WO1996024180A1 - Appareil creant un retard de phase dans une impulsion et son procede d'utilisation - Google Patents

Appareil creant un retard de phase dans une impulsion et son procede d'utilisation Download PDF

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Publication number
WO1996024180A1
WO1996024180A1 PCT/US1996/001018 US9601018W WO9624180A1 WO 1996024180 A1 WO1996024180 A1 WO 1996024180A1 US 9601018 W US9601018 W US 9601018W WO 9624180 A1 WO9624180 A1 WO 9624180A1
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Prior art keywords
grating
pulse
sod
tod
positive
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PCT/US1996/001018
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English (en)
Inventor
Jeffrey A. Squier
Steven J. Kane
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The Regents Of The University Of Michigan
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Application filed by The Regents Of The University Of Michigan filed Critical The Regents Of The University Of Michigan
Priority to AU49659/96A priority Critical patent/AU4965996A/en
Publication of WO1996024180A1 publication Critical patent/WO1996024180A1/fr
Priority to CA002228370A priority patent/CA2228370C/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0057—Temporal shaping, e.g. pulse compression, frequency chirping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/0811—Construction or shape of optical resonators or components thereof comprising three or more reflectors incorporating a dispersive element, e.g. a prism for wavelength selection
    • H01S3/0812—Construction or shape of optical resonators or components thereof comprising three or more reflectors incorporating a dispersive element, e.g. a prism for wavelength selection using a diffraction grating
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1106—Mode locking

Definitions

  • This invention relates generally to an apparatus and a method for providing a phase shift in an optical pulse.
  • This invention may be used in a variety of applications pertaining to optical pulses and more specifically to high speed optical devices and techniques, including lasers.
  • optical materials including crystals, glasses, liquids, and other dielectrics, possess the property of dispersion.
  • SOD second-order dispersion
  • TOD positive third-order dispersion
  • Dispersion can be most simply described as a frequency dependent transit time through the medium. All optical pulses are composed of multiple frequencies and, therefore, in the presence of dispersion, the different frequency components of the pulse will arrive at their destination at different times.
  • This frequency dependent transit time will degrade the shape of an output pulse, providing second-order dispersion (SOD), wherein the transit time varies linearly with frequency, or (SOD), will cause a broadening of the pulse; and third-order dispersion (TOD) where the transit time varies with the square of the frequency, or (TOD), will result in asymmetric distortion of the pulse shape.
  • SOD second-order dispersion
  • TOD third-order dispersion
  • a prism pair is known to compensate for small amounts of SOD and TOD.
  • Prism pairs are used in three configurations. They are: (1) standard configuration where the prism pair provides negative SOD and negative TOD; (2) a first non-standard configuration where the prism pair provides zero SOD and negative TOD; and (3) a second non-standard configuration where the prism pair provides positive SOD, negative TOD. It is clear that prisms can be used to provide compensation of material dispersion in all three regimes, namely, normal, zero dispersion, and the anomalous regime. Optical materials used in many laser applications most typically and almost always provide positive SOD and positive TOD during generation, stretching, and amplification of the pulse.
  • prisms disposed in a standard configuration and providing negative SOD and negative TOD can compensate for such distortion. Accordingly, prisms can be used to provide compensation of material dispersion in all three regimes and importantly in the normal regime. However, the prisms can only be used to compensate for very small amounts of dispersion, as the physical dimensions of the prism sequence are much larger than the lengths of the material they are compensating. For example, a one centimeter piece of sapphire used in a laser system, which imparts SOD and TOD to a pulse, can be compensated by a pair prisms which are about fifty centimeters apart (see Figure 1).
  • the prism separation scales linearly with the length of the dispersive material; therefore, to compensate the SOD and the TOD of a pulse which has travelled through a short optical fiber, for example, one hundred meters, the prism space needed to compensate SOD and TOD would be more than two miles.
  • prisms are not practical to compensate for large amounts of SOD and TOD, and even for laser sources which only have one centimeter of material, a fifty centimeter prism sequence is not a very compact way to compensate for dispersion.
  • grating pairs which can provide very large amounts of dispersion and compensation.
  • Such grating pairs provide compensation in three modes, none of which can compensate for both SOD and TOD in the normal regime, which is of greatest interest, and in the zero dispersion regime.
  • Treacy in the IEEE Journal of Quantum Electronics, Volume QE-5, No. 9, September 1969 describes a grating pair which provides negative SOD and positive TOD. Therefore, Treacy is not able to provide negative SOD and negative TOD compensation.
  • Tournois describes a grating pair which provides negative SOD but zero TOD.
  • Tournois cannot provide compensation for normal regime positive SOD and positive TOD of optical materials.
  • Martinez in a paper published in IEEE Journal of Quantum Electronics, Volume QE-23, No. 1, January 1987 describes a grating pair which provides positive SOD and negative TOD.
  • Martinez cannot provide negative SOD and negative TOD to compensate for the positive SOD and positive TOD generated by most, if not all, optical materials used in generating optical pulses.
  • Another object is to provide an apparatus for the production of one or more pulses which comprises one or more of the grating elements of the invention.
  • the invention provides an apparatus for imparting a phase shift, typically a phase delay, in one or more pulses.
  • the apparatus comprises a pair of optical diffraction grating elements.
  • Each one of the grating elements comprises a grating in light coupling arrangement with a dielectric body to accept a pulse which is transmitted therethrough.
  • the grating has a constant line spacing (d).
  • the dielectric body has a side through which the pulse traverses and this side through which the pulse traverses is at an angle ⁇ (alpha) with respect to the grating.
  • the angle ⁇ (alpha) defines or identifies the path of the pulse transmitted through the dielectric body corresponding to an incident angle ⁇ (theta) between the path of the pulse and a plane normal to the grating.
  • Grating elements so constructed and arranged provide negative second-order dispersion (SOD) and negative third- order dispersion (TOD) so as to compensate for any positive SOD and any positive TOD initially present in the pulse.
  • the grating is in the form of a pattern on the surface of the dielectric body.
  • the grating is a patterned surface on a substrate which is affixed to the dielectric body in light coupling arrangement or light transmission arrangement.
  • the attachment is by a dielectric glue, cement, or the like.
  • the grating is written, etched, or engraved on a surface of the dielectric body.
  • the grating may be in the form of a pattern formed by holographic means.
  • the apparatus for imparting a phase shift is used as a compressor as a part of a larger system for producing laser pulses.
  • a compressor comprises means to generate the optical pulse, means to stretch the pulse, and means to amplify the pulse.
  • the compressor comprises the grating elements, as described immediately above, for providing negative SOD and negative TOD so as to compensate for any positive SOD and any positive TOD induced by the generating, stretching, and amplifying of the pulse preceding its entry into the compressor.
  • the apparatus for imparting a phase shift may be used in combination with an optical fiber stretcher, direct injection, or intralaser pulse formation.
  • the apparatus for imparting a phase shift may be used as a compressor where the means to generate, stretch, and amplify a pulse comprises an oscillator, fiber optic stretcher, and regenerative amplifier.
  • an apparatus for producing one or more pulses which comprises means to stretch the pulse in time comprising a pair of optical diffraction grating elements where each one of the grating elements has a grating in light coupling arrangement with a dielectric body to accept the pulse.
  • the grating elements are spaced apart with optical imaging system disposed between the grating elements that optically displaces the apparent placement of the grating elements with respect to one another, thereby providing positive SOD and positive TOD in the pulse.
  • a compressor which comprises a pair of optical diffraction grating elements where each one of the grating elements comprises a grating in light coupling arrangement with the dielectric body to accept the stretched pulse and to provide negative SOD and negative TOD so as to compensate for the positive SOD and positive TOD induced by the stretching.
  • the imaging system of the stretcher is negative magnification
  • the gratings of the stretcher are arranged anti-parallel.
  • the imaging system is positive magnification and the gratings of the stretcher are arranged in parallel configuration with respect to one another.
  • an apparatus for stretching and compressing one or more pulses comprises an optical diffraction grating element comprising a grating in light coupling arrangement with the dielectric body; and a mirror spaced from the grating element. A lens is disposed between the mirror and the grating element. A corner or dihedral reflector is also spaced from the grating element.
  • the grating element, lens, and mirror are all arranged to define a first beam path which traverses through the grating element, then through the lens, and then through the mirror.
  • the grating element and dihedral reflector are arranged with respect to one another so as to define a second beam path which traverses through the grating element and to the reflector.
  • the dielectric body has a side through which the pulse traverses and this side is at an angle ⁇ (alpha) with respect to the grating where ⁇ (alpha) defines the path of the pulse in the dielectric body to provide an incident angle ⁇ (theta) between the path and a plane normal to the grating to provide positive SOD and positive TOD in the stretcher and negative SOD and negative TOD in the compressor.
  • the grating element, lens, and mirror which define the first beam path provide positive SOD and positive TOD as they function as the stretcher.
  • the grating element and corner reflector in this configuration, provide negative SOD and negative TOD to compensate for the positive SOD and positive TOD induced in the aforesaid stretcher.
  • the apparatus for imparting a phase shift which comprises one or more of the above described grating elements having an angle ⁇ (alpha) which identifies the path of the pulse in the dielectric body corresponding to an incident angle ⁇ (theta) between the beam path and a plane normal to the grating, is particularly useful when incorporated into a chirped-pulse amplification laser system. It very effectively provides negative SOD and positive TOD so as to compensate for any positive SOD and any positive TOD present in the pulse as a result of other components of the CPA system.
  • ⁇ (xi) which is defined as the third-order dispersion (TOD) divided by the absolute value of the second-order dispersion (SOD).
  • TOD third-order dispersion
  • SOD second-order dispersion
  • ⁇ (xi) there are several parameters which may be varied, including, the grating group spacing d, the index of refraction of the dielectric n, and the angle of incidents ⁇ i (theta).
  • the angle of incidents ⁇ i (theta) is in turn dependent on the angle ⁇ (alpha) between the grating or the surface which carries the grating pattern, and the side of the dielectric body through which the light is transmitted.
  • optical diffraction grating elements when used as a compressor and/or stretcher in laser systems provide the advantage of ease of set-up and alignability.
  • the optical diffraction grating elements of the invention provide essentially perfect compression of a pulse close to, and within a few percent of, the transform limit.
  • Figure 1 is a schematic of a standard titanium sapphire mode-lock laser system in which compensating prisms occupy a significant portion of the total area occupied by the system.
  • Figure 2 is an illustration of an optical diffraction grating element, dispersive device, having a transmission grating.
  • Figure 3 is an illustration of an optical diffraction grating element, dispersive device, having a reflection grating.
  • Figure 4 illustrates a pair of optical diffraction grating elements where each of the elements is a transmission grating element as described with respect to Figure 2 and having all angles determined by the orientation of the center wavelength with respect to the grating normal.
  • Figure 5 illustrates a pair of optical diffraction grating elements where each of the elements is a reflection grating element as described with respect to Figure 3 and having an incident angle measured with respect to the grating normal and a diffraction angle subtended by the central wavelength and the normal of the dielectric's face from which the beam is emitted.
  • Figures 6 and 7 are schematics of chirped pulse amplification (CPA) laser systems for providing a laser beam
  • the stretcher of the system is a fiber stretcher and the compression means comprises a pair of transmission gratings ( Figure 6) or a pair of reflection gratings ( Figure 7), respectively.
  • CPA chirped pulse amplification
  • Figures 8 and 9 are schematics of direct injection type CPA laser systems with compression means comprising transmission grating elements ( Figure 8) and reflection grating elements ( Figure 9), respectively.
  • Figure 10 is a schematic of CPA laser system having stretcher means comprising a pair of transmission grating elements with optical imaging device and compression means comprising a pair of transmission grating elements.
  • Figure 11 is similar to Figure 10 except that the stretching means comprises reflection grating elements and the compression means comprises reflection grating elements.
  • Figure 12 illustrates a pair of grating elements disposed in a parallel configuration.
  • Figure 13 illustrates a pair of grating elements disposed in an anti-parallel configuration.
  • Figures 12 (A) and 13 (A), respectively, show negative magnification and positive magnification optical imaging systems for use with grating elements of respective Figures 12 and 13.
  • Figure 12 (A) the angle of a ray is not preserved in a negative magnification system; a ray exiting this system is anti-parallel to the ray which entered the system.
  • Figure 13 (A) the angle of a ray is preserved in a positive magnification system; a ray exiting this system is parallel to the ray which entered the system.
  • Figure 14 is a 3-dimensional illustration of a unitary grating stretcher and compressor. A portion of the grating element illustrated as the top half is the stretching means and the bottom half is the compressor means. The single grating element is used to provide the same incident angle for both the stretching and compressing.
  • Figure 15 is a top view according to Figure 14.
  • Figure 16 shows the results of modeling a 100 femtosecond pulse which was stretched to 250 picoseconds in a fiber and compressed with three different devices: devices (a) and (b) are conventional compressors and device
  • Figure 17 shows the auto-correlation of a 60 femtosecond pulse stretched to 60 picoseconds in a fiber and compressed according to the apparatus and method of the invention.
  • Figure 18 is a schematic of a modified titanium sapphire mode-lock laser modified as compared to Figure 1.
  • the compression means comprises grating elements as shown in Figure 18 which are a fraction of the size of a conventional prism sequence previously shown in Figure 1.
  • Figure 19 shows the monolithic device comprised of a pair of transmission grating elements (10, 12) and a dielectric body (200).
  • Figure 20 shows the monolithic device comprised of a pair of reflective grating elements (10, 14) and a dielectric (200).
  • FIGS 2 and 3 each show an apparatus for imparting phase shift in one or more pulses of a pulse beam (5).
  • the apparatus comprises at least one optical diffraction grating element (10).
  • Each one of the grating elements comprises a grating (15) having an essentially constant line spacing (d) and a dielectric body (20) in light coupling arrangement with the grating (15).
  • the dielectric body has a side (25) through which the pulse traverses.
  • the side (25) is at an angle ⁇ (alpha) with respect to the grating (15).
  • the angle ⁇ (alpha) defines a path (30) of the pulse in the dielectric body (20) corresponding to an incident angle ⁇ i (theta incident) between the path (30) and a plane (35) normal to the grating (15).
  • the incident angle ⁇ i (theta incident) and the grating line spacing (d) cooperate to provide negative second-order dispersion and negative third-order dispersion so as to compensate for any positive second-order dispersion and any positive third-order dispersion initially present in the pulsed beam (5).
  • the grating element (10) is characterized by an angle of diffraction ( ⁇ d ) between a path (40) of the pulse emitted from a side (45) of the grating element (10) and a plane (50) normal to the side (45) of the grating element (10) from which the pulse is emitted.
  • ⁇ d angle of diffraction
  • Figure 2 shows a grating element (10) which is a transmission grating element (12) having a grating (15) which is transmission grating (16).
  • Figure 3 shows a grating element (10) which is a reflection grating element (14) having a grating (15) which is a reflection grating (18).
  • the pair of transmission grating elements (12) shown in Figure 4 is each characterized by an angle of diffraction ⁇ d between a path of the pulse emitted from the grating element (12) and the plane (35) normal to the grating (15, 16) from which the pulse is emitted.
  • ⁇ d is related to ⁇ 4 as described in connection with Figure 2.
  • the plane (35) normal to the transmission grating (15, 16) defines one of the legs by which ⁇ i is subtended, plane (35) is the same plane as plane (50) that defines one of the legs by which ⁇ d is subtended; that is plane (35) and plane (50) are the same.
  • all angles are determined by the orientation of the center wavelength (7) of the beam (5) with respect to the grating normal (35, 50) or the plane normal (35, 50) to the grating (15, 16).
  • the pair of reflection grating elements (14) as shown in Figure 5 are each characterized by an angle of diffraction ⁇ d between a path of the pulse emitted from a side (45) of the dielectric (20) opposite the grating (15, 18) and a plane (50) normal to the side (45) from which the pulse is emitted as shown in Figures 3 and 5.
  • ⁇ d is related to ⁇ d as identified in connection with Figure 2 and generally applicable to each of the optical diffraction grating elements (10) of the invention.
  • plane (35) is normal to the grating (15, 18)
  • plane (50) is normal to a side (45) of the dielectric (20) opposite the grating (15, 18).
  • the incident angle ⁇ i is defined with respect to the grating normal (35), and the diffracted angle ⁇ d is the angle subtended by a central wavelength (7) of the beam (5) and a normal (50) of the dielectric's face (45) from which the beam (7) is emitted.
  • the dielectric (20) be in the shape of a prism or a parallelopiped, but this is not necessary.
  • the only requirement is that any side of the dielectric body (20) through which the beam traverses is essentially flat. That is, any surface forming a face of the dielectric through which the beam is transmitted should be flat so that in the case of the transmission mode two faces are required to be flat as shown in Figures 2 and 4 because light is transmitted through sides (25) and (45).
  • each of the grating elements (14) have three flat surfaces since there are three different surfaces from which light may be reflected or transmitted. That is, one surface having the grating from which light is reflected, and two other surfaces through which light may be transmitted.
  • each of the optical diffraction grating elements (10) be constructed and arranged so that ⁇ i (theta incident) is related to ⁇ (alpha) according to the expression: ⁇ i - ⁇ c ⁇ ⁇ ⁇ ⁇ i + ⁇ c , where ⁇ c equals arcsin 1/n and n is the index of refraction of the dielectric (20). It is most preferred that ⁇ (alpha) is about equal to ⁇ i (theta incident).
  • the gratings (15) may be provided in a variety of forms so long as the grating line spacing (d) and line density (1/d) are as defined above.
  • the gratings may be in the form of a pattern on the surface of the dielectric body (20), or engraved, written, or inscribed on a surface of the dielectric body (20). In one embodiment, the gratings are in the form of grooves. In another embodiment, the grating (15) is formed as a holographic pattern on the surface of the dielectric body (20). The grating (15) may be provided on a substrate which is then placed in light coupling arrangement with the dielectric body (20). There are several dielectric adhesives or cement which permit the grating element (10) to be comprised of two separate pieces, the dielectric body (20) and the grating (15) carried on the substrate. In its most preferred form, however, the grating (15) is in the form of a pattern in or on the surface of the dielectric body (20) so that the grating element (10) is essentially a single unitary body.
  • each of the elements in the pair be either reflection gratings or transmission gratings; and that an optional retro-reflector (52) be used.
  • an optional retro-reflector (52) be used.
  • a grating element (10) of the invention whether reflection (12) or transmission (14) in combination with another type of grating element. Accordingly, each of the embodiments of the grating element (10) as generally described in Figures 2 and 3 are useful either alone or in combination with a variety of other types of grating elements.
  • the grating elements of Figures 2 through 5 are adaptable for a variety of uses, including but not limited to a combination in which one or more of the grating elements is used with an optical fiber; a combination in which one or more of the grating elements is used in a direct injection system for forming an optical pulse; a combination in which one or more of the grating elements, as defined herein, are used as a stretcher portion and as a compressor portion of an overall laser system; and a combination in which one or more of the grating elements, as defined herein, is used in combination with a laser medium in an intra-laser configuration.
  • a chirped pulse amplification (CPA) laser system The use of one or more of the grating elements, as defined herein, in a chirped pulse amplification (CPA) laser system will now be described.
  • the specifics of the chirped pulse amplification laser system for providing a pulsed beam are known and will not be repeated here as they are described in U.S. Patent Number 5,235,606 which is incorporated herein by reference in its entirety.
  • Such systems can be roughly divided into four categories. The first includes the high energy, low repetition system such as ND glass lasers with outputs of several joules but they may fire at less than 1 shot per minute.
  • a second category are lasers that have an output of approximately one joule and repetition rates from 1 to 20 hertz.
  • the third group consists of millijoule level lasers that operate at rates ranging from 1 to 10 kilohertz.
  • a fourth group of lasers operates at 250 to 350 kilohertz and produces 1 to 2 microjoules per pulse.
  • U.S. Patent No. 5,235,606 several solid-state amplifying materials are identified and the invention is illustrated using Alexandrite.
  • the examples which are described hereinbelow and are shown in prior art Figure 1 use Ti: sapphire. This is merely illustrative and other laser media such as glass, LiSAF,
  • Alexandrite, dyes, LiCAF, and the like may be used.
  • a basic scheme for CPA first a chirped pulse is generated.
  • the pulse from the oscillator is sufficiently short so that further pulse compression is not necessary.
  • it is stretched by a grating pair arranged to provide positive group velocity dispersion.
  • the amount the pulses are stretched depends on the amount of amplification. Below a millijoule, tens of picoseconds are usually sufficient.
  • a first stage of amplification typically takes place in either a regenerative or a multi-pass amplifier. In one configuration, this consists of an optical resonator that contains the gain media, a Pockels cell, and a polarizer. After the regenerative amplification stage, the pulse can either be recompressed or further amplified.
  • the means of compression preferably consist of a grating or grating pair as defined by the invention, and as shown in Figures 6 and 7 , providing negative second-order dispersion and negative third-order dispersion in order to compensate for any positive second-order dispersion and any positive third-order dispersion which may have been present in the pulsed laser beam prior to compression.
  • Figure 6 shows a schematic of a preferred chirped pulse amplification design which incorporates a pair of transmission grating elements (12) as a compressor (55) and an optical fiber (60) as the stretcher.
  • the system also includes an oscillator (66) and an amplifier (67) as more particularly described in U.S. Patent No. 5,235,606.
  • the oscillator (66), fiber stretcher (60), and amplifier (67) provide the means to generate, stretch, and amplify an optical pulse and the transmission grating compressor (55) provides the means to induce negative second-order dispersion and negative third-order dispersion so as to compensate for any positive second- order dispersion and any positive third-order dispersion induced by the generating, stretching, and/or amplifying of the pulse.
  • Figure 7 is similar to Figure 6 except that the compression means is a reflection grating compressor (65), utilizing a pair of reflection grating elements (14).
  • the oscillator produces a beam of laser pulses having a frequency of 100 femtoseconds and 1 nanojoule.
  • the pulse is stretched to 250 picoseconds with 0.5 Nanojoules and the amplifier produces a pulse at
  • the condition of the pulse is typically 100 femtoseconds and
  • Figure 8 illustrates a schematic of a direct injection CPA or chirped pulse amplification laser system which is of a direct injection design and comprises a laser medium (68) and means for dispersion compensation.
  • the system comprises an oscillator (66), an amplifying medium (68), a dispersive medium (70), and a pair of transmission grating elements (12) forming a transmission compressor (55).
  • Figure 9 is the same as Figure 8 except that the transmission grating compressor (55) has been replaced by reflection grating compressor (65) in the direct injection CPA system.
  • the short pulse is directly injected into the amplifier and is stretched during each round trip by a dispersive intracavity element.
  • the condition of the pulse in such a system is illustrated by the following values: oscillator produces a 50 femtosecond pulse at 1 nanojoule; regenerative amplifier after 20 round trips produces a 40 picosecond pulse at 2 to 5 microjoules; and after compression by the optical diffraction grating elements of the invention the output pulse is at 50 femtoseconds and 1 to 5 microjoules.
  • an apparatus for producing a beam comprising one or more laser pulses comprises a pair of grating elements (10) prepared and arranged in accordance with the invention to function as a stretcher (80) and a second pair constructed and arranged to function as a compressor (85).
  • Figure 11 is the same as Figure 10 except that in Figure 11 the stretcher (82) and compressor (86) are reflection grating elements (14), whereas in Figure 10 the stretcher (80) and compressor (85) are transmission grating elements (12).
  • the means to stretch the pulse in time comprises a pair of optical diffraction grating elements (10), where each one of the grating elements (10) comprises a grating (15) in light couple arrangement with the dielectric body (20) to accept the pulse as described hereinabove.
  • the grating elements (10) are spaced apart with optical imaging system (90) disposed between the grating elements (10).
  • the optical imaging system (90) optically displaces the apparent placement of the grating elements (10) with respect to one another.
  • the optical imaging system (90) in combination with the grating elements (10) provides positive second- order dispersion and positive third-order dispersion in the pulse.
  • the system further comprises grating compressor (85) comprising a pair of optical diffraction grating elements (10) constructed and arranged as described hereinabove.
  • the imaging system (90) is negative magnification (90A of Figure 12 (A)) when the grating elements (10) of the stretcher (80) are arranged anti- parallel as shown in Figure 12.
  • the imaging system (90) is positive magnification (90B of Figure 13 (A)) when the grating elements (10) of the stretcher (80) are arranged in parallel configuration as shown in Figure 13.
  • Figure 10 shows the stretcher (80) and compressor (85) being formed of transmission grating elements (12).
  • the grating pattern surface (15) of the grating elements (10) are arranged such that the surfaces (15) are parallel to one another.
  • the pattern surfaces (15) are not parallel to one another.
  • the lenses (105a, 105b) of Figure 12 (A) provide negative magnification system (90A) and the lenses (105c, 105d, 105e) of Figure 13 (A) provide positive magnification system (90B).
  • an apparatus for stretching and compressing one or more pulses and comprises an optical diffraction grating element (10) in light coupling arrangement with a dielectric body (20).
  • a mirror (100) is spaced from the grating element (10).
  • a lens (105) is between the mirror (100) and the grating element (10).
  • the grating element (10), lens (105), and mirror (100) are arranged to define a first beam path (110) with a first central wavelength (112) which traverses through the grating element (10), through the lens (105), and to the mirror (100).
  • the grating element (10) and dihedral reflector (120) are arranged to define a second beam path (130) with a second central wavelength (132) which traverses through the grating element (10) and to the corner reflector (120).
  • the dielectric body (20) has a side (a) through which the pulse traverses. Both the first beam path (110) and the second beam path (130) traverse through side (a).
  • Side (a) is at an angle ⁇ (alpha) so that ⁇ (alpha) defines the path of the pulse in the dielectric body (20) corresponding to an incident angle ⁇ i between the beam path (110, 112) and a plane normal to the grating, which in cooperation with lens (105) provides positive second-order dispersion and positive third-order dispersion as the beam traverses in the first beam path (110).
  • Lens (105) and mirror (100) comprise a negative magnification optical imaging system. Negative second-order dispersion and negative third-order dispersion is provided as the beam travels in the second beam path (130, 132), as shown in Figure 14.
  • a single grating stretcher and compressor (200) provides, respectively, positive second-order dispersion, positive third-order dispersion; and negative second-order dispersion, negative third-order dispersion.
  • One portion is the stretcher and the other portion is the compressor.
  • the stretcher is illustrated as the top half and the compressor is illustrated as the bottom half.
  • the same grating is used at the same incident angle ⁇ i for the stretcher and the compressor.
  • a quantity is defined to conveniently characterize a stretcher (either a grating pair or dispersive material, like a fiber) or compressor:
  • n(w) the index of the phase with respect to w to obtain the quadratic and cubic coefficients ⁇ 2 and ⁇ 3 , and therefore, determine the parameter ⁇ .
  • n p index of the dielectric
  • ⁇ is the wavelength of light
  • m is the order of diffraction
  • a glass which is easily obtainable BK-10 glass from Schott.
  • the value of m is equal to one.
  • an incident angle on the grating 74 degrees, for example.
  • any two of the grating parameters can be specified as given, and the third parameter can be obtained by solving equation (4).
  • FIG. 16 shows the results of modeling a 100 femtosecond pulse which was stretched to 250 picoseconds in a fiber and compressed with three different devices: (a) conventional grating that provides positive TOD, opposite to that desired; (b) conventional grating that cannot provide any third-order dispersion, of no practical use to provide the desired dispersion; and (c) a pair of optical diffraction grating elements prepared according to the specification of the invention which provides complete compensation of dispersion as per Figure 6. It can be seen from Figure 16 that the optical diffraction grating elements of the invention provide near perfect compression and compensation while the others leave huge wings on the pulse.
  • Figure 17 shows the auto-correlation of a 60 femtosecond pulse stretched to 60 picoseconds in a fiber and compressed according to the apparatus and method of the invention demonstrating the utility of the invention in short pulse microjoule lasers.
  • a standard grating pair can never achieve the large negative values of ⁇ " necessary for operation in the negative-cubic-phase regime; however, in the new compressor of the invention, the index change across the grating reverses the sign of ⁇ ", and allows for the rate of change to be of sufficient magnitude such that the cubic phase can flip sign.
  • the Figure 1 mode-locked Ti:Al a O 3 and rare-earth-doped fiber lasers now utilize prisms to cancel the second- and third-order dispersion of the gain medium.
  • Prism sequences are not very compact; the prisms in Ti:Al 2 O 3 oscillators is typically 50 centimeters apart ( Figure 1), and the six- prism sequence in some fiber lasers can be as long as 1.5 meters.
  • the invention provides compact femtosecond sources, by providing optical diffraction grating elements (10) as in Figure 18.
  • Such intracavity grating elements provide the same cubic-phase compensation as a prism sequence, but require separation of only millimeters. (Figure 18.)
  • This scheme can be used in any laser cavity requiring SOD and TOD compensation. There is less than one centimeter distance between gratings (10), with end mirror pushed against or coated onto grating glass.
  • this device In order to operate in the negative- ⁇ 3 regime, this device relies on a large index change across the grating; in the CPA compressor, this index difference is about 0.7 (glass to air).
  • Figure 19 shows the monolithic device comprised of a pair of transmission grating elements (10, 12) and a dielectric (200).
  • Figure 20 shows the monolithic device comprised of a pair of reflection grating elements (10, 14) and a dielectric (200). The equations governing this device would be:
  • n p /n s Operation in the negative- ⁇ 3 regime is therefore possible if n p /n s is sufficiently large.
  • a compressor with high-index flint glass (n P ⁇ 1.9) on the outside of the gratings and a low-index material like magnesium fluoride (n s ⁇ 1.37) between the grating elements (10) will behave like an air-spaced compressor with an index n p of 1.4.
  • This one-piece (unitary) device would be very easy to implement, and would be useful for compensating fixed amounts of material dispersion.
  • high-index materials generally contribute large amounts of positive dispersion, and the dispersion of the high-index prisms in this device can no longer be neglected.
  • the compressor can be self-compensating, cancelling not only the dispersion of the laser medium but also the dispersion of its own prisms.
  • the invention provides novel optical diffraction grating elements and more specifically transmission and reflection optical diffraction grating elements with third-order dispersion opposite to that of a traditional grating pair.
  • the invention also provides apparatus and method for easily alignable and easily tunable stretchers and compressors utilizing the novel grating elements.
  • the angle ⁇ i in the stretcher and compressor are preferably identical; and the stretcher and compressor are preferably identical. Further, the compressor angle is independent of the amplifier length. With proper choice of index of refraction, grating spacing, and ⁇ i , it is possible to configure a stretcher or compressor such that third-order dispersion and second-order dispersion are of the same sign.
  • the stretcher utilizes the exact same grating elements as the compressor but incorporates a one to one telescope.
  • the grating elements may be made as a single, unitary structure having the gratings patterned or written onto the surface of a dielectric or the gratings may be written onto a flat substrate which is then attached by optical cement to a dielectric.
  • a grating element in accordance with the invention where the same element is used for both the stretcher and the compressor where suitable reflector mirror lenses define a beam path based on the design of the grating element which satisfies the requirement of positive SOD, positive TOD in the stretcher and negative SOD, negative TOD in the compressor.
  • the potential for commercial application of these optical diffraction grating elements is considerable, including the elimination of conventional stretchers and compressors in laser systems which would result in greater ease of use and reduce the size of these systems.
  • the optical diffraction grating elements when used as a compressor and/or stretcher in laser systems provide the advantage of ease of set-up and alignability.
  • the optical diffraction grating elements of the invention provide essentially perfect compression of a pulse close to, and within a few percent of, the transform limit.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

L'invention porte sur un procédé et un appareil conférant un décalage de phase à une ou plusieurs impulsions. L'appareil comprend au moins un porte-grille de diffraction optique dont chacun est pourvu d'une grille présentant un interligne (d) constant et un corps diélectrique couplé optiquement à la grille, le corps diélectrique présentant un côté traversé par les impulsions. Ledit côté forme avec la grille un angle alpha (α) déterminant la trajectoire de l'impulsion à l'intérieur du corps diélectrique correspondant à un angle d'incidence Υi (théta incident) formé par ladite trajectoire et un plan normal à la grille. L'angle υi et l'interligne de la grille (d) concourent à la production d'une dispersion négative de second ordre (SOD) et une dispersion négative de troisième ordre (TOD) destinées à compenser toute dispersion positive de deuxième ou de troisième ordre initialement présente dans l'impulsion.
PCT/US1996/001018 1995-02-01 1996-01-23 Appareil creant un retard de phase dans une impulsion et son procede d'utilisation WO1996024180A1 (fr)

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AU49659/96A AU4965996A (en) 1995-02-01 1996-01-23 Apparatus for providing a phase shift in a pulse and method of use thereof
CA002228370A CA2228370C (fr) 1995-08-31 1996-08-29 Derives de piperazino antagonistes de la neurokinine

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR3137221A1 (fr) * 2022-06-27 2023-12-29 Amplitude Système et procédé de compression d’impulsions lumineuses

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FR2652421A1 (fr) * 1989-09-26 1991-03-29 Max Planck Gesellschaft Compresseur optique d'impulsions.
US5329398A (en) * 1992-11-05 1994-07-12 Novatec Laser Systems, Inc. Single grating laser pulse stretcher and compressor
EP0626740A1 (fr) * 1993-05-18 1994-11-30 Thomson-Csf Ligne à retard optique dispersive et son utilisation pour la compression/extension d'impulsions laser

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US3549239A (en) * 1968-11-19 1970-12-22 United Aircraft Corp Optical signal processor
US3696310A (en) * 1970-10-01 1972-10-03 Bell Telephone Labor Inc Mode-locking in semiconductor lasers
FR2652421A1 (fr) * 1989-09-26 1991-03-29 Max Planck Gesellschaft Compresseur optique d'impulsions.
US5329398A (en) * 1992-11-05 1994-07-12 Novatec Laser Systems, Inc. Single grating laser pulse stretcher and compressor
EP0626740A1 (fr) * 1993-05-18 1994-11-30 Thomson-Csf Ligne à retard optique dispersive et son utilisation pour la compression/extension d'impulsions laser

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Title
H.KUBOTA ET AL.: "Compensation of nonlinear chirp generated by self-steepening using third order dispersion of a grating pair", OPTICS COMMUNICATIONS, vol. 66, no. 2,3, 15 April 1988 (1988-04-15), AMSTERDAM NL, pages 79 - 82, XP002007266 *
KANE S ET AL: "GRATING COMPENSATION OF THIRD-ORDER MATERIAL DISPERSION IN THE NORMAL DISPERSION REGIME: SUB-100-FS CHIRPED-PULSE AMPLIFICATION USING A FIBER STRETCHER AND GRATING-PAIR COMPRESSOR", IEEE JOURNAL OF QUANTUM ELECTRONICS, vol. 31, no. 11, 1 November 1995 (1995-11-01), pages 2052 - 2057, XP000541548 *
MIKLOS STERN ET AL: "GRATING COMPENSATION OF THIRD-ORDER FIBER DISPERSION", IEEE JOURNAL OF QUANTUM ELECTRONICS, vol. 28, no. 12, 1 December 1992 (1992-12-01), pages 2742 - 2748, XP000315276 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR3137221A1 (fr) * 2022-06-27 2023-12-29 Amplitude Système et procédé de compression d’impulsions lumineuses
WO2024003068A1 (fr) * 2022-06-27 2024-01-04 Amplitude Système et procédé de compression d'impulsions lumineuses

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