arXiv subjects

Christopher R. Phillips

Publications and source records attributed to Christopher R. Phillips.

10 recordsLinked to original sources

arXiv2025

3D in-situ profiling in a laser micromachining station using dual-comb LiDAR

One of the main challenges in laser micromachining is the complexity of the process development. The available monitoring capabilities are mostly limited to external measurement systems, significantly slowing down this step. We address this limitation by integrating a coaxial dual-comb LiDAR system directly into a laser micromachining station, enabling in-situ, non-destructive 3D profiling without removing the workpiece. The sub-micron raw axial precision of the system, the operation without mechanical delay scanning and a large working range make the system well-suited for profiling a large variety of micromachined structures. By providing in-situ feedback this approach will significantly accelerate laser micromachining process development.

physics.optics↗

arXiv2024

Long-range and dead-zone free dual-comb ranging for the interferometric tracking of moving targets

Dual-comb ranging has emerged as an effective technology for long-distance metrology, providing absolute distance measurements with high speed, precision, and accuracy. Here, we demonstrate a dual-comb ranging method that utilizes a free-space transceiver unit, enabling dead-zone-free measurements and simultaneous ranging with interchanged comb roles to allow for long-distance measurements even when the target is moving. It includes a GPU-accelerated algorithm for real-time signal processing and a free-running single-cavity solid-state dual-comb laser with a carrier wavelength $\lambda_c \approx$ 1055 nm, a pulse repetition rate of 1 GHz and a repetition rate difference of 5.06 kHz. This combination offers a fast update rate and sufficient signal strength to reach a single-shot time-of-flight precision of around 0.1 $\mu$m (i.e. $< \lambda_c/4$) on a cooperative target placed at a distance of more than 40 m. The free-running laser is sufficiently stable to use the phase information for interferometric distance measurements, which improves the single-shot precision to $<$20 nm. To assess the ranging accuracy, we track the motion of the cooperative target when moved over 40 m and compare it to a reference interferometer. The residuals between the two measurements are below 3 $\mu$m. These results highlight the potential of this approach for accurate and dead-zone-free long-distance ranging, supporting real-time tracking with nm-level precision.

physics.optics↗

arXiv2024

High-sensitivity dual-comb and cross-comb spectroscopy across the infrared using a widely-tunable and free-running optical parametric oscillator

Coherent dual-comb spectroscopy (DCS) enables high-resolution measurements at high speeds without the trade-off between resolution and update rate inherent to mechanical delay scanning approaches. However, high system complexity and limited measurement sensitivity remain major challenges for DCS. Here, we address these challenges via a wavelength-tunable dual-comb optical parametric oscillator (OPO) combined with an up-conversion detection method. The OPO is tunable in the short-wave infrared (1300-1670 nm range) and mid-infrared (2700- 5000 nm range) where many molecules have strong absorption bands. Both OPO pump beams are generated in a single spatially-multiplexed laser cavity, while both signal and idler beams are generated in a single spatially-multiplexed OPO cavity. The near-common path of the combs in this new configuration enables comb-line-resolved and aliasing-free measurements in free-running operation. By limiting the instantaneous idler bandwidth to below 1 THz, we obtain a high power per comb line in the mid-infrared of up to 160 $μ$W. With a novel intra-cavity nonlinear up-conversion scheme based on cross-comb spectroscopy, we leverage these power levels while overcoming the sensitivity limitations of direct mid-infrared detection, leading to a high signal-to-noise ratio (50.2 dB Hz$^{1/2}$) and record-level dual-comb figure of merit (3.5\times 10^8 Hz$^{1/2}$). As a proof of concept, we demonstrate the detection of methane with 2-ppm concentration over 3-m path length. Our results demonstrate a new paradigm for DCS compatible with high-sensitivity and high-resolution measurements over a wide spectral range.

physics.optics↗

arXiv2023

Gigahertz Single-cavity Dual-comb Laser for Rapid Time-domain Spectroscopy: from Few Terahertz to Optical Frequencies

Dual-comb generation from a single laser cavity provides a simple and high-performance solution to time sampling applications. We demonstrate a compact single-cavity dual-comb laser operating at gigahertz repetition rates and high repetition rate differences up to more than 100 kHz with sub-100 fs pulse duration. The single cavity approach leads to passive common noise suppression resulting in ultra-low relative timing jitter and fully resolvable comb lines in free-running operation. We showcase the laser performance with two application demonstrations: (a) time-domain spectroscopy of acetylene in the near-infrared via computational comb line tracking and (b) free-space THz time domain spectroscopy and thickness-measurements via adaptive sampling. For (b) we use efficient state-of the art iron-doped InGaAs photoconductive antennas to generate and detect the THz light. Here we operate these devices with an efficient Yb-based gigahertz repetition rate laser for the first time. One optical comb generates the THz light, while the other probes it via equivalent time sampling. We obtain signal strengths comparable to reference measurements with MHz repetition rate Er-based laser systems while achieving close to 1 GHz spectral resolution (defined by the comb line spacing) and generating THz frequencies up to 3 THz. By carrying out a careful investigation of the noise properties of the laser we confirm that the free-running gigahertz dual-comb oscillator provides a rapid yet highly precise optical delay sweep from a simple setup. Therefore, our approach will be beneficial for high-update rate time sampling and time-domain spectroscopy applications.

physics.optics↗

arXiv2022

Timing jitter characterization of free-running dual-comb laser with sub-attosecond resolution using optical heterodyne detection

Pulse trains emitted from dual-comb systems are designed to have low relative timing jitter, making them useful for many optical measurement techniques such as optical ranging and spectroscopy. However, the characterization of low-jitter dual-comb systems is challenging because it requires measurement techniques with high sensitivity. Motivated by this challenge, we developed a technique based on an optical heterodyne detection approach for measuring the relative timing jitter of two pulse trains. The method is suitable for dual-comb systems with essentially any repetition rate difference. Furthermore, the proposed approach allows for continuous and precise tracking of the sampling rate. To demonstrate the technique, we perform a detailed characterization of a single-mode-diode pumped $\mathrm{Yb:CaF_2}$ dual-comb laser from a free-running polarization-multiplexed cavity. This new laser produces 115 fs pulses at 160 MHz repetition rate, with 130 mW of average power in each comb. The detection noise floor for the relative timing jitter between the two pulse trains reaches $8.0 \times 10^{-7} \, \mathrm{fs}^2/\mathrm{Hz} \; ( \sim 896 \: \mathrm{zs}/\sqrt{\mathrm{Hz}} )$, and the relative root mean square (rms) timing jitter is 13 fs when integrating from 100 Hz to 1 MHz. This performance indicates that the demonstrated laser is highly compatible with practical dual-comb spectroscopy, ranging, and sampling applications. Furthermore, our results show that the relative timing noise measurement technique can characterize dual-comb systems operating in free-running mode or with finite repetition rate differences while providing a sub-attosecond resolution, which was not feasible with any other approach before.

physics.ins-det↗

arXiv2021

Picosecond ultrasonics with a free-running dual-comb laser

We present a free-running 80-MHz dual-comb polarization-multiplexed solid-state laser which delivers 1.8 W of average power with 110-fs pulse duration per comb. With a high-sensitivity pump-probe setup, we apply this free-running dual-comb laser to picosecond ultrasonic measurements. The ultrasonic signatures in a semiconductor multi-quantum-well structure originating from the quantum wells and superlattice regions are revealed and discussed. We further demonstrate ultrasonic measurements on a thin-film metalized sample and compare these measurements to ones obtained with a pair of locked femtosecond lasers. Our data show that a free-running dual-comb laser is well-suited for picosecond ultrasonic measurements and thus it offers a significant reduction in complexity and cost for this widely adopted non-destructive testing technique.

physics.optics↗

arXiv2020

High-power few-cycle near-infrared OPCPA for soft X-ray generation at 100 kHz

We present a near-infrared optical parametric chirped-pulse amplifier (OPCPA) and soft X-ray (SXR) high-harmonic generation system. The OPCPA produces few-cycle pulses at a center wavelength of 800 nm and operates at a high repetition rate of 100 kHz. It is seeded by fully programmable amplitude and phase controlled ultra-broadband pulses from a Ti:sapphire oscillator. The output from the OPCPA system was compressed to near-transform-limited 9.3-fs pulses. High-power operation up to an average power of 35 W was achieved, and a fully characterized pulse compression was recorded for a power level of 22.5 W, demonstrating pulses with a peak power greater than 21 GW. We demonstrate that at such high repetition rates, spatiotemporally flattened pump pulses can be achieved through a cascaded second-harmonic generation approach with an efficiency of more than 70%, providing a compelling OPCPA architecture for power-scaling ultra-broadband systems in the near-infrared. The output of this 800-nm OPCPA system was used to generate SXR radiation reaching 190 eV photon energy through high-harmonic generation in helium.

physics.optics↗

arXiv2019

Water window soft x-ray source enabled by 25-W few-cycle mid-IR OPCPA at 100 kHz

Coherent soft x-ray (SXR) sources enable fundamental studies in the important water window spectral region. Until now, such sources have been limited to repetition rates of 1 kHz or less, which limits count rates and signal-to-noise ratio for a variety of experiments. SXR generation at high repetition rate has remained challenging because of the missing high-power mid-infrared (mid-IR) laser sources to drive the high-harmonic generation (HHG) process. Here we present a mid-IR optical parametric chirped pulse amplifier (OPCPA) centered at a wavelength of 2.2 μm and generating 16.5-fs pulses (2.2 oscillation cycles of the carrier wave) with 25 W of average power and a peak power exceeding 14 GW at 100-kHz pulse repetition rate. This corresponds to the highest reported peak power for high-repetition-rate mid-IR laser systems. The output of this 2.2-μm OPCPA system was used to generate a SXR continuum extending beyond 0.6 keV through HHG in a high-pressure gas cell.

physics.optics↗

arXiv2019

Ultrabroadband Nonlinear Optics in Nanophotonic Periodically Poled Lithium Niobate Waveguides

Quasi-phasematched interactions in waveguides with quadratic nonlinearities enable highly efficient nonlinear frequency conversion. In this article, we demonstrate the first generation of devices that combine the dispersion-engineering available in nanophotonic waveguides with quasi-phasematched nonlinear interactions available in periodically poled lithium niobate (PPLN). This combination enables quasi-static interactions of femtosecond pulses, reducing the pulse energy requirements by several orders of magnitude, from picojoules to femtojoules. We experimentally demonstrate two effects associated with second harmonic generation. First, we observe efficient quasi-phasematched second harmonic generation with <100 fJ of pulse energy. Second, in the limit of strong phase-mismatch, we observe spectral broadening of both harmonics with as little as 2-pJ of pulse energy. These results lay a foundation for a new class of nonlinear devices, in which co-engineering of dispersion with quasi-phasematching enables efficient nonlinear optics at the femtojoule level.

physics.optics↗

arXiv2014

Mid-infrared pulse generation via achromatic quasi-phase-matched OPCPA

We demonstrate a new regime for mid-infrared optical parametric chirped pulse amplification (OPCPA) based on achromatic quasi-phase-matching. Our mid-infrared OPCPA system is based on collinear aperiodically poled lithium niobate (APPLN) pre-amplifiers and a non-collinear PPLN power amplifier. The idler output has a bandwidth of 800 nm centered at 3.4 $μ$m. After compression, we obtain a pulse duration of 44.2 fs and a pulse energy of 21.8 $μ$J at a repetition rate of 50 kHz. We explain the wide applicability of the non-collinear QPM amplification scheme we used, including how it can enable octave-spanning OPCPA in a single device when combined with an aperiodic QPM grating.

physics.optics↗