories analytically as function of internal clock and a set of certain central moments -- constants of motion encoding quantum corrections up to arbitrary order in systematic manner. As a test of method's robustness analogous evaluation of the quantum trajectory in volume is performed for those of other prescriptions, for which it is applicable. The limitations of the treatment are further briefly discussed.

gr-qc↗

arXiv2021

Consequences of regularization ambiguities in Loop Quantum Cosmology

Ambiguities of the so-called Thiemann regularization in Loop Quantum Cosmology lead to freedom in how to construct a particular quantization prescription. So far three distinct examples of such have been proposed in the literature. For two of them, detailed analysis has been already performed in the literature. In this thesis, the methodology developed for these is applied to study in detail the third one, which will be referred to as mLQC-II. In particular, the mathematical properties of the operator of the quantum version of full Hamiltonian constraint are examined. These properties indicate that the evolution of the system is uniquely determined. Furthermore, an investigation of dynamics is performed by finding the expectation value of the volume as a function of the scalar field and constants of motion. This result is next compared to the trajectories predicted with the so-called effective dynamics. Finally, the main properties of studied prescription are compared against those of other (already investigated) ones.

gr-qc↗

arXiv2020

Dual-comb femtosecond solid-state laser with inherent polarization-multiplexing

Dual-comb spectroscopy is a rapidly developing technique enabling ultraprecise broadband optical diagnostics of atoms and molecules. This powerful tool typically requires two phase-locked femtosecond lasers, yet it has been shown that it can be realized without any stabilization if the combs are generated from a single laser cavity. Still, unavoidable intrinsic relative phase-fluctuations always set a limit on the precision of any spectroscopic measurements, hitherto limiting the applicability of bulk dual-comb lasers for mode-resolved studies. Here, we demonstrate a versatile concept for low-noise dual-comb generation from a single-cavity femtosecond solid-state laser based on intrinsic polarization-multiplexing inside an optically anisotropic gain crystal. Due to intracavity spatial separation of the orthogonally-polarized beams, two sub-100 fs pulse trains are simultaneously generated from a 1.05 $μ$m Yb:CNGS oscillator with a repetition rate difference of 4.7 kHz. The laser exhibits the lowest relative noise ever demonstrated for a bulk dual-comb source, supporting free-running mode-resolved spectroscopic measurements over a second. Moreover, the developed dual-comb generation technique can be applied to any solid-state laser exploiting a birefringent active crystal, paving the way towards a new class of highly-coherent, single-cavity, dual-comb laser sources operating in various spectral regions.

physics.optics↗