Oscar Eduardo Martinez

Negative dispersion using pairs of prisms.

We show that pairs of prisms can have negative group-velocity dispersion in the absence of any negative material dispersion. A prism arrangement is described that limits losses to Brewster-surface reflections, avoids transverse displacement of the temporally dispersed rays, permits continuous adjustment of the dispersion through zero, and yields a transmitted beam collinear with the incident beam.

Direct determination of the amplitude and the phase of femtosecond light pulses.

A direct measurement of the amplitude and the phase of a femtosecond light pulse is performed for the first time to our knowledge. The measurement is made in the frequency domain, and the time dependence of the field can be easily obtained by a Fourier transform. The technique relies on a pulse synthesis scheme to unravel the frequency dependence of the phase. A mask filters the spectrum, which gives rise to a pulse with a measurable temporal profile related to the frequency dependence of the phase. In particular, with a rectangular slit the time delay of the synthesized pulse is the first derivative of the phase with respect to the frequency of the original pulse at the central frequency of the filter. The amplitude of the spectrum is obtained from the power spectrum.

Grating and prism compressors in the case of finite beam size

The grating and prism compressors are studied for the case of finite beam size by using the Kirchhoff–Fresnel integral and an amplitude transfer operator for the grating and prism. The results show that, even for well-collimated beams, pulse broadening may occur (mainly because of the wavelength dependence of the lateral walk-off). Methods to avoid the different types of distortions appearing in these systems are discussed.

Pulse distortions in tilted pulse schemes for ultrashort pulses

Abstract Analytical expressions are found for the propagation of the amplitude of tilted ultrashort pulses. The distortions arising are the pulse broadening, tilt angle decrease, chirp, frequency shift and spatial profile variation. Expressions for these quantities are found and it is shown that the mechanisms responsible for the distortions are the group velocity dispersion and the spectral lateral walkoff. The conditions to be met in order to avoid such distortions are derived.

Theory of passively mode-locked lasers including self-phase modulation and group-velocity dispersion

Closed-form analytical solutions are obtained for a passively mode-locked laser for the case in which self-phase modulation and group-velocity dispersion, in addition to the more conventional mechanisms of saturable absorption and gain, shape the laser pulses. Provided that the self-phase modulation and group-velocity dispersion are related in a manner similar to that which causes soliton formation in optical fibers, this additional pulse shaping can reduce the pulse duration below the limit otherwise set by the laser bandwidth.

Design of high-power ultrashort pulse amplifiers by expansion and recompression

A system that expands and recompresses an ultrashort pulse by means of diffraction gratings is described. The expansion can be large enough to broaden the pulse to several nanoseconds. In this manner, as the signal and pump pulses have similar lengths, high-efficiency amplifiers can be designed. The expansion avoids inefficient energy storage in high-gain amplifiers and nonlinear effects in the amplifier medium, and the amplified spontaneous emission is drastically reduced by working in a saturated amplifier regime.

Matrix formalism for pulse compressors

A matrix formalism for grating and prism compressors is introduced. It is an extension of the standard ABCD matrix formalism for Gaussian optics, but includes the possibility of considering dispersive elements such as gratings and prisms. The full formation on the frequency-dependent phase shift is obtained to compute the time delay dispersion. The formalism simplifies the design of compressors with focusing optics. Information on beam divergence and astigmatism is also acquired. >

Analysis of a method of phase measurement of ultrashort pulses in the frequency domain

A detailed analysis of a method of phase measurement of ultrashort light pulses is performed. It is shown that the output pulse of a zero dispersion compressor with a mask consisting of a narrow slit is a wide pulse delayed an amount equal to the phase derivative of the field spectrum with respect to frequency. State criteria to determine whether the approximations are valid are presented. The method is not affected by artifacts coming from diffraction effects in the slit or by the fact that only correlations are measured. The effects of the errors in positioning the elements are considered and minimized in the construction of the experimental apparatus. A novel technique for measurement of the derivative of the cross correlation is described, and it is used to locate the delayed output pulse. >

Characterization of a liquid crystal television as a programmable spatial light modulator

The properties of a liquid crystal television to be used as a spatial modulator of the polarization of a laser beam are studied. It is found that the model most commonly used for the display description does not adequately reproduce the transmission through crossed polarizers. A new model is proposed that takes into account additional birefringence effects resulting from border effects near the television windows. With this correction, the anomalous behavior of the television is explained and the throughput for different configurations is properly predicted.

Spatial–temporal analysis of the self-mode-locked Ti: sapphire laser

We employ our extended spatial–temporal matrices to analyze the Ti: sapphire self-mode-locked laser. Our results agree with previously reported experimental work and give us a deeper understanding of the way this laser functions. We found the pulse-shaping mechanism to be essentially solitonlike; the role of the aperture is to discriminate against cw operation. We also study the buildup of the pulse starting from a fluctuation.