Repetition Rate Fluctuations Research Articles

High-average-power 216 MHz Kerr lens mode-locked Yb:KGW ring laser oscillator for application to laser spectroscopy

We report the development of a ring Yb:KGW laser oscillator with an average power of 4.22 W, a pulse duration of 312 fs at a repetition rate of 216 MHz. The ring laser oscillator is purely Kerr lens mode-locked (KLM) taking advantage of the high nonlinear refractive index of the laser crystal in spite of being pumped by a multimode laser diode. To the best of our knowledge, this is the highest average power obtained from a KLM ring Yb:KGW laser oscillator. Monitoring the repetition rate fluctuations after initial warm-up of the laser cavity, a peak to valley of only 354.28 Hz during 30 min of free-running operation has been achieved. This could make a free-running ring cavity a suitable light source for application to laser spectroscopy. Using the ring laser oscillator, we have measured the absorption of the second overtone of the ν1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u _1$$\\end{document} mode of NH3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}. We have also measured absorption spectra of the Yb:KGW crystal to evaluate the quality of the crystal affected by the doped impurities.

Rapid Repetition Rate Fluctuation Measurement of Soliton Crystals in a Microresonator.

Temporal solitons have attracted great interest in the past decades for their behavior in a steady state, where the dispersion is balanced by the nonlinearity in a propagation Kerr medium. The development of dissipative Kerr solitons (DKSs) in high-Q microcavities drives a novel, compact, chip-scale soliton source. When DKSs serve as femtosecond pulses, the repetition rate fluctuation can be applied to ultrahigh precision metrology, high-speed optical sampling, and optical clocks, etc. In this paper, the rapid repetition rate fluctuation of soliton crystals (SCs), a special state of DKSs where particle-like solitons are tightly packed and fully occupy a resonator, is measured based on the well-known delayed self-heterodyne method. The SCs are generated using a thermal-controlled method. The pump is a frequency fixed laser with a linewidth of 100 Hz. The integral time in frequency fluctuation measurements is controlled by the length of the delay fiber. For a SC with a single vacancy, the repetition rate fluctuations are ~53.24 Hz within 10 µs and ~509.32 Hz within 125 µs, respectively.

Synchronization Maintenance of Synchronized Time-Lens Source in the Presence of Repetition Rate Drift of the Mode-Locked Laser for Coherent Raman Scattering Microscopy

Synchronized time-lens source can be synchronized to mode-locked lasers and has emerged as a new solution for two-color synchronized laser source. It has found widespread applications in coherent Raman scattering microscopy. Relative timing jitter between the synchronized time-lens source and the mode-locked laser is the key parameter for estimating the synchronization performance. Recently, it has been demonstrated theoretically that if the repetition rate of the mode-locked laser fluctuates around a mean value, then the relative timing jitter is only a fraction of the intrinsic timing jitter of the mode-locked laser. However, in some practical mode-locked laser systems, the repetition rate may also suffer from directional drift. Whether the time-lens source can be synchronized to such mode-locked lasers remains unknown. Here, we establish a physical model to account for both the directional repetition rate drift and the stochastic repetition rate fluctuation of the mode-locked laser, and demonstrate detailed numerical simulation results of the relative timing jitter in such synchronized systems. Our results indicate that various forms of repetition rate drift lead to an increase in the relative timing jitter compared with the drift-free case. However, the relative timing jitter is still smaller than the stochastic repetition rate fluctuation of the mode-locked laser when there is no drift, under practical experimental conditions. This suggests that the synchronized time-lens source is still a robust solution for two-color synchronized laser source.

Spectral distortion of dual-comb spectrometry due to repetition rate fluctuation**Project supported by the State Key Laboratory of Precision Measurement Technology & Instruments of Tsinghua University and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61205147).

Dual-comb spectrometry suffers the fluctuations of parameters in combs. We demonstrate that the repetition rate is more important than any other parameter, since the fluctuation of the repetition rate leads to a change of difference in the repetition rate between both combs, consequently causing the conversion factor variation and spectral frequency misalignment. The measured frequency noise power spectral density of the repetition rate exhibits an integrated residual frequency modulation of 1.4 Hz from 1 Hz to 100 kHz in our system. This value corresponds to the absorption peak fluctuation within a root mean square value of 0.19 cm−1 that is verified by both simulation and experimental result. Further, we can also simulate spectrum degradation as the fluctuation varies. After modifying misaligned spectra and averaging, the measured result agrees well with the simulated spectrum based on the GEISA database.

On the origin of flicker noise in carrier-envelope phase stabilization.

The origin of a 1/f noise contribution in the long-term carrier-envelope phase (CEP) measurements of mode-locked lasers is discussed. Using two different collinear interferometers for the out-of-loop characterization of feed-forward stabilized Ti:sapphire oscillators, we suppress a possible technical origin of 1/f noise to the extent possible. Both measurements indicate a lower limit of CEP frequency noise of 1 mHz/√Hz. Investigating several possible origins of this noise floor, we find a good agreement with a quantum noise mechanism that is directly induced by intracavity-amplified spontaneous emission (ASE). These findings enable direct access to ASE noise in short-pulse oscillators, which is very hard to characterize via repetition rate fluctuations. Finally, we discuss the possible consequences for frequency-comb-based timekeeping and frequency metrology, as well as for attosecond science.

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Repetition rate stabilization of the SBS Q-switched fiber laser by external injection

Repetition rate fluctuation is one of the main drawbacks of the low-threshold stimulated Brillouin scattering (SBS) Q-switched fiber laser. A method to stabilize the repetition rate is proposed in this paper by injecting a square-wave modulated light. It is measured experimentally that variance of the repetition rate can be improved from ~20% to ~1% of the period. It is also found that effectiveness of the method depends on modulation frequency and duty cycle of the injection. Its working mechanism is analyzed qualitatively.

Highly stable and efficient KTP-based intracavity optical parametric oscillator with a diode-pumped passively Q-switched laser

We present in this paper a highly stable and efficient KTP-based intracavity optical parametric oscillator with a diode-end-pumped Nd:YVO4/Cr:YAG passively Q-switched laser. At the incident diode pump power of 4 W, the signal (1.57 μm) and idler (3.29 μm) average output powers up to 580 and 100 mW, respectively, have been achieved. The corresponding conversion efficiency from the input diode pump power to the output signal power is 14.5%, while that to the total OPO output (signal+idler) reaches 17%. To the best of our knowledge, these are the highest conversion efficiencies reported to date. After more than four hours of investigation, the OPO power stability better than 2% has been obtained. In addition, efficient cavity dumping of the IOPO has inevitably led to the short pulse duration (1.6 ns) and high peak power output (8.3 kW) at the signal wave. Additionally, the amplitude and repetition rate fluctuations of the signal pulses are well within 5%.

Experimental study of noise properties of a Ti:sapphire femtosecond laser.

The fidelity of a coherent link between optical and microwave frequencies is largely determined by noise processes in a mode-locked femtosecond laser. This work presents an experimental study of the noise properties of a Ti:sapphire femtosecond laser. It includes measurements of pulse repetition rate fluctuations and shot noise exhibited by the Ti:sapphire femtosecond laser. Based on the results of noise measurements, the fractional frequency stability of a microwave signal produced by the femtosecond laser has been evaluated.