Versatile single-shot background-free pulse duration measurement technique,for pulses of subnanosecond to picosecond duration

An extension of the noncollinear second-harmonic generation technique for pulse autocorrelation measurements is described. A diffraction grating is used to produce a tailored, expanded beam, with a differential time delay along its expanded axis. When this beam is combined with an inverted replica of itself at the frequency-doubling crystal, the monitored spatial profile of the generated second-harmonic beam gives directly the duration of the incident laser pulse. A time resolution of better than 1 ps is obtained at 500 nm, and a total measurement range of∼80 ps. The optical system here described enables the extension of the measurement range in a simple manner.     

Rapid pulse shaping with homodyne detection for measuring nonlinear optical signals

We have designed a common-mode interferometric acousto-optic pulse shaper that is capable of shaping individual pulses differently from a mode-locked laser. The design enables the measurement of weak nonlinear optical signals such as two-photon absorption and self-phase modulation at megahertz rates. The experimental apparatus incorporates homodyne detection as a means of resolving the phase of the detected signals. The fast data acquisition rate and the ability to perform measurements in scattering media make this experimental apparatus amenable to imaging applications analogous to measurements of two-photon fluorescence using a mode-locked laser.     

Pulsed homodyne measurements of femtosecond squeezed pulses generated by single-pass parametric deamplification

A new scheme is described for the generation of pulsed squeezed light by use of femtosecond pulses that have been parametrically deamplified through a single pass in a thin (100-microm) potassium niobate crystal with a significant deamplification of approximately -3 dB. The quantum noise of each pulse is registered in the time domain by single-shot homodyne detection operated with femtosecond pulses; the best squeezed quadrature variance was 1.87 dB below the shot-noise level. Such a scheme provides a basic resource for time-resolved quantum communication protocols.     

Direct shaping of picosecond high energy deep ultraviolet pulses

We demonstrate temporally shaped pulses in the deep ultraviolet spectral range (270 nm) with energies up to 37 μJ using an efficient prism stretcher and an acousto-optic programmable dispersive filter (AOPDF) applied directly in the UV. The scheme allows for arbitrary phase and amplitude shaping of picosecond UV pulses at high energy in a simple and efficient way.     

From femtosecond infrared to picosecond visible pulses: temporal shaping with high-efficiency conversion

We present a single-pass frequency doubler that efficiently converts broadband near-infrared femtosecond pulses into narrow-spectrum visible picosecond pulses. An optimal control technique is introduced for properly designing aperiodically poled nonlinear crystals to generate visible pulses of the desired amplitude, phase profile, and carrier wavelength.     

单发次皮秒脉冲对比度的三阶自相关法测试技术

为了测试单发次皮秒脉冲对比度,设计并研制了非共轴三阶自相关仪。三阶自相关仪参数优化设计中,在确保获得正确的相关耦合信号的前提下,充分利用KDP晶体的极化张量,寻找有效非线性系数相对较高的相位匹配点,在满足非共线相位匹配条件的同时兼顾群速匹配,为增大时间测试范围,选取较大的入射光夹角。采用分区测试和图形重构技术,增大对比度测试的动态范围,结果显示采用两个科学级CCD测试的脉冲对比度在105左右。     

单发次皮秒脉冲对比度的三阶自相关法测试技术

为了测试单发次皮秒脉冲对比度,设计并研制了非共轴三阶自相关仪。三阶自相关仪参数优化设计中,在确保获得正确的相关耦合信号的前提下,充分利用KDP晶体的极化张量,寻找有效非线性系数相对较高的相位匹配点,在满足非共线相位匹配条件的同时兼顾群速匹配,为增大时间测试范围,选取较大的入射光夹角。采用分区测试和图形重构技术,增大对比度测试的动态范围,结果显示采用两个科学级CCD测试的脉冲对比度在105左右。     

Efficient generation of narrow-bandwidth picosecond pulses by frequency doubling of femtosecond chirped pulses

We demonstrate efficient generation of picosecond narrow-bandwidth pulses by frequency mixing of broadband opposite chirped pulses in a type I doubling crystal. This procedure allows us to produce picosecond pulses that are perfectly synchronized with femtosecond pulses. The experiment shows a decrease of the initial bandwidth by a factor of more than 30, while a high conversion efficiency is maintained.     

Ground-state recovery of coumarin dyes by pump-probe technique with picosecond pulses

Rotation-free transmission measurements governed by ground-state recovery of coumarin 102, coumarin 138 and coumarin 339 dyes in ethanol solutions were performed for the first time by pump-probe technique using 35 ps pulses of Nd:YAG laser at 355 nm. Recovery of absorption is characterized by simple exponential behaviour with relaxation times of 4.0, 3.7 and 3.0 ns respectively for C 102, C 138 and C 339. These values are comparable to the lifetimes of the first excited singlet states.     

A new technique to study dielectric breakdown with picosecond laser pulses

With ultrashort light pulses at high intensity, a sharp increase of second harmonic generation is observed in various media presenting direct evidence for a large carrier concentration produced by dialectric breakdown. In water, signals up to 10⁸ photons at the second harmonic frequency are measured and compared with model calculations, which suggest an electron density of ～ 10²⁰ cm^-3. Breakdown is found to occur at power levels notably higher than inferred from the ocular observation of broad band luminescence.     

Comments on the picosecond pulse width measurement by the single-shot second harmonic beam technique

We show that the measurement of the ultrashort light pulse duration by the single-shot second harmonic beam technique requires caution. It is found that the far-field distribution of the second harmonic radiation from non bandwidth-limited pulses shows a pronounced structure even if the near-field pattern is without structure. This interference effect is interpreted as being due to the special symmetry properties of the spatial coherence of the second harmonic beam. A simple method for a quick determination of the existence of the bandwidth-limited relation in an individual picosecond light pulse is proposed.     

Direct linear measurement of ultrashort light pulses with a picosecond streak camera

The durations of ultra-short (4–7 psec) laser pulses have been directly measured with an image tube streak camera designed for time resolution in the picosecond region. The camera was calibrated with simultaneously recorded two photon fluorescence pulse profiles and it is shown that a time resolution limit of ≈1 psec should be possible with this system.     

Synthesis of fractal light pulses by quasi-direct space-to-time pulse shaping

We demonstrated a simple diffractive method to map the self-similar structure shown in squared radial coordinate of any set of circularly symmetric fractal plates into self-similar light pulses in the corresponding temporal domain. The space-to-time mapping of the plates was carried out by means of a kinoform diffractive lens under femtosecond illumination. The spatio-temporal characteristics of the fractal pulses obtained in this way were measured by means of a spectral interferometry technique assisted by a fiber optics coupler (STARFISH). Our proposal allows synthesizing suited sequences of focused fractal femtosecond pulses potentially useful for several current applications, such as femtosecond material processing, atomic, and molecular control of chemical processes or generation of nonlinear effects.     

Generation and measurement of frequency-tunable picosecond pulses from dye lasers

Experimental techniques for the generation of frequency-tunable picosecond pulses from passively mode-locked dye lasers are reviewed. Direct photoelectric measurements of pulse durations with a streak-camera of time resolution <3 ps are described. Recent studies of the build-up of pulse shortening and of saturable absorber photochemistry are discussed and related to the mode-locking processes in dye lasers.     

Efficient preparation of a four-photon cluster state with homodyne measurement via cross-Kerr nonlinearity

A scheme is proposed for generating a multiphoton entangled cluster state among four modes. The scheme only uses Kerr medium, beam splitter and homodyne measurements on coherent light fields, which can be efficiently made in quantum optical laboratories. The photon in the signal mode is prepared in a superposition state of the vacuum state and one-photon state while the probe beam is initially set in a coherent state superposition. The strong probe mode interacts successively with multiple signal-mode photo...     

Intraband carrier kinetics and picosecond pulse shaping in field-enhanced bulk semiconductor absorbers

Picosecond pulse propagation through a field-enhanced waveguide bulk semiconductor saturable absorber is studied numerically. Fast switching from unsaturated absorption to delayed strong saturation and gain, as well as the predicted dependence of saturation energy on electric field, is based on intraband carrier kinetics and electric-field dynamics in the absorber and can lead to improved, controllable pulse shaping.     

Stabilization,attenuation and shaping of picosecond laser pulses by two-photon absorption in dyes

The attenuation of ultrashort laser pulses by two-photon absorption is theoretically described when a dye is used as the absorbing medium. It is shown that two-photon absorption also yields an intensity stabilization of low repetition rate laser emissions without a significant loss of power. Consequently this technique is proposed for pulse attenuation and stabilization near the damage threshold of second harmonic generator crystals, and its performance is theoretically compared with other attenuation methods.     

Diffraction grating single-shot correlation system for measurement of picosecond laser pulses

We study and experimentally demonstrate a sensitive single-shot correlation system in which only a diffraction grating is used to produce a transverse time delay (TTD) in the reference pulse.The mechanism of the TTD introduced by the grating and the formation of the relative time delay (RTD) in the noncollinear correlation system are analyzed in detail.By using our system,we successfully measured the temporal duration of picosecond laser pulses,and a time resolution of ～0.047 ps is obtained at 1047 nm.The impact of the grating dispersion and the second harmonic beam walk-off effect on the measurement are considered.     

Coherence time measurement of picosecond pulses by a light-induced grating method

The temporal coherence function |Γ(τ)| of picosecond pulses from a Nd: YAG laser has been measured by diffraction at a transient grating. The coherence timet _c =7 ps is small compared to the pulse widtht _p =22 ps but is in correspondence with the spectral bandwidth Δv=12·10¹⁰ Hz. The new method for measuring the coherence function |Γ(τ)| is discussed and compared with a previous experiment.