Donald J. Harter

Chirped-pulse amplification of 100-fsec pulses

Chirped-pulse amplification is used to generate 2-mJ pulses of 106-fsec duration in an alexandrite amplifier. Compression of the optical pulse is achieved by using a sequence of intracavity prisms in conjunction with diffraction gratings. This allows for the compensation of both linear and quadratic contributions to the dispersion from the amplifier.

Portable terahertz system and its applications

Industrial applications of THz techniques require compact and reliable systems. We have designed and constructed two portable THz systems integrated with femtosecond, erbium- doped fiber lasers. Terahertz emitters based on photoelectron-transport and optically-rectification were tested in the system. With the use of a 10-mW laser pump beam, the signal-to-noise ratio of the system is greater than 5,000. We studied THz beam generation and detection with two different laser wavelengths. Under the consideration of group velocity matching, the frequency response of the THz system is calibrated. Our portable systems have been applied for the coherent measurement of the refractive index and dielectric constant of polymer thin films, which will play an important role in the ongoing quest for higher speeds in integrated circuits. The measurement is based on a comparison of THz phases with and without the film. The refractive index of thin film can be derived according to the phase difference. The system has sufficient sensitivity to perform these measurements on films as thin as 10 microns. We have also used one of these systems for THz measurements of molecular rotation spectra in air/vapor mixtures.

Wavelength tunable alexandrite regenerative amplifier

We describe a wavelength tunable alexandrite regenerative amplifier which is used to amplify nanosecond slices from a single-frequency cw dye laser or 50-ps pulses emitted by a diode laser to energies in the 10-mJ range. The amplified 5-ns slices generated by the cw-pumped line narrowed dye laser are Fourier transform limited. The 50-ps pulses emitted by a gain-switched diode laser are amplified by more than 10 orders of magnitude in a single stage.

Short pulse amplification in tunable solid state materials

We describe our work on the amplification of short pulses in tunable solid state materials; specifically alexandrite and Ti:sapphire. Our goal is to amplify femtosecond range pulses to the joule level in a table top size laser. We will describe our results which show that such a laser is now feasible.

Alexandrite-laser-pumped Cr3+ : LiSrAlF6

Alexandrite pumping of Cr3+:LiSrAlF6 (Cr:LiSAF) is investigated by studying the most probable limiting parameters, including gain, optical damage, and heat load capacity. An alexandrite-pumped, 200-mJ, Q-switched Cr:LiSAF oscillator–amplifier has been demonstrated.

Fiber lasers in ultrafast optics

The current status of ultrafast fiber lasers is discussed. Recent advances in optical fiber designs as well as improved saturable absorbers have greatly improved the performance and the reliability of ultrafast fiber oscillators. Equally significant have been improvements in ultrafast fiber amplifier designs and compact chirped pulse amplification systems in conjunction with chirped periodically-poled LiNbO3, which now allow the manufacture of compact ultrafast fiber laser systems that can exceed the performance of conventional ultrafast lasers based on bulk optics. The unique size advantage of fiber lasers opens up the field of ultrafast optics to novel OEM-type applications. For example ultrafast fiber lasers have been successfully employed as subsystems in all-optical time delay scanning, for two-photon microscopy as well as for THz pulse generation.

High-power compact ultrafast fiber lasers

High-power compact ultrafast pulse sources based on optical fiber lasers are discussed. The optical efficiency of fiber- based ultrafast pulse sources is optimized by the implementation of double-clad Yb-doped fibers. The spatial limitations of ultrafast single-mode fiber lasers and amplifiers are overcome by the implementation of diffraction-limited multi-mode rare-earth-doped fibers, allowing for the generation of ultrafast pulses with large peak powers. In the temporal domain, a further increase in obtainable peak powers is made possible by the use of chirped pulse amplification or the amplification of pulses with parabolic temporal profiles. Parabolic pulses are generated in the asymptotic limit in high gain fiber amplifiers operating in the positive dispersion regime.

Generation and Amplification of High-Peak-Power Femtosecond Pulses in Ti:Al2O3/Alexandrite and Ti:Al2O3/Nd:Glass Systems

We present recent developments in tunable femtosecond oscillators and amplifiers using Ti:Al2O3. These systems produce gigawatt pulses at wavelengths compatible with large Alexandrite or glass amplifiers.