JP5354653B2 - Spectral phase compensation method and spectral phase compensation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compensate a spectrum phase for generating an ultrashort light pulse of high repetition frequency with an inexpensive and simple device. <P>SOLUTION: The phase compensation for a spectrum of wide-band light Lw is performed by a spectrum phase compensation device 20 having a pair of optical elements 21A and 21B made of positively dispersed media. The optical elements 21A and 21B are each sectioned in a wedge-like shape, are arranged with slopes 21A<SB>1</SB>and 21B<SB>1</SB>facing each other, and variable in distance between a light incident surface 21A<SB>2</SB>and a light emitting surface 21B<SB>2</SB>parallel to each other by movement of at least one optical element along a slope of the another optical element, and form a parallel flat plate portion 21 having an adjustable thickness t adjusted to a thickness at which a phase difference between adjacent spectra is an integral multiple of 2&pi;. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a spectral phase compensation method and a spectral phase compensation apparatus that perform spectral phase compensation for generating an ultrashort optical pulse having a high repetition frequency.

With the development of laser technology in recent years, it has become possible to easily use an ultrashort pulse laser having a pulse width of 100 femtoseconds ( ^10-15 seconds) or less, and the technological development in the terahertz region has rapidly advanced. Yes.

  Femtosecond light pulses can be used not only for non-destructive and non-invasive measurement of materials using nonlinear optical response, ultra-fine processing of glass, metal and semiconductors, cutting and manipulation of cells, but also using the coherence of light. Application to OCT (Optical Coherence Tomography) that images the inside of an object, a light source of a multiphoton microscope, a terahertz wave generator with a wavelength of 30 μm to 3 nm, which becomes an electromagnetic wave for inspection instead of X-rays, and the like is expected.

  The generation of femtosecond light pulses is a technique for controlling the relative phase between spectral components of an optical pulse having a wide time width and compressing the time width to the extent of the Fourier transform limit. Since the spread of the optical pulse on the time axis is caused by the relative phase relationship between the spectral components of the optical pulse, pulse compression is performed by compensating the relative phase with respect to the frequency, that is, chirping. Linear chirp is also called second-order dispersion because it occurs when the light propagation constant has a constant group velocity dispersion, that is, when it has a square dependence on frequency.

  There is an increasing demand for further narrowing the time width of femtosecond light pulses, but if the time width of the light pulse is narrowed, the frequency spectrum width is correspondingly expanded, so that chirping is applied between all components of the expanded frequency spectrum. Therefore, it is necessary to compensate for the chirp over a wider frequency range than before.

  Here, the frequency chirp is a phenomenon in which the instantaneous frequency of an optical pulse changes with time. A case where it increases linearly with time is called a positive chirp, and a case where it decreases linearly is called a negative chirp.

  As shown in FIG. 11, a conventional general method for generating an ultrashort optical pulse includes a coherent and broad spectrum of an optical pulse (wideband light) Lw generated by a broadband light source and a phase of the spectrum for each spectral component. A method of generating an ultrashort optical pulse Lx by compensating and multiplexing is widely known as a general method of generating an ultrashort optical pulse.

  Here, an optical pulse (broadband light) Lw generated by a broadband light source is shown in FIG. 11A, each spectrum component thereof is shown in FIG. 11B, and each spectrum component phase-compensated for each spectrum component is shown. The generated ultrashort light pulse Lx shown in FIG. 11C is shown in FIG.

  Thus, in order to generate an ultrashort optical pulse, it is necessary not only to widen the band but also to adjust the relative phase (dispersion compensation).

  Since almost all of the actual transmission media are normal dispersion media, even if broadband light Lw0 having a constant phase of each spectral component is obtained by a broadband light source, for example, as shown in FIG. In the actually used broadband light Lw, as shown in FIG. 12B, there is positive dispersion according to the state of the broadband photogen and the material and amount of the transmission medium thereafter. As shown in (C), the realization of negative dispersion for adjusting (dispersion compensation) the relative phase of the spectrum of the broadband light Lw has been a main theme. Conventionally, dispersion compensation has been performed using a prism pair, a diffraction grating pair, and a negative dispersion mirror.

JP 2003-337309 A

However, in a spectral phase compensator that uses a conventional prism pair or diffraction grating pair and changes the distance between each pair to change the amount of negative chirp, linear chirp is attempted when a large negative chirp is added over a wide frequency spectrum range. That is, there is a problem that not only the secondary dispersion but also higher order dispersion than the secondary dispersion is added. That is, in the prism pair and the diffraction grating pair, a large positive or negative group velocity dispersion can be given to the light by using the optical path difference for each wavelength caused by refraction and diffraction. However, since higher-order phase dispersion occurs than the group velocity dispersion, precise design ranging from the design of the optical system to the selection of the optical material is required to compensate the phase over a wide band. Therefore, the phase compensation by the prism pair and the diffraction grating pair is a phase compensation means in a wavelength range substantially limited to some extent, and it is almost impossible to dynamically adjust an arbitrary phase amount.
In addition, the negative dispersion mirror is made up of a plurality of optical thin films having different refractive indexes (dielectric constants) that are alternately stacked, and the light reflected from the laminated film has a phase proportional to the frequency. Thus, since an optical material having a high damage threshold against light energy, for example, SiO ₂ or TiO ₂ is used as the dielectric multilayer film, it can withstand the use of high energy light pulses. Further, since the light pulse is only reflected by the dielectric multilayer film, the apparatus is small. The dielectric multilayer mirror formed by appropriately designing the film thickness of the deposited thin film is very easy to operate, but the band to be used is limited due to its reflection principle, and a constant function between the rotation angle and phase. Due to the relationship, the ultimate ultrashort pulse cannot be reached and the wavelength variability is limited.

  Therefore, phase compensation using conventional optical elements such as a prism pair, a diffraction grating pair, and a dielectric multilayer mirror is fixed, the phase for each spectral component of the optical pulse is known in advance, and the optical pulse It is effective only when the phase of each spectral component is invariable in time.

  In general, it is easy to add a positive chirp to an optical pulse, but adding a negative chirp requires a complicated mechanism.

  Due to recent technological innovation, the repetition frequency of ultrashort light pulses is increasing year by year, and a high repetition frequency forms a highly discrete spectrum.

  An object of the present invention is to make it possible to perform compensation of a spectral phase for generating an ultrashort optical pulse having a high repetition frequency with an inexpensive and simple device in view of the conventional situation as described above.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the embodiments described below with reference to the drawings.

  In the present invention, when performing spectral phase compensation for generating an ultrashort optical pulse having a high repetition frequency from broadband light, it is noted that an ultrashort optical pulse having a high repetition frequency has a highly discrete optical spectrum. Thus, the spectral phase is not compensated by negative dispersion as in the prior art, but the spectral phase is compensated by easily realizable positive dispersion so that the phase difference between adjacent spectra is an integral multiple of 2π.

  That is, the spectral phase compensation method according to the present invention transmits a parallel plate made of a positive dispersion medium having a thickness in which the phase difference between adjacent spectrums is an integer multiple of 2π, thereby allowing ultra-short and high repetition frequency from broadband light. Spectral phase compensation for generating optical pulses is performed.

  The spectral phase compensator according to the present invention includes a parallel plate made of a positive dispersion medium having a thickness in which the phase difference between adjacent spectra is an integral multiple of 2π, and includes a parallel plate on which broadband light is incident, and transmits the parallel plate. Thus, the spectral phase is compensated for generating an ultrashort optical pulse having a high repetition frequency from broadband light.

  Further, the spectral phase compensation method according to the present invention has a wedge-shaped cross-sectional shape, is arranged with the inclined surfaces facing each other, and at least one of the optical elements moves along the inclined surface so that the incident light is parallel to each other. A pair of optical elements made of a positive dispersion medium in which the distance between the surface and the exit surface can be changed to form a parallel plate portion adjusted to a thickness that makes the phase difference of adjacent spectra an integral multiple of 2π. By transmitting the parallel plate portion, spectral phase compensation for generating an ultrashort optical pulse having a high repetition frequency from broadband light is performed.

  The spectral phase compensators according to the present invention each have a wedge-shaped cross-sectional shape, are arranged with their inclined surfaces facing each other, and at least one of the optical elements moves along the inclined surface so that the incident light is parallel to each other. The distance between the surface and the exit surface is variable, and is composed of a positive dispersion medium that forms a parallel plate portion that can be adjusted to have a thickness that can be adjusted to a thickness in which the phase difference between adjacent spectra is an integral multiple of 2π. Spectral phase compensation is performed for generating ultrashort light pulses having a high repetition frequency from broadband light by having a pair of optical elements and transmitting the parallel plate portion.

  Further, the spectral phase compensation method according to the present invention has a wedge-shaped cross-sectional shape, is arranged with the inclined surfaces facing each other, and at least one of the optical elements moves along the inclined surface so that the incident light is parallel to each other. Broadband light is incident on a parallel plate portion having an adjustable thickness formed by a pair of optical elements made of a positive dispersion medium whose distance between the surface and the exit surface is variable, and transmitted through the parallel plate portion. Detecting light and operating a drive unit that moves at least one optical element of the pair of optical elements along a slope based on the detection output, and determining the thickness of the parallel plate part to the phase difference between adjacent spectra Is controlled to a thickness that is an integral multiple of 2π, and is transmitted through the parallel plate portion, thereby compensating the spectral phase for generating an ultrashort optical pulse having a high repetition frequency from the broadband light. The features.

  Furthermore, the spectral phase compensator according to the present invention has a wedge-shaped cross-sectional shape, is arranged with the inclined surfaces facing each other, and at least one of the optical elements moves along the inclined surfaces so that the incident light is parallel to each other. The distance between the surface and the exit surface is variable, and is composed of a positive dispersion medium that forms a parallel plate portion that can be adjusted to have a thickness that can be adjusted to a thickness in which the phase difference between adjacent spectra is an integral multiple of 2π. A pair of optical elements, a drive unit that moves at least one of the pair of optical elements along the slope, and detects the light transmitted through the parallel plate part, and the drive unit based on the detected output And controlling the thickness of the parallel plate portion to a thickness that makes the phase difference of adjacent spectra an integer multiple of 2π, and allowing the parallel plate portion to pass through to repeat from broadband light. It is characterized in that the spectral phase is compensated for generation of an ultrashort optical pulse having a high frequency.

  In the present invention, phase compensation is realized by simply transmitting through a normal dispersion medium. When the repetition frequency is in the terahertz region, the second-order phase dispersion can be eliminated with a glass material having a thickness of several centimeters. Since the light energy loss factors are only absorption of the medium and surface reflection, a high transmittance can be secured. In addition, since a normal optical glass material can be used as the dispersion medium, a spectral phase compensator with a high damage threshold can be realized. Further, according to the present invention, it is possible to realize a spectral phase compensator having a stable mechanism that does not spatially separate frequency components. Further, since it is not necessary to deposit a dielectric film or a metal film unlike ordinary optical parts, an inexpensive spectral phase compensation device can be realized.

  In other words, in the present invention, since the compensation of the spectral phase for generating the ultrashort optical pulse with a high repetition frequency is realized by a normal medium having positive dispersion, a complicated mechanism for realizing negative dispersion is required. Therefore, an inexpensive and simple spectral phase compensation device can be realized.

It is a block diagram of an ultrashort optical pulse generator provided with a spectral phase compensator composed of parallel plates to which the present invention is applied. It is a figure for demonstrating compensation of the spectrum phase by the positive dispersion in the said spectrum phase compensation apparatus. It is a block diagram of the spectrum phase compensation apparatus which consists of a pair of optical element which forms the parallel plate part to which the thickness to which this invention is adjustable is adjustable. It is a figure which shows the variable state of the thickness of the parallel plate part in the said spectral phase compensation apparatus. It is a figure which shows the specific example of a pair of optical element which forms the parallel plate part in which the thickness in the said spectral phase compensation apparatus is adjustable. It is a configuration diagram of a wideband discrete spectrum generator mounted with the spectral phase compensation device. It is a figure which shows the high-order sideband produced | generated through a Raman process in the cell for a broadband discrete spectrum production | generation of the said broadband discrete spectrum generator. It is a figure which shows each measurement result of the phase of the spectrum of the broadband light which passed the said phase compensation apparatus mounted in the said broadband discrete spectrum generator. It is a figure which shows each measurement result of the time waveform of the broadband light which passed the said phase compensation apparatus mounted in the said broadband discrete spectrum generator. It is a block diagram which shows the structure of a spectrum phase compensation apparatus provided with the function which controls automatically the thickness of a parallel flat plate part to the thickness which makes the phase difference of an adjacent spectrum the integral multiple of 2pi by a control part. It is a figure for demonstrating the production | generation method of the conventional general ultrashort light pulse. It is a figure for demonstrating the phase compensation by negative dispersion.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  The present invention is applied to, for example, the spectral phase compensator 2 in the ultrashort optical pulse generator 10 configured as shown in FIG.

  The ultrashort optical pulse generator 10 includes a broadband light source 1 that emits broadband light Lw and a spectral phase compensator 2 that receives the broadband light Lw emitted from the broadband light source 1.

  The broadband light source 1 generates a broadband light Lw by using a laser medium having a wide gain band such as a titanium sapphire crystal, or modulation of coherent light, and emits the generated broadband light Lw.

  The spectral phase compensator 2 generates an ultrashort optical pulse having a high repetition frequency from the broadband light Lw by compensating the spectral phase of the incident broadband light Lw, and generates the generated ultrashort optical pulse Lx. Is emitted.

  Here, in the case of phase dispersion compensation for a discrete spectrum that realizes an extremely high repetition period, there is an optimum condition for making the pulse width the shortest in addition to a condition in which each spectrum component has the same phase. Since the discrete spectrum is formed by equally spaced line spectra, the phase difference between adjacent spectra can be selected to be an integer multiple of 2π. By adding an appropriate secondary dispersion, it is possible to cancel the existing secondary dispersion.

  The spectral phase compensator 2 in the ultrashort optical pulse generator 10 is composed of a positive dispersion medium having a thickness t in which the phase difference between adjacent spectra is an integral multiple of 2π, and includes a parallel plate 2A on which broadband light Lw is incident. In addition, by transmitting the parallel plate 2A, the spectrum phase is compensated for generating the ultrashort optical pulse Lx having a high repetition frequency from the broadband light Lw.

  The parallel plate 2A is an optical glass having a known dispersion characteristic, the thickness t of which is adjusted according to the amount of secondary dispersion to be removed, and the secondary dispersion is compensated by inserting it into the optical path of the broadband light Lw. To do.

  That is, in this spectral phase compensator 2, as shown in FIG. 2, broadband light is transmitted by transmitting through a parallel plate 2A made of a positive dispersion medium having a thickness t in which the phase difference between adjacent spectra is an integral multiple of 2π. Spectral phase compensation is performed to generate an ultrashort optical pulse Lx having a high repetition frequency from Lw.

  Here, the spectrum and phase of the broadband light Lw generated by the broadband light source are shown in FIG. 2A, each spectral component of the broadband light Lw is shown in FIG. 2B, and phase compensation is performed for each spectral component. Each spectral component is shown in FIG. 2C, and the spectrum and phase of the generated ultrashort light pulse Lx are shown in FIG.

  In the ultrashort optical pulse generator 10, the amount of dispersion existing in the broadband light Lw incident on the spectral phase compensator 2 varies depending on the state of the broadband light source 1 and the material and amount of the transmission medium thereafter. Therefore, the parallel plate 2A of the spectral phase compensator 2 needs to have a thickness t corresponding to the amount of secondary dispersion to be removed.

  In addition, the ultrashort optical pulse generator 10 is replaced with the spectral phase compensator 2 that performs spectral phase compensation by a parallel plate 2A having a fixed thickness t, for example, a spectral phase having a configuration as shown in FIG. By using the compensator 20, the spectral phase can be compensated with an arbitrary compensation amount by the parallel plate portion 21 having a variable thickness t.

The spectral phase compensator 20 shown in FIG. 3 has a wedge-shaped cross-sectional shape, is arranged with the inclined surfaces 21A ₁ and 21B ₁ facing each other, and at least one optical element moves along the inclined surface, be freely the distance between the parallel incidence plane 21A ₂ together with the exit surface 21B ₂ variable thickness is adjusted the phase difference between adjacent spectrum thickness of an integral multiple of 2π t is adjustable parallel plate portion A pair of optical elements 21 </ b> A and 21 </ b> B made of a positive dispersion medium forming 21 is provided.

In the spectral phase compensator 20, for example, by moving the optical element 21A along the inclined surfaces 21A ₁ and 21B ₁ , the thickness of the parallel plate portion 21 is shown in FIGS. 4A and 4B. t can be freely changed. Therefore, the spectral phase can be compensated with an arbitrary compensation amount by the parallel plate portion 21.

In the spectral phase compensator 20, the adjacent spectral elements are made up of a pair of optical elements 21 A and 21 B made of a positive dispersion medium in which the distance between the entrance plane 21 A ₂ and the exit plane 21 B ₂ parallel to each other is variable. The parallel flat plate portion 21 having a thickness adjusted to an integer multiple of 2π is formed, and the parallel flat plate portion 21 is transmitted to generate the ultrashort optical pulse Lx having a high repetition frequency from the broadband light Lw. Spectral phase compensation for.

Here, when the frequency interval of the discrete spectrum is 10.6 THz, in the optical glass (BK7), if the thickness is changed by 32 mm, it is estimated that the thickness for compensating the second order dispersion appears once. length length of the optical element 21A and the short side 21B ₃ of 40mm short side 21A ₃ of the cross-sectional shape as shown in FIG. 5 is 20mm optical element 21B was manufactured by optical glass (BK7), the spectrum When the phase compensator 20 is used as the phase compensator 20 and mounted on the wideband discrete spectrum generator 30 having the configuration shown in FIG. 6 and the spectrum phase is compensated for the broadband light Lw having a discrete spectrum frequency interval of 10.6 THz, it is parallel. When the thickness t of the flat plate portion 21 is changed from 10 mm to 40 mm, the pulse width is shortened around 10 mm and 40 mm, and an ultrashort light pulse Lx is generated. Rukoto could be.

  This broadband discrete spectrum generator 30 generates a laser beam having a frequency of 372 THz (wavelength: 806.3297 nm) and a laser beam having a frequency of 383 THz (wavelength: 783.9316 nm), and is a two-wavelength laser that is coaxially superimposed and mixed. A titanium sapphire (TI: SA) laser light source 31 that emits light, and a broadband discrete spectrum generating cell 33 into which two-wavelength laser light emitted from the laser light source 31 is incident via the first half mirror 32. A first measurement system 35 in which the broadband light Lw emitted from the broadband discrete spectrum generating cell 33 is incident via a second half mirror 34, and a two-wavelength laser emitted from the laser light source 31. The light is reflected by the first half mirror 32 and incident, and the broadband discrete spectrum generating cell 3 is used. The broadband light Lw ′ emitted from the second half mirror 34 is reflected by the second half mirror 34 and is incident thereon, and is disposed between the broadband discrete spectrum generating cell 33 and the second half mirror 34. The phase compensator 20 is provided in the optical path.

  The broadband discrete spectrum generating cell 33 is, for example, a nonlinear wavelength conversion element in which a solid parahydrogen crystal is installed in an optical crystat.

  In the wideband discrete spectrum generator 30, a laser beam having a frequency of 372 THz (wavelength: 806.3297 nm) and a laser beam having a frequency of 383 THz (wavelength: 783.9316 nm) are generated by the laser light source 31 and mixed in a coaxial manner. As shown in FIG. 7, in the broadband discrete spectrum generating cell 33, the two-wavelength laser light is incident on the broadband discrete spectrum generating cell 33 as excitation laser light through the first half mirror 31. In addition, a high-order sideband is generated through a Raman process, and broadband light Lw having a frequency interval of a discrete spectrum of 10.6 THz is generated.

  As described above, the phase compensator 20 provided in the optical path between the broadband discrete spectrum generating cell 33 and the second half mirror 34 has a thickness that makes the phase difference between adjacent spectra an integral multiple of 2π. It is composed of a pair of optical elements 21A and 21B made of a positive dispersion medium forming a parallel flat plate portion 21 having an adjustable thickness t, and is incident from the broadband discrete spectrum generating cell 33. The broadband light Lw having the broadband discrete spectrum is incident on the parallel plate portion 21, and the parallel plate portion 21 performs phase compensation of each spectrum of the broadband light Lw.

  The first measurement system 35 includes a nonlinear optical element for generating harmonics in which the broadband light Lw ′ that has passed through the phase compensation device 20 is incident as the first measurement light L1 via the second half mirror 34. (BBO) 35A and a photodetector 35B for detecting harmonics generated by the nonlinear optical element (BBO) 35A.

  In the first measurement system 35, the nonlinear optical element (BBO) 35A generates a harmonic of the first measurement light L1, and the generated second harmonic (SH) is detected by the photodetector 35B. .

  The second measurement system 36 includes a delay stage 36A on which the two-wavelength laser light emitted from the laser light source 31 is reflected by the first half mirror 32 and is incident as reference light Lref. A concave mirror in which the reference light Lref is incident through the stage 36A and the broadband light Lw ′ that has passed through the phase compensation device 20 is reflected by the second half mirror 34 and incident as the second measurement light L2. 36B, a non-linear optical element (BBO) 36C for generating harmonics in which a mixed light of the reference light Lref and the second measurement light L2 is reflected by the concave mirror 36B, and the non-linear optical element (BBO) 36C It consists of spectrometer 36D into which the harmonics generated by are incident.

  The second measurement system 36 adjusts the amount of delay given to the reference light Lref by changing the optical path length through which the reference light Lref passes by the delay stage 36A, and the second measurement system 36 and the second measurement light Lref. The nonlinear optical element (BBO) 36C generates harmonics of the mixed light of the light L2, and the harmonics of the mixed light is detected by the spectrometer 36D, whereby the spectrum included in the second measurement light L2 is detected. The phase, that is, the phase of the spectrum of the broadband light Lw ′ that has passed through the phase compensation device 20 is measured.

  In the broadband discrete spectrum generating apparatus 30 having such a configuration, the thickness t of the parallel plate portion 21 of the phase compensation apparatus 20 is changed from 10 mm to 40 mm, and the broadband light Lw having a discrete spectrum frequency interval of 10.6 THz. When the thickness t of the parallel plate portion 21 is 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, and 40 mm, the second measurement system 36 passes the phase compensation device 20. The measured results of the phase of the spectrum of the broadband light Lw ′ are shown in FIG. 8 as P (10 mm), P (15 mm), P (20 mm), P (25 mm), P (30 mm), P (35 mm), P (40 mm). In addition, each measurement result of the time waveform is shown in FIG. 9 as S (10 mm), S (15 mm), S (20 mm), and S (25 mm). S (30mm), S (35mm), shown as S (40 mm).

  In FIG. 8, the phase characteristic of the spectrum of the broadband light Lw ′ without the phase compensation device 20 is shown as P (0), and the target phase characteristics are P (0π) and P (2π). , P (4π). In FIG. 9, the time waveform of the broadband light Lw ′ without the phase compensation device 20 is shown as S (0), and the time waveform in the ideal state is shown as S (R).

  As described above, in the broadband discrete spectrum generating apparatus 30, when the thickness t of the parallel plate portion 21 is changed from 10 mm to 40 mm, the pulse width becomes short near 10 mm and 40 mm, and the ultrashort light pulse Lx is generated. Could be generated.

The spectral phase compensator 20 in the broadband discrete spectrum generator 30 includes, for example, a drive unit 22 that moves the optical element 21A along the inclined surfaces 21A ₁ and 21B ₁ and the parallel as shown in FIG. Thickness that detects light transmitted through the flat plate portion 21, operates the driving unit 22 based on the detection output, and sets the thickness t of the parallel flat plate portion 21 to a phase difference of adjacent spectra that is an integral multiple of 2π. The control unit 23 can automatically control the thickness t of the parallel plate portion 21 to a thickness that makes the phase difference of adjacent spectra an integral multiple of 2π. .

The drive unit 22 has a structure in which, for example, a worm gear is rotationally driven by a pulse motor to move the optical element 21A along the inclined surfaces 21A ₁ and 21B ₁ .

  Further, the control unit 23 is the second harmonic of the first measurement light L1 detected by the photodetector 35B of the first measurement system 35, that is, the broadband light Lw ′ that has passed through the phase compensation device 20. Based on the detection output of the wave component, the pulse width, peak intensity, and the like of the broadband light Lw ′ are obtained, and the operation of the driving unit 22 is controlled, so that the thickness t of the parallel plate portion 21 is set to the broadband. The light Lw ′ is automatically controlled to have a state where the pulse width is the shortest or the peak intensity is the strongest, that is, the thickness where the phase difference of the spectrum is an integral multiple of 2π.

  The broadband discrete spectrum generator 30 detects the light transmitted through the parallel plate portion 21, operates the drive unit 22 based on the detection output, and sets the thickness t of the parallel plate portion 21 to the position of the adjacent spectrum. By providing the spectral phase compensator 20 with the control unit 23 for controlling the thickness of the phase difference to an integral multiple of 2π, the ultrashort optical pulse Lx can be generated stably and easily.

  In addition, this invention is not limited only to the above embodiment, Of course, a various change is possible in the range which does not deviate from the summary of this invention.

1 wideband HikariHara, 2 spectral phase compensator, 2A parallel plate 2A, 10 ultrashort optical pulse generator, 20 spectral phase compensator 21 parallel plate portion 21, 21A _1, 21B ₁ slope, 21A ₂ incident surface, 21B ₂ Output surface, 21A, 21B optical element, 22 drive unit, 23 control unit, 30 broadband discrete spectrum generator, 31 laser light source, 32 first half mirror, 33 broadband discrete spectrum generation cell, 34 second half mirror, 35 First measurement system, 35A Non-linear optical element (BBO), 35B photodetector, 36 Second measurement system, 36A Delay stage 36A, 36B Concave mirror, 36C Non-linear optical element (BBO), 36D spectrometer

Claims (8)

  Spectral phase compensation for generation of ultrashort optical pulses with high repetition frequency from broadband light by transmitting through parallel plates made of positive dispersion media with a thickness that makes the phase difference between adjacent spectra an integral multiple of 2π. Spectral phase compensation method characterized by performing. It is composed of a positive dispersion medium having a thickness that makes the phase difference between adjacent spectra an integer multiple of 2π, and includes a parallel plate on which broadband light is incident.
A spectral phase compensator for compensating a spectral phase for generating an ultrashort optical pulse having a high repetition frequency from broadband light by transmitting the parallel plate. Each has a wedge-shaped cross-section, and is arranged with the inclined surfaces facing each other. At least one of the optical elements moves along the inclined surface, so that the distance between the entrance surface and the exit surface parallel to each other can be varied. A pair of optical elements made of a positive dispersion medium is used to form a parallel plate portion adjusted to a thickness in which the phase difference between adjacent spectra is an integral multiple of 2π,
A spectral phase compensation method for performing spectral phase compensation for generating an ultrashort optical pulse having a high repetition frequency from broadband light by transmitting the parallel plate portion.   4. The thickness of the parallel plate portion is adjusted to a thickness that cancels second-order dispersion existing in incident broadband light and sets a phase difference between adjacent spectra to an integral multiple of 2π. The described spectral phase compensation method. Each has a wedge-shaped cross-section, and is arranged with the inclined surfaces facing each other. At least one of the optical elements moves along the inclined surface, so that the distance between the entrance surface and the exit surface parallel to each other can be varied. , Having a pair of optical elements made of a positive dispersion medium forming a parallel plate portion having an adjustable thickness that is adjusted to a thickness in which the phase difference between adjacent spectra is an integral multiple of 2π,
A spectral phase compensation apparatus for performing spectral phase compensation for generating ultrashort optical pulses having a high repetition frequency from broadband light by transmitting the parallel plate portion.   The said parallel plate part is adjusted to the thickness which cancels the secondary dispersion which exists in the incident broadband light, and makes the phase difference of an adjacent spectrum an integer multiple of 2 (pi). Spectral phase compensator. Each has a wedge-shaped cross-section, and is arranged with the inclined surfaces facing each other. At least one of the optical elements moves along the inclined surface, so that the distance between the entrance surface and the exit surface parallel to each other can be varied. Broadband light is incident on a parallel plate portion having an adjustable thickness formed by a pair of optical elements made of a positive dispersion medium,
The light transmitted through the parallel plate portion is detected, and based on the detection output, at least one optical element of the pair of optical elements is operated along a slope, and the thickness of the parallel plate portion is operated. To a thickness that makes the phase difference between adjacent spectra an integer multiple of 2π,
A spectral phase compensation method for performing spectral phase compensation for generating an ultrashort optical pulse having a high repetition frequency from the broadband light by transmitting the parallel plate portion. Each has a wedge-shaped cross-section, and is arranged with the inclined surfaces facing each other. At least one of the optical elements moves along the inclined surface, so that the distance between the entrance surface and the exit surface parallel to each other can be varied. A pair of optical elements composed of a positive dispersion medium that forms a parallel plate portion having an adjustable thickness that is adjusted to a thickness that makes the phase difference between adjacent spectra an integer multiple of 2π;
A drive unit that moves at least one optical element of the pair of optical elements along a slope;
The light transmitted through the parallel plate portion is detected, the drive unit is operated based on the detection output, and the thickness of the parallel plate portion is controlled so that the phase difference between adjacent spectra is an integral multiple of 2π. And a control unit that
A spectral phase compensation apparatus for performing spectral phase compensation for generating ultrashort optical pulses having a high repetition frequency from broadband light by transmitting the parallel plate portion.

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