arXiv subjects

Martin E. Fermann

Publications and source records attributed to Martin E. Fermann.

15 recordsLinked to original sources

arXiv2025

Long-wave mid-infrared cavity-enhanced frequency comb spectroscopy of cold, complex molecules

We report the development of a new instrument for cavity-enhanced absorption spectroscopy of the fundamental rovibrational transitions of molecules in the long-wave mid-infrared (LWIR) region from 6500 to 10000 nm. Our setup combines a LWIR frequency comb, a high-finesse optical enhancement cavity, a cryogenic buffer gas cooling cell, and a Fourier transform interferometer to obtain broadband, high-resolution, and high-sensitivity molecular absorption spectra. Here, we showcase the capabilities of this setup by presenting the gas-phase LWIR spectra of the $\nu_6$ band of ethane and the $\nu_{10}$ band of the gauche conformer of ethanol near 7200 nm under both room temperature and cryogenic conditions.

physics.optics↗

arXiv2025

Fully stabilized Er fiber comb at 1 GHz by harmonic modelocking

Modelocked frequency comb lasers have always operated with a single pulse circulating in the laser cavity. This meant that each laser technology had an associated limit on pulse repetition rate. Achieving higher rates required different technology, for example exchanging optical fiber for solid state gain media. However, this is a perceived, rather than a fundamental limit. We demonstrate a new fiber laser design with multiple pulses circulating in the fiber gain cavity with the same high precision as a conventional fiber frequency comb. This has the immediate benefit of bringing mature fiber technology to higher repetition rate frequency combs. More generally, it adds great design freedom to laser engineering, where the laser can be separated into an optical cavity and a gain medium that are combined using standard frequency comb techniques. Fundamental frequency comb performance improvements may even be possible from the filtering intrinsic to our design, or by incorporating high stability cavities directly into the laser itself.

physics.optics↗

arXiv2022

Tunable VUV Frequency Comb for $^{\mathrm{229m}}$Th Nuclear Spectroscopy

Laser spectroscopy of the $^{\mathrm{229m}}$Th nuclear clock transition is necessary for the future construction of a nuclear-based optical clock. Precision laser sources with broad spectral coverage in the vacuum ultraviolet are needed for this task. Here, we present a tunable vacuum-ultraviolet frequency comb based on cavity-enhanced seventh-harmonic generation. Its tunable spectrum covers the current uncertainty range of the $^{\mathrm{229m}}$Th nuclear clock transition.

physics.optics↗

arXiv2021

Effects of a quiet point on a Kerr microresonator frequency comb

A quiet point, an operating point of pump-resonance detuning that minimizes frequency fluctuation due to nonlinear effects inside a resonator, has been employed for phase noise reduction of a soliton Kerr microresonator frequency comb (microcomb). Naturally, it is expected that the use of the point will also improve performances of a microcomb in terms of frequency stability and faithfulness in a phase locked loop. In this study, we experimentally investigate the effect in a microcomb with a repetition frequency of 300~GHz. We obtain a lowest fractional frequency instability at a quiet point of $1.5\times 10^{-9}$ at 1 second, which is 44 times lower than free-running instability. Phase-locking of a microcomb to a stabilized fiber comb is demonstrated to evaluate performance in a feedback loop, where in-loop-limited relative fractional frequency instability between the microcomb and the fiber comb of $6.8 \times 10^{-13}$ is obtained as an indicator of the stability limitation.

physics.optics↗

arXiv2020

300 GHz wave with attosecond-level timing noise

Optical frequency division (OFD) via optical frequency combs (OFC) has enabled a leap in microwave metrology leading to noise performance never explored before. Extending the method to millimeter-wave (mmW) and terahertz (THz)-wave domain is of great interest. Dissipative Kerr solitons (DKSs) in integrated photonic chips offer a unique feature of delivering OFCs with ultrahigh repetition rates from 10 GHz to 1 THz making them relevant gears to perform OFD in the mmW and THz-wave domain. We experimentally demonstrate OFD of an optically-carried 3.6 THz reference down to 300 GHz through a DKS, photodetected with an ultrafast uni-traveling-carrier photodiode (UTC-PD). A new measurement system, based on the characterization of a microwave reference phase-locked to the 300 GHz signal under test, yields attosecond-level timing noise sensitivity, leveraging conventional technical limitations. This work places DKSs as a leading technology in the mmW and THz-wave field promising breakthroughs in fundamental and civilian applications.

physics.optics↗

arXiv2019

Continuous scanning of a dissipative Kerr-microresonator soliton comb for broadband, high resolution spectroscopy

Dissipative Kerr-microresonator soliton combs (hereafter called soliton combs) are promising to realize chip scale integration of full soliton comb systems providing high precision, broad spectral coverage and a coherent link to the micro/mm/THz domain with diverse applications coming on line all the time. However, the large soliton comb spacing hampers some applications. For example, for spectroscopic applications, there are simply not enough comb lines available to sufficiently cover almost any relevant absorption features. Here, we overcome this limitation by scanning the comb mode spacing by employing PDH locking and a microheater on the microresonator, showing continuous scanning of the soliton comb modes across nearly the full FSR of the microresonator without losing soliton operation, while spectral features with a bandwidth of as small of 5 MHz are resolved. Thus, comb mode scanning allows to cover the whole comb mode spectrum of tens of THz bandwidth with only one chip-scale comb.

physics.app-ph↗

arXiv2018

Quantum state resolution of the C$_{60}$ fullerene

The remarkable physical properties of buckminsterfullerene, C$_{60}$, have attracted intense research activity since its original discovery. Total quantum state resolved measurements of isolated C$_{60}$ molecules have been of particularly long-standing interest. However, such observations have to date been unsuccessful due to the difficulty in preparing cold, gas-phase C$_{60}$ in sufficiently high densities. Here we report high resolution infrared absorption spectroscopy of C$_{60}$ in the 8.5 $μ$m spectral region. A combination of cryogenic buffer gas cooling and cavity-enhanced direct frequency comb spectroscopy has enabled the observation of quantum state resolved rovibrational transitions. Characteristic nuclear spin statistical intensity patterns provide striking confirmation of the indistinguishability of the sixty $^{12}$C atoms, while rovibrational fine structure encodes further details of the molecule's rare icosahedral symmetry. These observations establish new possibilities in the study and control of emergent complexity in finite-sized quantum systems such as fullerenes.

physics.chem-ph↗

arXiv2018

Phase-stabilized 100 mW frequency comb near 10 μm

Long-wavelength mid-infrared frequency combs with high power and flexible tunability are highly desired for molecular spectroscopy, including investigation of large molecules such as C60. We present a high power, phase-stabilized frequency comb near 10 μm, generated by a synchronously-pumped, singly-resonant optical parametric oscillator (OPO) based on AgGaSe2. The OPO can be continuously tuned from 8.4 to 9.5 μm, with a maximum average idler power of 100 mW at the center wavelength of 8.5 μm. Both the repetition rate (frep) and the carrier-envelop offset frequency (fceo) of the idler wave are phase-locked to microwave signals referenced to a Cs clock. We describe the detailed design and construction of the frequency comb, and discuss potential applications for precise and sensitive direct frequency comb spectroscopy.

physics.optics↗

arXiv2017

All-polarization-maintaining, single-port Er:fiber comb for high-stability comparison of optical lattice clocks

All-polarization-maintaining, single-port Er:fiber combs offer long-term robust operation as well as high stability. We have built two such combs and evaluated the transfer noise for linking optical clocks. A uniformly broadened spectrum over 135-285 THz with a high signal-to-noise ratio enables the optical frequency measurement of the subharmonics of strontium, ytterbium, and mercury optical lattice clocks with the fractional frequency-noise power spectral density of $(1-2)\times 10^{-17}$ Hz$^{-1/2}$ at 1 Hz. By applying a synchronous clock comparison, the comb enables clock ratio measurements with $10^{-17}$ instability at 1 s, which is one order of magnitude smaller than the best instability of the frequency ratio of optical lattice clocks.

physics.optics↗

arXiv2016

Optical frequency comb spectroscopy at 3-5.4 μm with a doubly resonant optical parametric oscillator

We present a versatile mid-infrared frequency comb spectroscopy system based on a doubly resonant optical parametric oscillator tunable in the 3-5.4 μm range and two detection methods, a Fourier transform spectrometer (FTS) and a Vernier spectrometer. Using the FTS with a multipass cell we measure high-precision broadband absorption spectra of CH$_4$ and NO at ~3.3 μm and ~5.2 μm, respectively, and of atmospheric species (CH$_4$, CO, CO$_2$ and H$_2$O) in air in the signal and idler wavelength range. The figure of merit of the system is on the order of 10$^{-8}$ cm$^{-1}$ Hz$^{-1/2}$ per spectral element, and multiline fitting yields minimum detectable concentrations of 10-20 ppb Hz$^{-1/2}$ for CH$_4$, NO and CO. For the first time in the mid-infrared, we perform continuous-filtering Vernier spectroscopy using a low finesse enhancement cavity, a grating and a single detector, and measure the absorption spectrum of CH$_4$ and H$_2$O in ambient air at ~3.3 μm.

physics.optics↗

arXiv2015

Surpassing the Path-Limited Resolution of a Fourier Transform Spectrometer with Frequency Combs

Fourier transform spectroscopy based on incoherent light sources is a well-established tool in research fields from molecular spectroscopy and atmospheric monitoring to material science and biophysics. It provides broadband molecular spectra and information about the molecular structure and composition of absorptive media. However, the spectral resolution is fundamentally limited by the maximum delay range (Δ$_{max}$) of the interferometer, so acquisition of high-resolution spectra implies long measurement times and large instrument size. We overcome this limit by combining the Fourier transform spectrometer with an optical frequency comb and measuring the intensities of individual comb lines by precisely matching the Δ$_{max}$ to the comb line spacing. This allows measurements of absorption lines narrower than the nominal (optical path-limited) resolution without ringing effects from the instrumental lineshape and reduces the acquisition time and interferometer length by orders of magnitude.

physics.optics↗

arXiv2012

Widely-tunable mid-IR frequency comb source based on difference frequency generation

We report on a mid-infrared frequency comb source of unprecedented tunability covering the entire 3-10 μm molecular fingerprint region. The system is based on difference frequency generation in a GaSe crystal pumped by a 151 MHz Yb:fiber frequency comb. The process was seeded with Raman shifted solitons generated in a highly nonlinear suspended-core fiber with the same source. Average powers up to 1.5 mW were achieved at 4.7 μm wavelength.

physics.optics↗

arXiv2011

Direct Frequency Comb Spectroscopy in the Extreme Ultraviolet

Development of the optical frequency comb has revolutionised metrology and precision spectroscopy due to its ability to provide a precise and direct link between microwave and optical frequencies. A novel application of frequency comb technology that leverages both the ultrashort duration of each laser pulse and the exquisite phase coherence of a train of pulses is the generation of frequency combs in the extreme ultraviolet (XUV) via high harmonic generation (HHG) in a femtosecond enhancement cavity. Until now, this method has lacked sufficient average power for applications, which has also hampered efforts to observe phase coherence of the high-repetition rate pulse train produced in the extremely nonlinear HHG process. Hence, the existence of a frequency comb in the XUV has not been confirmed. We have overcome both challenges. Here, we present generation of >200 μW per harmonic reaching 50 nm, and the observation of single-photon spectroscopy signals for both an argon transition at 82 nm and a neon transition at 63 nm. The absolute frequency of the argon transition has been determined via direct frequency comb spectroscopy. The resolved 10-MHz linewidth of the transition, limited by the transverse temperature of the argon atoms, is unprecedented in this spectral region and places a stringent upper limit on the linewidth of individual comb teeth. Due to the lack of cw lasers, these frequency combs are currently the only promising avenue towards extending ultrahigh precision spectroscopy to below the 100-nm spectral region with a wide range of applications that include spectroscopy of electronic transitions in molecules, experimental tests of bound state and many body quantum electrodynamics in He+ and He, development of next-generation "nuclear" clocks, and searches for spatial and temporal variation of fundamental constants using the enhanced sensitivity of highly charged ions.

physics.atom-ph↗

arXiv2011

Ultra-Broadband Coherent Supercontinuum Frequency Comb

We present detailed studies of the coherence properties of an ultra-broadband super-continuum, enabled by a new approach involving continuous wave laser sources to independently probe both the amplitude and phase noise quadratures across the entire spectrum. The continuum coherently spans more than 1.5 octaves, supporting Hz-level comparison of ultrastable lasers at 698 nm and 1.54 μm. We present the first numerical simulation of the accumulated comb coherence in the limit of many pulses, in contrast to the single-pulse level, with systematic experimental verification. The experiment and numerical simulations reveal the presence of quantum-seeded broadband amplitude noise without phase coherence degradation, including the discovery of a dependence of the super-continuum coherence on the fiber fractional Raman gain.

physics.optics↗

arXiv2009

Phase-stabilized, 1.5-W frequency comb at 2.8 to 4.8 micron

We present a high-power optical parametric oscillator-based frequency comb in the mid-infrared wavelength region using periodically poled lithium niobate. The system is synchronously pumped by a 10-W femtosecond Yb:fiber laser centered at 1.07 um and is singly resonant for the signal. The idler (signal) wavelength can be continuously tuned from 2.8 to 4.8 um (1.76 to 1.37 um) with a simultaneous bandwidth as high as 0.3 um and a maximum average idler output power of 1.50 W. We also demonstrate the performance of the stabilized comb by recording the heterodyne beat with a narrow-linewidth diode laser. This OPO is an ideal source for frequency comb spectroscopy in the mid-IR.

physics.optics↗