Misalignment-free, Kerr-lens-modelocked Yb:Y2O3 2.2-GHz oscillator, amplified by a semiconductor optical amplifier.

We present a fully bonded, misalignment-free, diode-pumped Yb:ceramic (Yb:Y2O3) oscillator producing 190-fs pulses at a repetition frequency of 2.185 GHz. Self-starting Kerr-lens-modelocked operation was obtained from both outputs of the ring cavity with an average combined output power of 14-30 mW for pump powers from 380-670 mW. The fully bonded design provided self-starting, turnkey operation, with a relative intensity noise of 0.025% from 1 Hz-1 MHz. Tuning of the pulse repetition rate over a 120 kHz range was demonstrated for a 2°C change in temperature. Chirped-pulse amplification in a semiconductor optical amplifier was shown to increase the pulse average power to 69 mW and the pulse energy (peak power) from 2.5 pJ (12 W) to 32 pJ (71 W).

Towards a space-qualified Kerr-lens mode-locked laser.

We report a 1.5-GHz Kerr-lens mode-locked (KLM) Yb:Y2O3 ring laser constructed by directly bonding the cavity components onto an aluminum baseplate. Stable unidirectional operation with an output power ≥10mW was obtained for pump-diode currents of 300-500 mA, corresponding to a total electrical power consumption of 1.5 W. After repetition rate stabilization, a comparison with a conventionally constructed identical laser showed a 50% reduction in phase noise. In free-running operation the bonded laser showed superior passive repetition rate stability. The bonding process follows an already proven integration approach in space-borne instrumentation, mapping a development pathway for KLM lasers in aerospace applications.

The Rydberg constant and proton size from atomic hydrogen.

At the core of the "proton radius puzzle" is a four-standard deviation discrepancy between the proton root-mean-square charge radii (rp) determined from the regular hydrogen (H) and the muonic hydrogen (µp) atoms. Using a cryogenic beam of H atoms, we measured the 2S-4P transition frequency in H, yielding the values of the Rydberg constant R∞ = 10973731.568076(96) per meterand rp = 0.8335(95) femtometer. Our rp value is 3.3 combined standard deviations smaller than the previous H world data, but in good agreement with the µp value. We motivate an asymmetric fit function, which eliminates line shifts from quantum interference of neighboring atomic resonances.

(87)Rb-stabilized 375-MHz Yb:fiber femtosecond frequency comb.

We report a fully stabilized 1030-nm Yb-fiber frequency comb operating at a pulse repetition frequency of 375 MHz. The comb spacing was referenced to a Rb-stabilized microwave synthesizer and the comb offset was stabilized by generating a super-continuum containing a coherent component at 780.2 nm which was heterodyned with a (87)Rb-stabilized external cavity diode laser to produce a radio-frequency beat used to actuate the carrier-envelope offset frequency of the Yb-fiber laser. The two-sample frequency deviation of the locked comb was 235 kHz for an averaging time of 50 seconds, and the comb remained locked for over 60 minutes with a root mean squared deviation of 236 kHz.

650-nJ pulses from a cavity-dumped Yb:fiber-pumped ultrafast optical parametric oscillator.

Sub-250-fs pulses with energies of up to 650 nJ and peak powers up to 2.07 MW were generated from a cavity-dumped optical parametric oscillator, synchronously-pumped at 15.3 MHz with sub-400-fs pulses from an Yb:fiber laser. The average beam quality factor of the dumped output was M2 ~1.2 and the total relative-intensity noise was 8 mdBc, making the system a promising candidate for ultrafast laser inscription of infrared materials.

Wavelength stabilization of a synchronously pumped optical parametric oscillator: optimizing proportional-integral control.

We describe a formal approach to the wavelength stabilization of a synchronously pumped ultrafast optical parametric oscillator using proportional-integral feedback control. Closed-loop wavelength stabilization was implemented by using a position-sensitive detector as a sensor and a piezoelectric transducer to modify the cavity length of the oscillator. By characterizing the frequency response of the loop components, we constructed a predictive model of the controller which showed formally that a proportional-only feedback was insufficient to eliminate the steady state error, consistent with experimental observations. The optimal proportional and integral gain coefficients were obtained from a numerical optimization of the controller model that minimized the settling time while also limiting the overshoot to an acceptable value. Results are presented showing effective wavelength and power stabilization to levels limited only by the relative intensity noise of the pump laser.