Showing papers on "Femtosecond pulse shaping published in 1988"

High-resolution femtosecond pulse shaping

Abstract: The synthesis of arbitrarily shaped femtosecond pulses by spectral filtering in a temporally nondispersive grating apparatus is demonstrated. Spectral filtering is accomplished by utilizing spatially patterned masks to modify the amplitude and the phase of the optical frequency components that are spatially dispersed within the apparatus. We are able to pattern spectra over a large dynamic range (approaching 104) and with unprecedented resolution. We illustrate the power of this technique by synthesizing a number of femtosecond waveforms, including femtosecond tone bursts with terahertz repetition rates, picosecond square pulses with 100-fsec rise times, and highly complex pseudonoise bursts produced by spectral phase encoding.

Optical systems and methods based upon temporal stretching, modulation and recompression of ultrashort pulses

Abstract: A communications systems is characterized by a pulse-shaping technique for producing shaped, stabilized, ultra-short (picosecond to femtosecond) pulses containing encoded information Pulse shaping is accomplished by temporally stretching and chirping an ultra-short pulse from a pulse generator, modulating the pulse in real time and temporally compressing the pulse in a manner so as to cancel the original chirp

Femtosecond ultraviolet pulse generation in β‐BaB2O4

Abstract: Intracavity doubling in β‐BaB2 O4 (BBO) of femtosecond pulses into the ultraviolet with high efficiency is reported. Pulse widths down to 43 fs at a 108 Hz repetition rate and outputs as high as 20 mW per arm of the femtosecond laser on a continuous‐wave basis can be achieved. The ultraviolet pulse widths were determined through detailed cross‐correlation measurements based on sum‐frequency mixing to 210 nm in ultrathin BBO crystals.

Femtosecond optical pulse amplification

Abstract: A number of techniques have been developed for amplification of optical pulses of approximately 100-fs duration. These amplifiers span a wide range of operating parameters from kilowatt to gigawatt peak powers and from 10 Hz to megahertz repetition rates. Amplification of femtosecond pulses has also been demonstrated at several wavelengths including visible, near-infrared, and ultraviolet regions. Several problems arise when amplifying short optical pulses to very high intensities. The problems are discussed and the state of the art of femtosecond optical pulse amplification is reviewed. >

Self-, cross-, and induced-phase modulations of ultrashort laser pulse propagation

Abstract: Spectral broadenings of picosecond and femtosecond pulses arising from self-phase modulation, cross-phase modulation, induced-phase modulation, and induced spectral broadening in condensed matter are reviewed. The spectral broadening of the Raman line produced in an optical fiber is compared to the spectral width of the pump-laser line as evidence for cross-phase modulation. Induced-phase modulation of a weak picosecond 527-nm laser pulse in BK-7 glass occurred in the presence of an intense picosecond 1054-nm laser pulse. The induced spectral broadening about a weak nonphase-matched second-harmonic pulse at 527 nm is observed by propagating an intense primary 1054-nm picosecond laser pulse through ZnSe crystals. >

Femtosecond Ultraviolet Pulse Generation in β-BaB 2 O 4

Abstract: Almost all current results on ultrafast processes are derived from femtosecond lasers in the visible or near infrared. There is a clear need to extend the wavelength range of high repetition rate femtosecond pulses into the ultraviolet (uv). Frequency doubling (SHG), both extra1- and intracavity2, represents one technique for generating such pulses. However, the results achieved so far have been far short of what have been achieved in the visible. In this talk, we report an intracavity doubling experiment using the new nonlinear optical crystal β-BaB2O4 (BBO) that results in nearly complete recovery of the normal visible fundamental output power in the form of femtosecond uv pulses at the second harmonic. Recent success in our laboratory in growing and fabricating high quality BBO crystals3 has enabled us to generate the shortest uv pulses reported so far, less than 45 fs at 315 nm.

Effects of pulse shaping in laser spectroscopy and nuclear magnetic resonance

Abstract: Pulsed excitation fields are routinely used in most laser and nuclear magnetic resonance (NMR) experiments. In the NMR case, constant amplitude (rectangular) pulses have traditionally been used; in laser spectroscopy the exact pulse shape is often unknown or changes from shot to shot. This article is an overview of the effects of radio-frequency and laser pulse shapes and the instrumental requirements for pulse shaping. NMR applications to selective excitation, solvent suppression, elimination of phase roll, and reduced power dissipation are discussed, as are optical applications to soliton generation, velocity selective excitation, and quantitative population transfer.

Fast dephasing processes studied with a femtosecond coherent Raman system

Abstract: Synchronous pumping of a femtosecond and a tunable picosecond dye laser provides synchronized trains of ultrashort pulses at variable frequency difference. The system allows the authors to study coherently excited Raman transitions with femtosecond time resolution. Fast dephasing processing with decay times of a few hundred femtosecond are measured. >

Method and apparatus for generating ultrashort light pulses

Abstract: A method and apparatus for generating a light pulse having a duration as short as about 3 picoseconds is disclosed A 5 mJ 25 picosecond second harmonic light pulse from a Nd:YAG laser system is focused into a 5 cm cell filled with D2 O so as to generate a continuum light pulse spanning about 150 nanometers with an average energy of at least 20 nd/nm across the spectrum The continuum light pulse is fed through a 10 nanometer narrowband filter centered at 580 nanometers, producing an output pulse having a duration of about 3 picoseconds The pulse so produced has a number of uses including as a seed pulse for dye laser oscillators and solid state amplifiers or as a pump source for pumping ultrashort dye lasers

Pulses of Four Optical Cycles from an Optimized Optical Fibre/Grating Pair/Soliton Pulse Compressor at 1·32 μm

Abstract: In this Letter, we report on the generation of pulses as short as 18 fs by means of an optimized two-stage optical fibre-grating pair and high-order soliton-effect pulse compressor. These are the shortest pulses yet reported in the near-infrared spectral region and correspond to four optical cycles at 1·32 μm.

Dynamic theory of picosecond optical pulse shaping by gain-switched semiconductor laser amplifiers

Abstract: A dynamic theory of semiconductor laser amplifiers is developed that takes into account the coherent time-dependent amplification of an incident optical pulse as well as the nonlinear dynamics of the semiconductor laser when driven be an unbiased injection-current pulse. For suitable time delays between the optical and the electrical pulse, a strongly nonlinear self-induced shortening of the emitted laser pulse is predicted. >

Pulse Asymmetry in the Colliding-pulse Mode-locked Dye Laser

Abstract: The design and performance characteristics of a group velocity dispersion-compensated colliding-pulse passively mode-locked ring dye laser are discussed. Pulses as short as 19 fs have been observed and analyses of experimental autocorrelations—both intensity and interferometric—together with spectral data that show evidence of pulse asymmetry are presented.

Study of a linear femtosecond laser in passive and hybrid operation

Abstract: Astigmatism compensation and stability of a linear mode-locked femtosecond dye laser is analysed. Hybrid and passive mode-locking operation of the astigmatic compensated cavity is discussed. A direct study of the colliding pulse effect is made.

Coherent propagation of intense ultrashort laser pulses in a molecular multilevel medium

Abstract: The Maxwell–Schrodinger equations describing the ultrashort laser pulse propagation in multilevel molecular media are shown to be analytically solvable and to reduce to nonlinear multisine‐Gordon equations for certain models of the field–molecule system. Special cases of level schemes are shown to lead to soliton propagation. A numerical study is presented in order to examine the effect of nonresonant (virtual) transitions on pulse propagation and amplification in a three‐level molecular system as a function of intensity and detuning.The Maxwell–Schrodinger equations describing the ultrashort laser pulse propagation in multilevel molecular media are shown to be analytically solvable and to reduce to nonlinear multisine‐Gordon equations for certain models of the field–molecule system. Special cases of level schemes are shown to lead to soliton propagation. A numerical study is presented in order to examine the effect of nonresonant (virtual) transitions on pulse propagation and amplification in a three‐level molecular system as a function of intensity and detuning.

Generation of synchronized ultraviolet and red femtosecond pulses by intracavity frequency doubling

Abstract: An ultraviolet femtosecond pulse train of milliwatt average power and 100-MHz repetition rate is extracted from a colliding-pulse mode-locked dye laser by intracavity frequency doubling in KDP crystal. The ultraviolet and visible outputs, which are comparable in power and pulse duration, are perfectly synchronized with each other. >

Ultrashort pulse reshaping with a nonlinear Fabry–Perot cavity matched to a train of short pulses

Abstract: Reshaping of ultrashort pulses is predicted to occur when a pulse train from a mode-locked laser is incident upon a nonlinear Fabry–Perot cavity whose length is matched to the period of the pulse train. The temporal shape of the transmitted pulses depends on the relaxation time of the nonlinearity of the Kerr medium inserted into the Fabry– Perot cavity. When the pulse duration is shorter than the Kerr relaxation time, considerable pulse narrowing (by factors of 101–103) is predicted. If the Kerr relaxation time is longer than the period of the pulse train, the analysis shows the existence of two temporal shapes of the output pulse, leading to the possibility of bistability between these two states. A Kerr nonlinearity with an instantaneous response can be used to generate square output pulses. Both the transient and the permanent regimes are investigated, and analytical expressions for the narrowing factors are found.

Real time processing of picosecond and femtosecond laser pulses: Application to free‐electron lasers

Abstract: An original and reliable technique, based on a three‐wave interaction, has been designed and successfully tested to analyze the evolution of the modes and the pulse length of a free‐electron laser during the buildup of the radiation. The technique was developed in order to study the effects of the optical guiding in the free‐electron laser built at Stanford and driven by the MARK III linear accelerator. We explicitly mention that this technique can be easily exploited to monitor, in real time, the pulse‐to‐pulse fluctuations of the mode size and the pulse length of the pulses delivered by any laser independently of its pulse length from femtosecond to millisecond.

The pulse die laser: Its use at 577 nm wavelength

Abstract: The ability to increase laser-induced cutaneous blood vessel damage selectivity is dependent upon optimizing various intrinsic laser parameters. Varying the laser emission wavelength, pulse duration, and/or incident energy dosage allows the clinician potential improvement in the laser treatment of cutaneous small blood vessel processes such as port-wine hemangioma and telangiectasia. The pulsed dye laser at 577 nm and a pulse duration of 300 to 400 microseconds, incorporates desired laser parameters into its design. Clinical evaluation of the therapeutic outcome with this laser reveals favorable results while significantly minimizing potential adverse side effects.

Stimulated Raman Scattering and Self-phase Modulation of Ultrashort Light Pulses in Optical Fibres

Abstract: Stimulated Raman scattering of picosecond pulses in optical fibre is investigated, with account taken of pulse walk-off by group velocity dispersion, pump depletion and chirp production by the intensity-dependent refractive index. An analytical solution of the basic equation is given by which the characteristic parameters of the Stokes and pump pulses, such as pulse half-width, intensity, mid-frequency and chirp, are calculated. It is shown that the chirp of the Stokes pulse does increase faster than that of the pump pulse with increasing fibre length and may surpass it by nearly three times after the pulse walk-off.

Single shot measurement of the optical Kerr effect kinetics

Abstract: We present a method allowing measurement of the kinetics of the optical Kerr effect in transparent media using a single femtosecond pulse. This method is based on a spectrotemporal transformation. We describe the experimental results obtained for ultrafast and noninstantaneous responses.

Geometrical limitations in grating pair pulse compression

Abstract: Optical-pulse compression using gratings has become a standard technique for producing ultrafast pulses outside a laser cavity. Short pulses produced by a mode-locked laser are focused into an optical fiber. There, self-phase modulation and group velocity dispersion act to broaden the bandwidth of the pulse and impart to it a negative chirp. A pair of diffraction gratings are placed following the fiber. Different frequencies follow different paths through the grating pair; if they are properly oriented, the gratings can compensate for the linear chirp of the pulse. In this way the spectral components of the pulse are compressed in time. The net effect of the system is to produce an output pulse that is shorter than the input pulse because of the additional frequencies generated in the fiber.

Optical pulse waveform shaper

Abstract: An optical pulse waveform shaper capable of providing an optical pulse waveform of a desired intensity distribution with little loss. The optical pulse beam split by a beam splitter is directed into the beam splitter with a phase difference to combine with the transmitted optical pulse beam. The phase difference is controllable. The optical pulse waveform shaper is applicable between a laser oscillator with different exciting conditions and an amplifier.

Quasi-linear ring colliding-pulse mode-locked femtosecond laser using binary energy-transfer gain dye mixture

Abstract: A new method for femtosecond pulse generation using a binary energy-transfer dye mixture for the gain medium in a novel linear ring colliding-pulse mode-locked dye-laser configuration is reported Pulses of 30-fsec duration and 187-nm spectral width are routinely generated

Reduction of bit error rate in high speed optical transmission systems due to optimized electrical drive pulse shaping

Abstract: The optical pulse shape and the spectral characteristics of a laser diode are improved by optimized electrical drive pulse shaping. A reduction of the bit error rate in a 2.24 Gbit/s system is measured.

Short optical pulse generator having a looped directional coupler external cavity

Abstract: A short optical pulse generator is disclosed in which the optical radiation from a driven laser diode (101) is coupled to an external cavity which includes a looped directional coupler (104, 120) which reflects a portion of the optical radiation back to the laser causing the laser to mode-lock and produce an output which consists of a stream of very short high repetition optical pulses. By changing the length of the loop (107), the repetition rate of the pulse stream can be varied and by adjusting the coupling coefficient of the coupler either mechanically or electrooptically, the pulse width and pulse height parameters of the pulse stream can be varied.