Patent number 8716904 is assigned to Universite de Limoges (Lomoges, FR).
The following quote was obtained by the news editors from the background information supplied by the inventors: "Such a generator is intended to be used in applications in which it is necessary to transmit high-power short (on the order of a nanosecond or above) electrical pulses (several kilovolts). It is also important that it be capable of being synchronized with other electrical or optical systems. The prior art comprises purely electronic pulse generators. These generators make it possible to produce high-power electrical pulses lasting between several picoseconds and several milliseconds. Nevertheless, these generators are not capable of being perfectly synchronized with one another and also do not enable the spectral content of the output pulse to be controlled.
"To obtain high-power short electrical pulses--typically on the order of the nanosecond or above--it is known to use optoelectronic switching generators, called frozen wave generators. These generators use various semiconductor substrates. A number of switching modes are known, including a so-called 'avalanche' mode and a so-called 'linear' mode.
"A generator using an avalanche switching system is described in the patent document U.S. Pat. No. 4,782,222. This generator includes a semiconductor substrate block, two conductive elements coupled to said block and separated by a determined distance, a high-voltage power supply arranged between the two conductive elements as well as means for illuminating said block at a given wavelength so that most of the light penetrates said block over a distance below the distance between said two conductive elements. Such a system makes it possible to perform very high-voltage switching while requiring little optical energy.
"The photoconductor systems operating in an avalanche mode nevertheless have a certain number of disadvantages, including a significant time jitter (on the order of several tens of picoseconds) for synchronizing short pulses--nanoseconds or sub-nanoseconds. This time jitter associated with optoelectronic switching limits the possibilities of perfectly controlling the time and therefore spectral profile of the electrical signal produced. This results in poor reproducibility of the short photogenerated pulses.
"A linear generator is described in the publication WO 2007/074229. This generator includes means for storing electrical charges, a high-voltage source capable of charging said charge storage means. It also includes two passive doped-silicon photoconductive elements operating in a linear mode forming photosensitive switches, the first being connected to the reference potential and to storage means, and the second being connected to the storage means and to an effective charge. It finally includes a first light source capable of delivering a light pulse to said first photoconductor, a second light source capable of delivering a light pulse to said second photoconductor, as well as means for synchronizing the transmission delay between the first and the second light source.
"Such a generator makes it possible to provide electrical pulses of peak-to-peak amplitude of several kilovolts for a sub-nanosecond duration of the bipolar signal. In addition, the time jitter is made very low--on the order of a picosecond--thereby making it possible to finely control the profile of the spectrum of the signal delivered. Finally, this generator enables high reproducibility of the source and has a very long lifetime.
"However, a linear optoelectronic generator has a number of disadvantages. In particular, the control of the spectral content of the pulse by adjusting the time delay between the two photosensitive switches does not allow for sufficient control of said content. Moreover, the means for adjusting the time delay between the two photoswitches integrates a delay line, thereby making the system bulky. Such a generator cannot be synchronized with other electrical or optical systems. Finally, the linear mode requires a large amount of optical energy and therefore the use of bulky laser sources. Thus, there is no solution in the prior art that would make it possible to obtain a low-profile electrical pulse generator capable of being synchronized with other electrical or optical systems, with high-power (several kilovolts), short (nanosecond and below) pulses and with controllable spectral content."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "The objective of the present invention is to overcome these technical problems, by enabling high-voltage frozen-wave electrical pulse generators--which can provide high-power short pulses--to control the spectral content of the pulses, while making it capable of being synchronous with other electrical or optical systems. The approach of the solution involves finding, on the high-voltage frozen-wave electrical pulse generators of the prior art, other means for controlling the spectral content of the pulse than the introduction of a time delay. This led to the control of this spectral content by adjusting the power difference necessary for the illumination of each of the two semiconductor components. This difference can in particular be adjustable with a light source generating a beam, means for splitting said beam into two beam fractions as well as means for controlling the distribution of the respective powers of said two fractions of said beam. This modification of the incident power also allows for better compactness of the generator. To this end, the invention relates to a high-voltage electrical pulse generator of the type mentioned above in which, in addition to the features already mentioned, the activation system includes means for generating a laser light beam and means for splitting said laser beam into two laser beam fractions, in which each laser beam fraction is directed respectively toward a photoconductive element of the generation system, and said splitting means are capable of controlling the distribution of the respective powers of said two laser beam fractions according to the orientation of the polarization of the laser beam.
"Such a generator, formed by the combination of generation and activation systems, makes it possible to solve the aforementioned technical problems, since the profile of the pulses generated can be controlled by the orientation of the polarization of the beam, which can be achieved with very high precision. This makes it possible, on the one hand, to benefit from a very low time jitter because of the high-voltage frozen-wave pulse generation system and, on the other hand, to be capable of controlling the spectral content of the pulses, as their spectral profile is adjustable. In addition, the laser beam enabling the pulses to be activated CaO be directed to other systems or generators so as to act as a reference for the synchronization of all of the systems.
"In a specific embodiment, the splitting means include rectilinear polarization phase delay means and means for rectilinear polarization by beam separation arranged so as to separate said laser beam into two laser beam fractions, in which each laser beam fraction is directed respectively toward a photoconductive element of the generation system, and the distribution of the respective powers of said two laser beam fractions is controlled by orienting said rectilinear polarization phase delay means. In this case, it is the orientation of the rectilinear polarization phase delay means that will make it possible to modify the orientation of the rectilinear polarization of the laser beam coming from the laser source. The means for rectilinear polarization by beam separation will then split the laser beam into two fractions directed toward the two photoswitches. The respective powers of these two fractions will therefore be functions of the orientation of the polarization of the laser beam at the output of the rectilinear polarization phase delay means. The pulse profile will be a function of said respective powers, which will thus make it possible to control said profile by orienting the polarization of said laser beam.
"In a preferred embodiment, the rectilinear polarization phase delay means are constituted by a half-wave plate of which the optical axis is perpendicular to the sighting axis of the laser beam. In a preferred embodiment, the means for rectilinear polarization by beam separation are constituted by a Wollaston-type polarizer. Advantageously, the pulse activation system also includes focusing means arranged in front of the means for rectilinear polarization by beam separation, so as to focus each laser beam fraction respectively on a photoconductive element of the generation system. The switching efficacy is thus improved.
"Advantageously, the laser beam generation means are of the microlaser type. The power supplied by this type of source is indeed sufficient, on the one hand, for activating the pulses with high precision and, on the other hand, for directing a sufficient proportion of the laser beam toward other optical and/or electrical systems. Such a generator thus has a lower profile.
"This invention also relates to an installation of multiple high-voltage pulse generators including N high-voltage pulse generators, in which N is greater than or equal to two, and each generator includes a high-voltage frozen-wave pulse generation system and a system for activating said pulses; said generation system includes a first and a second photoconductive element, characterized in that:
"said activation system of each generator includes means for splitting a laser beam into two laser beam fractions, in which each laser beam fraction is respectively directed toward a photoconductive element of the generation system, and said splitting means are capable of controlling the distribution of the respective powers of said two laser beam fractions according to the orientation of the polarization of the laser beam,
"said activation system of one of said N generators includes means for generating said laser beam,
"said activation system of at least N-1 generators includes delay means arranged so as to synchronize said generators with one another, and
"each generator includes separation means arranged so as to direct a portion of said laser beam transmitted by said generation means toward said splitting means of said generator.
"Such an installation makes it possible to obtain a plurality of mutually synchronous pulse generators. It makes it possible in particular to generate high-voltage, high-power, short electrical pulses, which pulses are synchronized and capable of being directed toward different targets or coupled with one another to produce the coherent sum of their power.
"This invention finally relates to electro-optical pump-probe equipment including a high-voltage pulse generator and a probe system, in which said generator includes a high-voltage frozen-wave pulse generation system and a system for activating said pulses, in which said generation system includes a first and a second photoconductive element, characterized in that:
"said activation system includes means for generating a light laser beam and means for splitting said laser beam into at least two laser beam fractions, in which each laser beam fraction is respectively directed toward a photoconductive element of the generation system, and said splitting means are capable of controlling the distribution of the respective powers of said at least two laser beam fractions according to the orientation of the polarization of the laser beam,
"said generator includes separation means arranged so as to direct a portion of said laser beam toward said generation system and another portion toward said probe system, and
"the equipment comprises at least one delay means, which delay means are arranged on the path of one of said portions of said laser beam so as to synchronize said generator and said probe system with one another.
"Such equipment has the advantage of dedicating a portion of the activation laser beam to a probe system, which can also be used for diagnostic or imaging applications. The generator--which acts as a pump system--and the probe system are thus synchronous. In addition, the absence of a time jitter between the optical pulse and the electrical photoswitched wave enables a real-time analysis of the impact thereof on biological elements. Finally, the management of the optical switching energy enables the spectrum of the electrical pulse to be modified according to the target to be analyzed.
"In an embodiment intended to perform both the test and the excitation of the target, the light beams from the generator and the probe system are directed toward the same target. It is thus possible to excite the target with the generator and, at the same time, to test this same target with the same laser beam, but of which the spectrum has been expanded. In an embodiment intended to change the excitation wavelength by generating a continuum, the probe system comprises broadband nonlinear conversion means. The continuum thus generated by the conversion means is synchronous with the generator and enables the target to be tested with wavelengths different from those of the initial laser beam.
"In an embodiment intended to show the result of the test of the target, the probe system comprises imaging means. In an embodiment intended to recognize given compounds on the target, the imaging means are of the CARS nonlinear type (Coherent Anti-Stokes Raman Spectroscopy). It is thus possible to cut and code the continuum generated by the nonlinear conversion means and to apply the continuum thus treated to a target. This type of imaging means enables complex--and therefore precise--signatures of a given compound to be generated by obtaining a spectrum in response to an excitation spectrum transmitted in the direction of the compound. This thus enables the recognition of a given compound by its spectrum in response to a determined excitation spectrum.
"In another embodiment, the imaging means are of the nonlinear second harmonic generation type. In another embodiment, the imaging means are of the nonlinear fluorescence type."
URL and more information on this patent, see: Couderc, Vincent; Vergne, Bertrand; Leveque, Philippe. Variable-Spectrum High-Power Electrical Pulse Generator, and Facility and Equipment Operating Such a Generator. U.S. Patent Number 8716904, filed
Keywords for this news article include: High Voltage, Semiconductor,
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