Compact Yb fiber few-cycle pulse source based on precision pulse compression and shaping with an adaptive fiber Bragg grating.

We generate bandwidth limited 10 µJ pulses of 92 fs pulse width using an adaptive fiber Bragg grating stretcher (FBG) in conjunction with a Lyot filter. The temperature controlled FBG is used to optimize the group delay, whereas the Lyot filter counteracts gain narrowing in the amplifier chain. Soliton compression in a hollow core fiber (HCF) allows for access to the few-cycle pulse regime. Adaptive control further enables the generation of nontrivial pulse shapes.

Coherent frequency transfer with < 5*10-21 stability via a multi-branch comb with noise cancellation.

We demonstrate a multi-branch frequency comb for spectral purity transfer incorporating hardware enabled noise cancellation based on a cw noise transfer laser. We verify coherent frequency transfer at stabilities ≈ 2×10-18 in 1 second and < 5×10-21 in 10,000 seconds without any reference cavity.

Coherent supercontinuum shaping for multiple wavelength optimization over an octave.

We shape the spectrum of an octave spanning supercontinuum from an erbium fiber laser. The group delay dispersion is controlled through the temperature profile of a chirped fiber Bragg grating. We demonstrate control of spectral broadening, switching in spectral windows, and optimizing power at six wavelengths corresponding to Yb, Ca, and Sr clock transitions, an f-2f pair, and a C-band reference for frequency transfer applications. We verify locking of the shaped f-2f beat note, and the coherence of the shaped supercontinuum by interference with an unshaped supercontinuum branch with relative frequency deviation of 10-17 at 1 s averaging time.

Tunable VUV frequency comb for 229mTh nuclear spectroscopy.

Laser spectroscopy of the 229mTh 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 229mTh nuclear clock transition.

Direct Comb Vernier Spectroscopy for Fractional Isotopic Ratio Determinations.

Accurate isotopic composition analysis of the greenhouse-gasses emitted in the atmosphere is an important step to mitigate global climate warnings. Optical frequency comb-based spectroscopic techniques have shown ideal performance to accomplish the simultaneous monitoring of the different isotope substituted species of such gases. The capabilities of one such technique, namely, direct comb Vernier spectroscopy, to determine the fractional isotopic ratio composition are discussed. This technique combines interferometric filtering of the comb source in a Fabry-Perot that contains the sample gas, with a high resolution dispersion spectrometer to resolve the spectral content of each interacting frequency inside of the Fabry-Perot. Following this methodology, simultaneous spectra of ro-vibrational transitions of 12C16O2 and 13C16O2 molecules are recorded and analyzed with an accurate fitting procedure. Fractional isotopic ratio 13C/12C at 3% of precision is measured for a sample of CO2 gas, showing the potentialities of the technique for all isotopic-related applications of this important pollutant.

Low noise, self-referenced all polarization maintaining Ytterbium fiber laser frequency comb: erratum.

We provide a corrected figure of our previous publication [Opt. Express25, 18017 (2017)10.1364/OE.25.018017].

Author Correction: Absolute spectroscopy near 7.8 µm with a comb-locked extended-cavity quantum-cascade-laser.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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 Pound-Drever-Hall locking and a microheater on the microresonator, showing continuous scanning of the soliton comb modes across nearly the full free-spectral range of the microresonator without losing soliton operation, while spectral features with a bandwidth as small as 5 MHz are resolved.

Control of Kerr-microresonator optical frequency comb by a dual-parallel Mach-Zehnder interferometer.

A technique to integrate key functions of a Kerr-microresonator optical frequency comb into one device, i.e., a dual-parallel Mach-Zehnder interferometer (DP-MZI), is proposed. In the technique, a DP-MZI enables the control of carrier envelope offset frequency (fceo), as well as repetition frequency (frep), in addition to generating a stable dissipative Kerr soliton. In experiments, influences on fceo and frep by pump frequency and power modulation via a DP-MZI are investigated, followed by a demonstration of long-term full stabilization of a microresonator soliton comb to a fiber-based optical frequency comb. As another example demonstration, timing jitter of a microresonator soliton comb is significantly suppressed by referencing to a fiber through a two-wavelength delayed self-heterodyne interferometer (TWDI).

Rovibrational quantum state resolution of the C60 fullerene.

The unique physical properties of buckminsterfullerene, C60, have attracted intense research activity since its original discovery. Total quantum state-resolved spectroscopy of isolated C60 molecules has been of particularly long-standing interest. Such observations have, to date, been unsuccessful owing to the difficulty in preparing cold, gas-phase C60 in sufficiently high densities. Here we report high-resolution infrared absorption spectroscopy of C60 in the 8.5-micron spectral region (1180 to 1190 wave number). 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 confirm the indistinguishability of the 60 carbon-12 atoms, while rovibrational fine structure encodes further details of the molecule's rare icosahedral symmetry.

Low-noise millimeter-wave synthesis from a dual-wavelength fiber Brillouin cavity.

In this Letter, a photonic system is proposed to generate millimeter waves with low phase noise and ultra-high frequency stability. By locking two free-running CW lasers to the same fiber cavity whose free-spectral range is actively stabilized, millimeter waves can be synthesized in a wide frequency range with fine-tuning capability. Exploiting the spectral narrowing effect of stimulated Brillouin scattering, the generated millimeter waves exhibit low phase noise that does not scale up as the frequency increases. In the experimental demonstration, up to ∼300 GHz millimeter waves are generated, with a phase noise of <-90 dBc/Hz at 10 kHz offset limited by the local oscillator and an in-loop 60 min frequency RMS drift of 0.43 mHz. The output frequency of the system can be readily increased to sub-THz region by replacing one of the pump CW lasers.

Photonics-enabled wideband microwave burst detection.

In this Letter, to the best of our knowledge, a novel wideband microwave burst detection system is realized by utilizing photonics-assisted wavelength and time division multiplexing, in conjunction with optical storage. Deploying a coherent electro-optical dual comb and a recirculating optical frequency shifter with ∼1.28 µs round-rip delay, the proof-of-concept experimental system demonstrates the interrogation of ∼1 µs radio frequency (RF) bursts with up to an 8 GHz bandwidth and arbitrary hopping pattern at 1 MHz resolution and a refresh rate of ∼60 kHz using an 80 MHz RF detection unit. The proposed system can be easily upgraded to higher bandwidths and longer burst time apertures with suitable hardware.

Absolute spectroscopy near 7.8 µm with a comb-locked extended-cavity quantum-cascade-laser.

We report for the first time the frequency locking of an extended-cavity quantum-cascade-laser (EC-QCL) to a near-infrared frequency comb. The locked laser source is exploited to carry out molecular spectroscopy around 7.8 µm with a line-centre frequency combined uncertainty of ~63 kHz. The strength of the approach, in view of an accurate retrieval of line centre frequencies over a spectral range as large as 100 cm-1, is demonstrated on the P(40), P(18) and R(31) lines of the fundamental rovibrational band of N2O covering the centre and edges of the P and R branches. The spectrometer has the potential to be straightforwardly extended to other spectral ranges, till 12 µm, which is the current wavelength limit for commercial cw EC-QCLs.

Phase-stabilized 100 mW frequency comb near 10 µm.

Long-wavelength mid-infrared (MIR) 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 (f rep) and the carrier-envelope offset frequency (f ceo) 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.

Fast ultra-wideband microwave spectral scanning utilizing photonic wavelength- and time-division multiplexing.

A high-speed ultra-wideband microwave spectral scanning system is proposed and experimentally demonstrated. Utilizing coherent dual electro-optical frequency combs and a recirculating optical frequency shifter, the proposed system realizes wavelength- and time-division multiplexing at the same time, offering flexibility between scan speed and size, weight and power requirements (SWaP). High-speed spectral scanning spanning from ~1 to 8 GHz with ~1.2 MHz spectral resolution is achieved experimentally within 14 µs. The system can be easily scaled to higher bandwidth coverage, faster scanning speed or finer spectral resolution with suitable hardware.

Low noise, self-referenced all polarization maintaining Ytterbium fiber laser frequency comb.

We report the implementation of a self-referenced optical frequency comb generated by a passively mode-locked all polarization maintaining (PM) Yb fiber laser based on a nonlinear amplifying loop mirror (NALM). After spectral broadening the optical spectrum spans from 650 nm to 1400 nm, allowing for the generation of an optical octave and carrier envelope offset frequency (fceo) stabilization through a conventional f-2f interferometer. We demonstrate for the first time the stabilization of the fceo of such a PM Yb system with an in-loop fractional frequency stability scaled to an optical frequency of low 10-19 at 1 second averaging time, offering a great potential for applications in optical atomic clock metrology.

Three-photon absorption in optical parametric oscillators based on OP-GaAs.

We report on, to the best of our knowledge, the first singly resonant (SR), synchronously pumped optical parametric oscillator (OPO) based on orientation-patterned gallium arsenide (OP-GaAs). Together with a doubly resonant (DR) degenerate OPO based on the same OP-GaAs material, the output spectra cover 3 to 6 µm within ∼3 dB of relative power. The DR-OPO has the highest output power reported to date from a femtosecond, synchronously pumped OPO based on OP-GaAs. We observed strong three-photon absorption with a coefficient of 0.35±0.08 cm3/GW2 for our OP-GaAs sample, which limits the output power of these OPOs as mid-IR light sources. We present a detailed study of the three-photon loss on the performance of both the SR- and DR-OPOs, and compare them to those without this loss mechanism.

Low noise electro-optic comb generation by fully stabilizing to a mode-locked fiber comb.

A fully stabilized EO comb is demonstrated by phase locking the two degrees of freedom of an EO comb to a low noise mode-locked fiber comb. Division/magnification of residual phase noise of locked beats is observed by measuring an out-of-loop beat. By phase locking the 200 th harmonics of the EO comb and a driving cw frequency to a fiber comb, a record low phase noise EO comb across +/- 200 harmonics (from 1544.8 nm to 1577.3 nm) is demonstrated.

Fourier transform and Vernier spectroscopy using an optical frequency comb at 3-5.4 µm.

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 continuous-filtering Vernier spectrometer (CF-VS). Using the FTS with a multipass cell, we measure high precision broadband absorption spectra of CH4 at 3.3 µm and NO at 5.25 µm, the latter for the first time with comb spectroscopy, and we detect atmospheric species (CH4, CO, CO2, and H2O) in air in the signal and idler ranges. Multiline fitting yields minimum detectable concentrations of 10-20 ppb Hz-1/2 for CH4, NO, and CO. For the first time in the mid-infrared, we perform CF-VS using an enhancement cavity, a grating, and a single detector, and we measure the absorption spectrum of CH4 and H2O in ambient air at ∼3.3 µm, reaching a 40 ppb concentration detection limit for CH4 in 2 ms.

Self-referenced, accurate and sensitive optical frequency comb spectroscopy with a virtually imaged phased array spectrometer.

We present a cavity-enhanced direct optical frequency comb spectroscopy system with a virtually imaged phased array (VIPA) spectrometer and either a dither or a Pound-Drever-Hall (PDH) locking scheme used for stable transmission of the comb through the cavity. A self-referenced scheme for frequency axis calibration is shown along with an analysis of its accuracy. A careful comparison between both locking schemes is performed based on near-IR measurements of the carbon monoxide ν=3←0 band P branch transitions in a gas sample with known composition. The noise-equivalent absorptions (NEA) for the PDH and dither schemes are 9.9×10(-10) cm(-1) and 5.3×10(-9) cm(-1), respectively.