Chung-Po Huang

Generation of 11-fs pulses from a self-mode-locked Ti:sapphire laser

By optimizing the intracavity dispersion compensation in a self-mode-locked Ti:sapphire laser, we have generated pulses of 10.95-fs duration. Dispersion within the laser cavity is reduced by use of a short 4.5-mm highly doped Ti:sapphire crystal and fused-silica prisms. The output from the laser has an average power of as much as 500 mW, with a wavelength centered at 780 nm and a bandwidth of 62 nm. Our results demonstrate that the exceptionally broad bandwidth of Ti:sapphire can be utilized to generate pulses that, to our knowledge, are shorter than has been possible with any other type of laser material to date.

Pulse evolution in a broad-bandwidth Ti:sapphire laser.

We demonstrate that by operating near the zero second- and third-order dispersion point in a self-mode-locked Ti:sapphire laser we can generate sub-10-fs pulses. Our numerical simulations show that the pulse duration is limited by fourth-order dispersion and that shorter pulses will be possible if this can be reduced. Also, by inserting a pellicle in various positions in a Ti:sapphire cavity, we have measured the intracavity pulse duration and chirp of the circulating pulse in the laser. Our results demonstrate that the pulse is shortest near the middle of the laser crystal, in one direction of propagation. In the other direction of propagation, the pulse is positively chirped and several times longer.

Amplification of 26-fs, 2-TW pulses near the gain-narrowing limit in Ti:sapphire

We report the generation of 26-fs-duration pulses, with an energy of 60 mJ, from a simple multipass Ti:sapphire amplifier system. The peak power of our amplified pulses is 2 TW, and the repetition rate is 10 Hz. Our amplifier design consists of two highly doped multipass amplifiers and is simple and compact. We use an all-reflective, low-groove-density grating stretcher and compressor, combined with a relatively short material path length in the amplifier. This design allows us to minimize higher-order dispersion. The result is a laser system that generates multiterrawatt transform-limited pulses, with good beam quality and low amplified-spontaneous-emission levels, at a duration near the theoretical limit imposed by gain narrowing in Ti:sapphire.

17-fs pulses from a self-mode-locked Ti:sapphire laser

We have generated sub-17-fs-duration pulses directly from a self-mode-locked Ti:sapphire laser. These pulses are near transform limited, with a wavelength centered at 817 nm, a pulse repetition rate of 80 MHz, and an average power of 500 mW. By minimizing the amount of material inside the laser cavity and choosing the correct glass for the intracavity prism pair, third-order dispersion in the laser can be significantly reduced compared with that in previous designs. Extracavity compensation for group-velocity dispersion in the output coupler and autocorrelator optics is necessary to measure this pulse width. To our knowledge this laser generates pulses substantially shorter than any other laser to date.

Ti:sapphire amplifier producing millijoule-level, 21-fs pulses at 1 kHz

We have developed a Ti:sapphire amplifier system capable of producing pulses of 1 mJ, with 20-22-fs pulse duration, at a 1-kHz repetition rate. The amplifier has a unique design consisting of a three-mirror multipass ring configuration with a highly doped Ti:sapphire crystal as the gain medium. Pulses of 15-fs duration from a Ti:sapphire oscillator are temporally stretched and injected into the amplifier, which is an eight-pass system with a total gain of 10(6). The amplif ier is more than 10% efficient, and the shot-to-shot energy fluctuation of the output is less than 2%. The output beam focuses to 1.8 times the diffraction limit.

Generation of 21-fs millijoule-energy pulses by use of Ti:sapphire

We have demonstrated the generation of 21 ± 2 fs duration pulses, with an energy of 0.5 mJ, a bandwidth of 44 nm, and a repetition rate of 10 Hz, using a chirped-pulse amplification scheme in Ti:sapphire. We use 11-fs, 5-nJ pulses from a Ti:sapphire oscillator as the input for an eight-pass Ti:sapphire amplifier. A broadband, low-dispersion chirped-pulse stretcher-and-amplifier design was used for propagation and amplification of the ultrashort pulses. By the addition of a prism pair to the stretcher, both the second- and third-order dispersions are minimized, permitting us to generate near-transform-limited amplified pulses at a duration near the theoretical limit imposed by gain narrowing in Ti:sapphire.

Fourth-order dispersion-limited solitary pulses

We analyze the performance of a Ti:sapphire self-mode-locked laser with near-zero second- and third-order dispersion. Our simulations show that, in the presence of fourth-order dispersion, solitary laser pulses can be supported within a wide parameter range, close to the experimental values of these parameters. We also conclude that it is possible to generate pulses much shorter than 10 fs if fourth-order dispersion is further reduced.

Generation of transform-limited 32-fs pulses from a self-mode-locked Ti:sapphire laser

We show that near-transform-limited 32-fs pulses can be generated directly from a self-mode-locked titanium-doped sapphire oscillator. The laser operates at a center wavelength of 813 nm with a bandwidth of 22 nm in a TEM00 mode. Correct choice of the glass for the intracavity prism pair results in improved compensation of group-velocity dispersion, which yields near-transform-limited output pulses. Compensation for group-velocity dispersion in the output coupler and autocorrelator optics is necessary in order to measure this transform-limited pulse width.

Space-time focusing of femtosecond pulses in a Ti:sapphire laser

We present what is to our knowledge the first three-dimensional model of a femtosecond pulse propagating in a Ti:sapphire laser crystal, which includes dispersion, self-focusing, and finite response time of the medium and does not assume the slowly varying envelope approximation. The combined action of material dispersion and phase modulation leads to a dramatic space-time focusing on the pulse. Dispersion prevents catastrophic selffocusing and self-steepening of the pulse, even though the peak power of the pulse is much greater than the critical power for self-focusing filamentation. Extrapolation of these results to shorter-pulse durations shows that this space-time focusing mechanism can operate even for pulses with durations close to the response time of the Kerr nonlinearity.

Amplification of 26 fs, 2 TW pulses in Ti:sapphire

We have demonstrated a simple multipass amplifier system that generates pulses as short as 26 fs in duration, with an energy of > 60 mJ per pulse. The design minimizes higher-order dispersion and spectral distortions, and results in a near-transform limited 2 TW peak power output.