Pulse Shaping Mechanism Research Articles

Self-mode-locking of Ti:sapphire lasers: a matrix formalism

An extension of the ray-pulse matrix formalism is presented that includes self-phase-modulation, self-focusing, bandwidth limitations, and Gaussian apertures. With this more complete set of matrices it is shown how selfmode-locked lasers can be modeled and how the different pulse-shaping mechanisms interact in order to provide a stable femtosecond output.

High-power ultrafast laser diodes

Several ultrafast optical pulse generation techniques utilizing external cavity semiconductor lasers are described. These techniques include active mode locking, passive mode locking, hybrid mode locking, and several chirp compensation techniques. Utilizing these techniques, optical pulses of 200 fs in duration with over 160 W of peak power have been generated, making these pulses both the shortest and most intense ever generated with a semiconductor injection diode laser system. These pulses have been used to study the ultrafast amplification characteristics of semiconductor lasers. The results presented reveal the nature of the effects which dominate the pulse shaping mechanisms in external cavity hybrid mode-locked diode lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Subpicosecond pulse propagation on coplanar waveguides: experiment and simulation

Experimental results are presented concerning subpicosecond pulse propagation on normal metal, coplanar transmission line structures. The pulse distortion that occurs is modeled using a semiempirical curve fit to the full-wave analysis for the modal dispersion and quasi-static approximations for the conductor and radiation loss. Without using any adjustable parameters, very good agreement is obtained for the delay, rise time, and amplitude of the pulse for various propagation distances. For terahertz-bandwidth pulses on lines similar to the one studied, the modal dispersion and radiation losses are the dominant pulse-shaping mechanisms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Amplification of femtosecond optical pulses using a double confocal resonator

We experimentally examine a class of multipass amplifiers based on an open double confocal resonator. A preamplifier provides a gain of 800. An intermediate-stage amplifier produces pulse energies of 2 microJ for only 1.4 W of pump power at a repetition rate of 10 kHz. A third structure, which includes a four-prism sequence, provides on each pass adjustable forms of the four basic pulse-shaping mechanisms of saturable gain, saturable absorption, group-velocity dispersion, and self-phase modulation, as well as spectral filtering. This latter structure also reversibly lengthens the pulse duration in the gain medium from 50 fsec to over 450 fsec.

Colliding pulse mode-locked dye laser stabilization using an intracavity spectral filter

A trivial modification to the six-mirror CPM laser enhances the utility of the laser through the increased stability and allows for some limited spectral tuning. This modification may well be applicable to any CPM laser in which the SPM and GVD are such that there is a soliton-like pulse-shaping mechanism.

Ultrashort pulse propagation, pulse breakup, and fundamental soliton formation in a single-mode optical fiber

The propagation of ultrashort (0.83 ps), intense dye laser pulses through a single-mode optical fiber is investigated. The input wavelength is tuned in the vicinity of the zero dispersion wavelength of the fiber. Although the input power is sufficient to generate solitons of up to the tenth order we do not observe the formation of high-order solitons. Instead, the input pulse breaks up temporally and spectrally after an initial stage of narrowing, and an ultrashort Stokes pulse is formed which shifts continuously to lower frequencies with increasing fiber length. The parameters of this pulse closely correspond to those of the fundamental soliton solution of the nonlinear Schroedinger equation. Using fiber lengths from a few meters up to 1 km the resulting pulse durations lie between 55 and 410 fs and the corresponding wavelengths between 1.36 and 1.54 μm. Numerical simulations solving a modified nonlinear Schroedinger equation including higher order dispersion and the Raman effect are in good agreement with the experimental results. It is shown that the principal soliton pulse shaping mechanisms are pulse narrowing and the soliton self-frequency shift.

On the generation of temporally shaped laser pulses for inertial confinement

Pulse shaping of some form is likely to be essential for laser fusion. The problems encountered in amplifying such pulses in present-day laser systems are studied in a computer model. Saturation effects in the amplifiers can significantly alter the input pulse shape. This pulse shape modification sets in when the output flux in the final amplifier reaches ≈ 15% of the saturation flux. Consequently, great flexibility is required for the pulse shaping mechanism if pulses of complex shapes are to be obtained at the output of a large laser amplifier systems. The problems have been simulated and analyzed for one beam line of the University of Rochester's planned 24 beam phosphate glass laser systems.

Traveling-Wave Tube Nanosecond Pulse Generator In 24-Gc Region

A 24-Gc traveling-wave tube of the type ECL-1180 /24W80 was used for generating nanosecond carrier pulses. The helix of the traveling-wave tube was modulated by a 40-Mc high voltage sine wave. Duration, power and carrier frequency shift of the output RF pulse were examined quantitatively with respect to the modulating voltage. It was found that the delay time of a traveling-wave tube has a large effect on the characteristics of the output pulse. The theory of transmission line modulators was developed to explain the pulse shaping mechanism in the traveling-wave tube. Observations of output pulses were made with three measuring devices, i.e., video-sampling oscilloscope with crystal detector, interferometer, and spectrum analyzer. The interferometer was found to be useful for measuring half-amplitude duration of carrier pulse. Output pulses with half-amplitude duration of as short as 1 nsec were observed.