M. C. Stumpf

Diode-pumped gigahertz femtosecond Yb:KGW laser with a peak power of 3.9 kW

We present a diode-pumped Yb:KGW laser with a repetition rate of 1 GHz and a pulse duration of 281 fs at a wavelength of 1041 nm. A high brightness distributed Bragg reflector tapered diode laser is used as a pump source. Stable soliton modelocking is achieved with a semiconductor saturable absorber mirror (SESAM). The obtained average output power is 1.1 W and corresponds to a peak power of 3.9 kW and a pulse energy of 1.1 nJ. With harmonic modelocking we could increase the pulse repetition rate up to 4 GHz with an average power of 900 mW and a pulse duration of 290 fs. This Yb:KGW laser has a high potential for stable frequency comb generation.

Fully stabilized optical frequency comb with sub-radian CEO phase noise from a SESAM-modelocked 1.5-µm solid-state laser

We report the first full stabilization of an optical frequency comb generated from a femtosecond diode-pumped solid-state laser (DPSSL) operating in the 1.5-μm spectral region. The stability of the comb is characterized in free-running and in phase-locked operation by measuring the noise properties of the carrier-envelope offset (CEO) beat, of the repetition rate, and of a comb line at 1558 nm. The high Q-factor of the semiconductor saturable absorber mirror (SESAM)-modelocked 1.5-µm DPSSL results in a low-noise CEO-beat, for which a tight phase lock can be much more easily realized than for a fiber comb. Using a moderate feedback bandwidth of only 5.5 kHz, we achieved a residual integrated phase noise of 0.72 rad rms for the locked CEO, which is one of the smallest values reported for a frequency comb system operating in this spectral region. The fractional frequency stability of the CEO-beat is 20‑fold better than measured in a standard self-referenced commercial fiber comb system and contributes only 10(-15) to the optical carrier frequency instability at 1 s averaging time.

Effect of the carrier-envelope-offset dynamics on the stabilization of a diode-pumped solid-state frequency comb.

We investigate the dynamics of the carrier-envelope-offset (CEO) frequency, f(CEO), controlled by a pump current on the self-referencing of an optical frequency comb generated from a diode-pumped solid-state laser at 1.56 μm. We observe a reversal point in the tuning of f(CEO) with the pump current. Between the low- and high-frequency region in the dynamic response of f(CEO) to pump current modulation, we observe a significant phase shift of ≈180 deg in the transfer function. As a result, it is impossible to stabilize f(CEO) at a pump current above the reversal point, although the free-running CEO beat at this point has a higher signal-to-noise ratio than underneath the reversal point at which the locking is straightforward. Our results indicate that a high signal-to-noise ratio and a low-noise CEO beat are not sufficient indicators for the feasibility of comb self-referencing in cases for which CEO dynamics play a dominant role.

Compact Er:Yb:glass-laser-based supercontinuum source for high-resolution optical coherence tomography

We present a low coherence light source by direct super-continuum generation from a diode-pumped, passively modelocked Er:Yb:glass-laser, which generates 198 fs transform-limited pulses with an average power of 100 mW at a repetition rate of 75 MHz. The pulse train is launched into a dispersion optimized highly nonlinear fiber for spectral broadening. The optical bandwidth spans from 1150 nm to 2400 nm, which is more than one octave. The potential for ultrahigh-resolution optical coherence tomography (OCT) is demonstrated by coherence measurements supporting an axial resolution of 3.5 microm in air.

Fiber-Broadened Passively Modelocked Er: Yb: Glass Laser for High-Resolution Optical Coherence Tomography

We demonstrate a low coherence light source by directly launching the output of a femtosecond diode-pumped modelocked Er:Yb:glass laser into a highly-nonlinear fiber. The measured interferogram supports a depth resolution of 4 mum in air.

Compact Gigahertz Frequency Comb Generation: How Short Do The Pulses Need To Be?

We investigate the required pulse duration for coherent supercontinuum generation for CEO detection in the 1-µm and 1.5-µm spectral regime. We demonstrate the first self-referenceable frequency comb from a gigahertz diode-pumped solid state laser.

First fully stabilized frequency comb from a SESAM-modelocked 1.5-µm solid-state oscillator

In conclusion, we have demonstrated the first fully stabilized frequency comb generated by an ultrafast Er:Vb:glass laser. The SESAM-modelocked, diode-pumped laser uses a high-Q cavity which results in low-noise operation. A coherent, octave-spanning SC is generated by nonlinear spectral broadening in a polarization maintaining highlynonlinear fiber. We observe a more than 10-times improvement in the free-running CEO frequency linewidth compared to free-running femtosecond fiber laser systems operating in this spectral region. The CEO frequency and the repetition rate are stabilized to the same 10-MHz external reference over hours. The Allan deviation of the 20-MHz CEO reaches 10-8 at 1-s with an H-maser as an external reference and a stable locked operation of more than 11 hours was achieved in a preliminary long-term evaluation. A CEO-beat signal can still be observed at a large reduction of the pump power, resulting in a reduced intracavity pulse energy and in an increased pulse duration up to 260 fs. We expect that this result will have a significant impact for the future development of more compact stable frequency combs as the relatively long pulse duration relaxes the requirements on the modelocked laser. This will become even more important for gigahertz pulse repetition rates.

Low-noise near-infrared optical frequency comb from a femtosecond diode-pumped solid state laser

Following the demonstration of the first fully stabilized solid state laser frequency comb operating in the 1.5-µm spectral region [1,2], we present a detailed analysis of the noise properties of this comb and show its superior noise performances compared to a commercial fiber-laser comb stabilized using similar feedback electronics. Our comb is based on a ∼200-fs Er:Yb:glass laser oscillator (ERGO) generating ∼90 mW average output power, pumped by 600 mW from a 980-nm telecom-grade laser diode. The ERGO laser generates a coherent octave-spanning frequency comb in a 1.5-m long dispersion-flattened, polarization-maintaining, highly nonlinear fibre without any additional amplification. The ∼40-mW average power supercontinuum is polarized, stable, and was optimized for a strong carrier envelope offset (CEO) frequency signal. The CEO-beat, detected in a standard f-to-2f interferometer [3], is 49 dB above the noise floor in a 100-kHz resolution bandwidth and has the narrowest linewidth (3.6 kHz) of a free-running CEO achieved in the 1.5-µm spectral region. Full comb stabilization is obtained by phase-locking both the CEO and the repetition rate to the same 10-MHz local reference. Feedback is applied to a piezo-transducer controlling the cavity length to lock the repetition rate to frep = 75 MHz and to the pump diode current to lock the CEO-beat to |fCEO|=20 MHz.

Optical frequency comb with sub-radian CEO phase noise from a SESAM-modelocked 1.5-μm solid-state laser

The noise properties of a fully stabilized 1.5-μm diode-pumped solid-state laser frequency comb are analyzed. The locked CEO-beat has an integrated phase noise of ~0.75 rad and the optical carrier stability is 5x10-13 at 1 sec.

First CEO Frequency Measurement of a SESAM-Modelocked 1.5-µm Solid-State Laser Oscillator

We present a self-referencable frequency comb by optimized octave-spanning supercontinuum generation of a diode-pumped 170-fs Er:Yb:glass-laser with 110 mW power. The f-to-2f CEO frequency has 49-dB signal-to-noise and >10-times narrower bandwidth than free-running 1.5-µm fiber-systems.