Bai Nie

Pulse generation without gain-bandwidth limitation in a laser with self-similar evolution

With existing techniques for mode-locking, the bandwidth of ultrashort pulses from a laser is determined primarily by the spectrum of the gain medium. Lasers with self-similar evolution of the pulse in the gain medium can tolerate strong spectral breathing, which is stabilized by nonlinear attraction to the parabolic self-similar pulse. Here we show that this property can be exploited in a fiber laser to eliminate the gain-bandwidth limitation to the pulse duration. Broad (∼200 nm) spectra are generated through passive nonlinear propagation in a normal-dispersion laser, and these can be dechirped to ∼20-fs duration.

Generation of 42-fs and 10-nJ pulses from a fiber laser with self-similar evolution in the gain segment

A double-clad Yb-doped all-normal-dispersion fiber laser with a narrow intra-cavity spectral filter is demonstrated to produce 22 nJ pulses at 42.5 MHz repetition rate. These pulses are characterized and compressed via mulitphoton intrapulse interference phase scan to as short as 42 fs and 10 nJ/pulse. Adaptive compression underlies the achievement of 250-kW peak power, which enables efficient second and third harmonic generation with spectra spanning 30 nm and 20 nm, respectively.

Multimodal microscopy with sub-30 fs Yb fiber laser oscillator

Nonlinear optical microscopy with sub-30 fs pulses from an Yb-fiber laser, approximately three times shorter than typical fiber laser pulses, leads to an order of magnitude brighter third harmonic generation imaging. Multiphoton fluorescence, second and third harmonic generation modalities are compared on stained microspheres and unstained biological tissues.

Energy scaling of Yb fiber oscillator producing clusters of femtosecond pulses

Abstract. A Yb fiber oscillator producing high-energy femtosecond pulse clusters is reported. Visualized by averaging autocorrelation, the output pulses consist of femtosecond pulse clusters that appear as a picosecond envelope with a ∼100-fs pulse in its center. Using more than 200-m fiber, the pulse energy is scaled up to 450 nJ. This high energy in a cluster of femtosecond pulses enables an important application—laser-induced breakdown spectroscopy.

Anomalous laser-induced group velocity dispersion in fused silica

We present 20fs(2) accuracy laser-induced group velocity dispersion (LI-GVD) measurements, resulting from propagation of a femtosecond laser pulse in 1mm of fused silica, as a function of peak intensity. For a 5.5 × 10(11) W/cm(2) peak intensity, LI-GVD values are found to vary from -3 to + 15 times the material GVD. Normal induced dispersion can be explained by the Kerr effect, but anomalous LI-GVD, found when the input pulses have negative pre-chirp, cannot. These findings have significant implications regarding self-compression and the design of femtosecond lasers.

An Ultrafast Fiber Laser with Self-Similar Evolution in the Gain Segment

Techniques that use optical pulses extending from the picosecond to the attosecond have become an important adjunct to nanoscale science.

High-power femtosecond fiber lasers based on self-similar pulse evolution

The status of femtosecond fiber lasers based on self-similar evolution of parabolic pulses will be reviewed, and ongoing efforts to generate few-cycle pulses from fiber lasers will be described.

Multiphoton imaging with sub-30 fs Yb fiber laser

An Yb fiber laser oscillator with sub-30 fs pulses compressed by MIIPS is tested for multiphoton microscopy. It leads to greatly improved third harmonic generation images. Multiphoton fluorescence, second and third harmonic generation modalities are compared on stained microspheres and unstained biological tissues.

THG microscopy imaging of blood using sub-50fs Yb fiber laser

We report on multimodal imaging of blood using sub-50 fs pulses centered at 1060 nm wavelength. We find that red blood cells appear dark on SHG images while on THG images of blood provide bright signal and good contrast.

Towards a compact fiber laser for multimodal imaging

We report on multimodal depth-resolved imaging of unstained living Drosophila Melanogaster larva using sub-50 fs pulses centered at 1060 nm wavelength. Both second harmonic and third harmonic generation imaging modalities are demonstrated.