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I demonstrate the closed-loop control of a programmable liquid-crystal spatial light modulator using real-time SHG FROG. Control theory states that proportional only controllers are almost never suitable for very tight control because any calibration errors can result in offsets between the input (desired result) and output. In this work, the pulse output from the real-time FROG software is sent to proportional-integral controller for maintaining the spectral phase of a pulse. The additional integral control term removes the constant offset that plagues proportional only controllers. The response time of pulse shaping system is a few seconds, limited only by the speed of the pulse shaper.

The present work deals with the investigation of the pulse shaper based on a shorted symmetrical strip line. It has been determined that the best balancing and minimum afterpulse oscillations are provided in the pulse shaper where at first short pulses are formed and then balancing of the output signal is performed. The best strobe pulse shaper is a shaper with ferrite that has a larger relative permeability. The suitable design of the line-balance converter for the 100 ps strobe pulse shaping was obtained.

We report on a computer-controlled pulse-shaper setup with high-efficiency throughput, based on dispersive prisms, as an alternative to the conventional grating ultrafast pulse-shaping apparatus. A detailed description of the experimental apparatus and operation of this system is given. The advantages and disadvantages of this configuration are discussed. Experimental implementation of the prism pulse shaper in recovering nearly bandwidth-limited laser pulses from chirped ultrafast laser pulses is demonstrated using both closed-loop and open-loop operation. © 2005 Society of Photo-Optical Instrumentation Engineers. 44 3 1 5 Cited By :1

Membres du jury : M. Alain Brun (directeur de thèse) M. Marc Brunel (rapporteur) M. Jean-Paul Chambaret M. Franck Falcoz M. Patrick Georges M. François Salin (rapporteur) M. Bruno Viana (Invité); This work deals with diode-pumped solid-state femtosecond lasers, based on new ytterbium-doped crystals, emitting around 1.06 µm. We study especially two recently discovered crystals: Yb3+: BOYS (or Yb3+: Sr3Y(BO3)3) and Yb3+: SYS (or Yb3+: SrY4(SiO4)3O) which crystallographic, physic and spectroscopic properties are well adapted to short-pulse generation and amplification (with duration typically from 10-14 to 10-12 s). To begin with, we developed two femtosecond oscillators based on Yb3+: BOYS and Yb3+: SYS, which produced 69-fs and 94-fs pulses, respectively, with an energy around 1 nJ and at a repetition rate of approximately 100 MHz. The oscillators' cavities were mode-locked in very stable regimes, and were self-started and stabilized by a semi-conductor saturable absorber mirror. Afterwards, in order to increase the energy of these pulses, we developed a regenerative amplifier based on Yb3+: SYS. This amplifier produced 380-fs pulses, with an energy of 70 µJ, at a repetition rate of 1 kHz. Finally, we used an acousto-optic programmable filter as a pulse shaper to increase the amplified pulses spectral bandwidth. These experimentations allowed us to validate a theoretical model that led to realistic numerical simulations of the Yb3+: SYS regenerative amplifier, and to improve the performances of the whole Yb3+: SYS femtosecond laser, so that pulses with less than 300-fs duration should be produced.; Les travaux exposés dans ce mémoire concernent le développement de lasers femtoseconde entièrement pompés par diodes, utilisant de nouveaux cristaux laser dopés à l'ytterbium, et émettant à une longueur d'onde proche de 1,06 µm. Nous étudions plus particulièrement deux cristaux récemment découverts : l'Yb3+: BOYS (ou Yb3+: Sr3Y(BO3)3) et l'Yb3+: SYS (ou Yb3+: SrY4(SiO4)3O), dont les propriétés cristallographiques, physiques et spectroscopiques sont particulièrement adaptées à la production et à l'amplification d'impulsions brèves (de durées typiques allant de 10-14 à 10-12 s). Dans un premier temps, nous avons réalisé deux oscillateurs femtoseconde basés respectivement sur l'Yb3+: BOYS et l'Yb3+: SYS, qui ont permis de produire des impulsions de durées respectives égales à 69 fs et 94 fs avec une énergie par impulsion de l'ordre du nanojoule, et à une cadence avoisinant la centaine de mégahertz. Le régime impulsionnel a été obtenu par verrouillage de modes passif, dont le démarrage automatique et l'excellente stabilité ont été assurés par un miroir absorbant saturable à semi-conducteur. Dans un deuxième temps, afin d'augmenter l'énergie de ces impulsions, nous avons développé un amplificateur régénératif basé sur l'Yb3+: SYS. Placé en aval d'un oscillateur femtoseconde Yb3+: SYS, cet amplificateur nous a conduit à la production d'impulsions d'une durée de 380 fs, ayant une énergie de 80 µJ, à une cadence de 1 kHz. Enfin, nous avons utilisé un filtre acousto-optique programmable pour modeler l'amplitude spectrale des impulsions qui sont issues de l'oscillateur femtoseconde puis injectées dans l'amplificateur régénératif. Ces expérimentations nous ont ouvert de nouvelles perspectives en validant un modèle théorique (qui a donné lieu à des simulations numériques réalistes de l'amplificateur régénératif), et en améliorant les performances de notre chaîne laser femtoseconde basée sur l'Yb3+: SYS de sorte que des impulsions d'une durée inférieure à 300 fs devrait être produites.

Summary from only given. We demonstrate the first operation of a direct space to time (DST) pulse shaper in the 1.55 /spl mu/m band, desirable for optical communications applications. Additionally we report the use of a phase-only diffractive optical element (DOE) for essentially loss-free spatial pattern generation at the input to the DST pulse shaper. Although phase-only filters are commonly used in the familiar Fourier transform pulse shaper, our current work constitutes the first application of phase-only filters for the DST pulse shaping configuration.

In this presentation, we will report results in realizing one of the most ubiquitous image processing operations, correlation of time-domain images by use of Fourier synthesis and a photorefractive quantum well (PRQW) as the holographic diffractive mask inside a pulse shaper.

A polarization line-by-line pulse shaper is used for generation and noniterative spectral phase retrieval of optical arbitrary waveforms (OAWs) spanning over the entire repetition period. The method is completely reference-free, making it particularly attractive in measuring high repetition-rate OAW.

We proposed a diagnostics to measure temporal and spatial profiles of ultrashort optical pulses based on spatial-spectral interferometry. With this measurement technique we directly observed space-time coupling at a Fourier pulse shaper.

We experimentally demonstrate the first programmable optical pulse compression to 6 fs using a prism-pair-formed pulse shaper with a spatial light modulator. This method manifests the potential to compress pulses to the one-cycle regime.

Analytical solutions for a direct space-to-time encoder are used to determine the output distortions and limitations that may appear, and the relevance of the design parameters in the quenching or avoidance of such distortions.

An integral part of the contemporary high-power laser system for inertial confinement fusion (ICF) research is a flexible pulse-shaping system that is able to produce a laser pulse temporal profile specified in advance and controlled to a high degree of accuracy.

We experimentally demonstrate automated coherent control of a photodissociation reaction as well as femtosecond pulse compression using a pulse shaper and an evolutionary algorithm with feedback.

Recent investigations of microcavity frequency combs based on cascaded four-wave mixing have revealed a link between the evolution of the optical spectrum and the observed temporal coherence. Here we study a silicon nitride microresonator for which the initial four-wave mixing sidebands are spaced by multiple free spectral ranges (FSRs) from the pump. Additional lines then fill in to yield a comb with single FSR spacing, resulting in partial coherence. By using a pulse shaper to select and manipulate the phase of various subsets of spectral lines, we are able to probe the structure of the coherence within the partially coherent comb. Our data demonstrate strong variation in the degree of mutual coherence between different groups of lines and provide support for a simple model of partially coherent comb formation. (C) 2012 Optical Society of America

A new pulse shaper is proposed for ultra-wideband applications. The pulse shaper consists of a third-order bandstop filter and a third-derivative Gaussian pulse generator. The bandstop filter is realised by means of a cascade of three newly proposed meandered V-sickle slotted ground structures. Experimental results reveal that the new design fully complies with the FCC emission mask and demonstrates high signal attenuation capability at the desired rejection band. The proposed pulse shaper also features compact size.

A novel optical-to-electrical technique for the generation of continuous periodic arbitrarily shaped millimetre-wave electromagnetic waveforms at centre frequencies of 50 GHz is demonstrated. Tailored optical pulse sequences from a novel direct space-to-time pulse shaper driving a high-speed photodiode enable generation of arbitrary phase- and frequency-modulated waveforms on a cycle-by-cycle basis.

A 160 Gbit/s all-optical wavelength converter with 3R-regenerating capability is demonstrated. The 3R-wavelength converter uses an optical decision gate based on ultrafast fibre nonlinearity to switch a 160 GHz pulse train by the incoming 160 Gbit/s data signal. A pulse shaper is implemented to reduce the detrimental effect of phase jitter in the decision gate and a fibre-based wavelength shifter for free allocation of the wavelength at the output.

A highly stable CAMAC pulse shaper is described. The pulse length is controlled from the CAMAC-dataway and can be changed in steps of about 3.5% from 20 ns to 150 μs. This single-width module operators in two modes: the “normal” mode and the “updating” one. The double pulse resolution of the “updating” mode is 20 ns.

A pulse-shortening device is described for use on pulsed thermal-neutron sources. The device employs rotating single crystals and has applications in the design of high-resolution cold-neutron spectrometers.

A pulse shaper has been constructed which will produce the standard nuclear weapon puise shape in the Natick Laboratories solar furnace. An array of 16 radial vanes, each about 1 1 2 M ft long, is placed in the converging beam about 40 in. in front of the focus. These vanes, driven at variable speed by a specially constructed cam, control the irradiance at the target. The device operates successfully to produce pulses corresponding to the range of weapons from 25 KT to the megaton range. Over this range of speeds there is some variation in shape, especially near the peak; the difficulty arises because of the very high accelerations needed to produce this shape. Also, at long times after the peak the shape deviates from the standard, giving an exposure of about 1·9 Hmtm instead of the desired 2·12 Hmtm where Hm is the maximum irradiance and tm the time to reach that irradiance.

An instrument is described that converts signals from photomultipliers into pulses of standard amplitude (10 mA) and adjustable width (2.5–100 ns). It consists of an input shaping network, of which two versions are given, and a tunnel diode cascade trigger circuit. An attempt has been made to reduce the time slewing to a minimum: with input pulses ranging from 10–160 mA, from a 56 AVP photomultiplier, it remains within ±0.25 ns. The instrument is capable of working up to frequencies of 150 Mc/sec.

Attenuators and a bipolar pulse shaper using the p-i-n diodes are described and short specifications are presented. Small-signal characteristics of the diode-twins were measured in the 30–900 MHz frequency range. The diode characteristics and some advantages of the p-i-n diode use in pulse circuits for nanosecond and sub-nanosecond range are discussed.

A new mode of operation of a tunnel-diode pair circuit has been developed and theory and circuit design are presented. Operation principles are discussed for damped-oscillation mode, unbalanced mode, and balanced mode with overdamping. Since the circuit has a high degree of freedom, several applications are possible, for example, as an inverter, pulse shaper, quasi-stable memory, and time-to-pulse width converter. The test circuit arrangement together with some experimental results are reported and characteristics of the different modes are discussed.

A simple and quick method to make an absolute time calibration of a time-to-pulse-height converter (TPHC) has been developed. The method is also suitable for quantitative determination of the differential linearity of a TPHC. In addition to ordinary laboratory instruments two fast gating systems and a simple TD pulse shaper are needed. The circuits are described in detail together with the overall system. The results of a linearity test of a commercial TPHC in two different conversion ranges are presented.

A ring counter with a resolution of 300 Mc is described. The circuit is reliable because of the counting code. A prototype of a decade counter (pulse shaper and flip-flop followed by the ring counter) has a resolution of 500 Mc.

A pulse shaper, which has a proper dead time of 9 ns, and which makes possible pulse counting up to 100 MHz independently of the nominal duration of the output pulse smoothly controlled within 5–20 ns, is described. The nominal sensitivity of the shaper is 100 mV, the range of its control is 50–350 mV. The electronic control of the duration of the output pulse and the threshold is provided.

The problem of reliably triggering the Crass 7F4 Tachograph is explained and a solution is proposed. Modifications to the 7P4 and the addition of an amplifier/pulse shaper are described, and an adjustment procedure is given.

A discriminator and pulse shaper is described with the following characteristics: 1 mA minimum threshold ranging up to 30 mA, maximum input repetition rate of 100 Megapulses/s for threshold variation within 5%; delay 4 ns at 1% overdrive, time slewing (for input pulse risetime 0.5 ns) is 2 ns for 80% and 4 ns for factor of 100 overdrive. At minimum threshold (0.5 mA) the circuit can be overdriven by at least a factor of 10, more for higher threshold settings. This has been obtained by input limitation and complete isolation of the output tunnel shaper during all the input pulse width.

The current vs. voltage characteristic of boron makes it possible to produce simple boron semiconductor devices which in principle act as contactless switches. The switching operation can be triggered by varying the current through the boron, the temperature of the boron, or the ambient temperature. Measurements of the current vs. voltage characteristic are reported. These characteristics and the possible operating points are also calculated under the assumption of a pure temperature effect. Various examples of circuits employing boron semiconductor devices are given.

We present an ultra-broadband optical parametric chirped-pulse amplification (OPCPA) system operating at 3.4 µm center wavelength with a peak power of 75 MW. The OPCPA system is split into a pre- and a power-amplifier stage. Both stages are based on apodized aperiodically poled MgO:LiNbO3 (APPLN). The collinear mixing configuration allows us to manipulate the spectral phase of the output mid-infrared pulses by sending the near-infrared seed pulses through a pulse shaper. The system delivers clean 75-fs pulses with record-high 700 mW average power, corresponding to 7 µJ of pulse energy at a repetition rate of 100 kHz.

A novel incoherent scheme for generation of direct-sequence binary biphase modulated ultrawideband (UWB) signals is proposed and experimentally demonstrated. There is no requirement for pulse shaper (optical filter) in our proposed system.

We demonstrate a novel method of phase-contrast CARS spectroscopy by using an optical bandpass filter and a mechanical modulator instead of a 4f pulse shaper used in previous studies. Our system has several advantages over the conventional one; the simplicity of the setup, a larger throughput, and the higher data rate of measurements. We use the known vibrational frequencies of chloroform to verify the efficacy of this method.

We demonstrate the possibility of creating user-defined partially coherent light pulses by means of a slight modification of the direct space-to-time pulse shaper. Specifically, we generate a mutual coherence function that corresponds to the independent-elementary-pulse representation model. The theoretical limits in the parameter of global coherence and the efficiency of the system are studied. Our result opens the door to a new way of quantum control in laser-assisted chemical reactions, namely, control by partial coherence.

We demonstrated active carrier-envelope-phase (CEP)-shift by utilizing a 4f-pulse-shaper in a CEP-stabilized chirped-pulse-amplification system. A combination of a pulse-shaper and CEP-stabilized pulses enables us to design electric fields, both the pulse envelope and the carrier-envelope relation.

A novel all-optical, all-fibre pulse retiming system is experimentally demonstrated. Our technique relies on converting the timing jitter into frequency shift using XPM switching of the data signal with parabolic pulses shaped using a SSFBG. (2 pages)

Tailored femtosecond laser pulses from a computer-controlled pulse shaper were used to optimize the branching ratios of different organometallic photodissociation reaction channels. The optimization procedure is based on the feedback from reaction product quantities in a learning evolutionary algorithm that iteratively improves the phase of the applied femtosecond laser pulse. In the case of CpFe(CO) 2 Cl, it is shown that two different bond-cleaving reactions can be selected, resulting in chemically different products. At least in this case, the method works automatically and finds optimal solutions without previous knowledge of the molecular system and the experimental environment.

The quality of tracks obtained from a streamer chamber is studied through the measurement of the streamer brightness. The stability of streamer tracks depends on the value of the high voltage applied and its shape. By using a single conical-type spark gap as the pulse shaper, stable brightness of the streamer tracks is attained. The data on the streamer brightness are compared with the result by Bulos et al. and it is found that the brightness is more strongly affected by field parameters than in their result.