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Frequency combs present a unique tool for high-precision and rapid molecular spectroscopy. Difference frequency generation (DFG) of near-infrared sources is a common approach to generate passively stabilized mid-infrared combs. However, only little attention has been paid so far to precisely measure the coherence properties of such sources. Here, we investigate these using a Raman-soliton based DFG source driven by an Yb:fiber frequency comb. A heterodyne beat between the second harmonic of the phase-locked DFG comb near 4 µm and a 2 µm Tm:fiber frequency comb locked to the same optical reference is performed. Using this method, we measure the relative phase noise power spectral density of both combs. This results in a sub-Hz relative linewidth between the DFG comb and the Tm:fiber comb. We also introduce a new pump/seed delay locking mechanism based on interferometry for long-term stable intensity noise suppression.

Optics express 31(8), 12880 (2023). doi:10.1364/OE.486338, Published by Optica, Washington, DC

Photonics research 10(10), 2309 - 2316 (2022). doi:10.1364/PRJ.465883, Tailoring the properties of the driving laser to the need of applications often requires compromises among laser stability, high peak and average power levels, pulse duration, and spectral bandwidth. For instance, spectroscopy with optical frequency combs in the extreme/visible ultraviolet spectral region requires a high peak power of the near-IR driving laser, and therefore high average power, pulse duration of a few tens of fs, and maximal available spectral bandwidth. Contrarily, the parametric conversion efficiency is higher for pulses with a duration in the 100-fs range due to temporal walk-off and coating limitations. Here we suggest an approach to adjust the spectral characteristics of high-power chirped-pulse amplification (CPA) to the requirements of different nonlinear frequency converters while preserving the low-phase-noise (PN) properties of the system. To achieve spectral tunability, we installed a mechanical spectral shaper in a free-space section of the stretcher of an in-house-developed ytterbium-fiber-based CPA system. The CPA system delivers 100 W of average power at a repetition rate of 132.4 MHz. While gaining control over the spectral properties, we preserve the relative-intensity-noise and PN properties of the system. The high-power CPA can easily be adjusted to deliver either a spectrum ideal for mid-IR light generation (full width at half maximum of ∼11 nm, compressed pulse duration of 230 fs) or a spectrum ideal for highly nonlinear processes such as high-harmonic generation (−10 dB level of >50 nm, transform-limited pulse duration of ∼65 fs)., Published by Optica, Washington, DC

We report on 100-W 132 MHz Yb:fiber amplifier seeded by a low noise oscillator. We tune the laser spectrum to match it to different applications while keeping noise properties and power performance of the system.

OSA continuum 4(6), 1889 - 1896 (2021). doi:10.1364/OSAC.424340, We present a comparison of two low-noise carrier-envelope offset (CEO) frequency stabilization methods studied using an ytterbium (Yb) fiber laser oscillator based on a nonlinear amplifying loop mirror. We first investigate the phase locking performance achieved with cross-gain modulation (XGM) via injection of an auxiliary low-power continuous-wave (CW) laser into the fiber gain medium. Amplification of the injected CW laser light cross-modulates the gain of the oscillator, resulting in an intra-cavity power modulation, thus providing control of the CEO frequency. The XGM method is then compared with the conventional pump-current modulation scheme. Both stabilization methods provide similar locking performances with sub-200-mrad of integrated residual carrier-envelope-phase (CEP) noise (10 Hz to 1 MHz), suitable for high-resolution comb spectroscopy applications., Published by OSA, Washington, DC

We demonstrate an all-PM fiber integrated femtosecond Yb NALM oscillator with 88 fs compressed pulse duration and sub-fs free-running timing jitter [25 kHz to 5 MHz].

We demonstrate a 41.6 MHz, 1.3 ps, 140 pJ Ho:fiber oscillator centered at 2050 nm for seeding Ho:YLF amplifiers. RIN and timing jitter of the oscillator are characterized while comparing two commercial Tm pump lasers.

We demonstrate a 41.6 MHz, 1.3 ps, 140 pJ Ho:fiber oscillator using a nonlinear amplifying loop mirror (NALM) as saturable absorber. The oscillator is constructed entirely with polarization-maintaining (PM) fibers, is tunable with a center wavelength between 2035 nm and 2075 nm, and can be synchronized to an external RF reference. For our application of Ho:YLF amplifier seeding for dielectric electron acceleration, the laser is tuned to 2050 nm and synchronized to a stable RF reference with 45 fs rms timing jitter in the integration interval [10 Hz, 1 MHz]. We show long term synchronized operation and characterize the relative intensity noise (RIN) and timing jitter of the oscillator for two different Tm-fiber pump lasers.

9th EPS-QEOD Europhoton Conference, virtual (Prague), Czech Republic, 30 Aug 2020 - 4 Sep 2020, Prague, Czech Republic, 30 Aug 2020 - 4 Sep 2020; The European physical journal / Web of Conferences 243, 04002 (2020). doi:10.1051/epjconf/202024304002, We present first results on a Ho: fiber oscillator based on a Nonlinear Amplifying Loop Mirror (NALM) configuration, intended for seeding a Ho: YLF regenerative amplifier. The NALM technique, when using polarization-maintaining (PM) fibers, allows self-starting, low noise, alignment-free, robust long term stable operation. It is implemented here–to the best of our knowledge–for the first time using a Ho-fiber without Tm co-doping., Published by EDP Sciences, Les Ulis

We present a flexible figure-9 Yb: fiber-laser and investigate the impact of intra-cavity group delay dispersion on amplitude/phase noise. We show that the free-running carrier-envelope-offset frequency short-term linewidth can range from several MHz to

We demonstrate a fully integrated alignment free, femtosecond Yb:fiber laser operating in the stretched pulse regime. After compression, the laser provides a long-term stable output of 104 fs pulses at 76 MHz repetition rate.

Photoacoustic imaging is based on the detection of generated acoustic waves through thermal expansion of tissue illuminated by short laser pulses. Fiber lasers as an excitation source for photoacoustic imaging have recently been preferred for their high repetition frequencies. Here, we report a unique fiber laser developed specifically for multiwavelength photoacoustic microscopy system. The laser is custom-made for maximum flexibility in adjustment of its parameters; pulse duration (5–10 ns), pulse energy (up to 10 μJ) and repetition frequency (up to 1 MHz) independently from each other and covers a broad spectral region from 450 to 1100 nm and also can emit wavelengths of 532, 355, and 266 nm. The laser system consists of a master oscillator power amplifier, seeding two stages; supercontinuum and harmonic generation units. The laser is outstanding since the oscillator, amplifier and supercontinuum generation parts are all-fiber integrated with custom-developed electronics and software. To demonstrate the feasibility of the system, the images of several elements of standardized resolution test chart are acquired at multiple wavelengths. The lateral resolution of optical resolution photoacoustic microscopy system is determined as 2.68 μm. The developed system may pave the way for spectroscopic photoacoustic microscopy applications via widely tunable fiber laser technologies.

We demonstrate a low-noise carrier-envelope-offset frequency stabilized all-PM Yb:fiber oscillator. Two different stabilization methods lead to sub 200 mrad integrated fo phase noise (10 Hz to 1 MHz), suitable for comb spectroscopy applications. © 2019 The Author(s)