JP2006308512A - Interference signal magnifying device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the intensity of an interference signal higher than that in prior art. <P>SOLUTION: This interference signal magnifying device comprises a mirror 11 for dividing light 2a with a band of one octave or more into a long wavelength component and a short wavelength component bordering on the central wavelength, mirrors 12<SB>1</SB>-12<SB>k</SB>for further dividing the light of the long wavelength component into two or more wavelength components, second harmonics generators 15<SB>1</SB>-15<SB>k</SB>for wavelength-converting the lights of respective wavelength components divided by the mirrors 12<SB>1</SB>-12<SB>k</SB>into second harmonics, and a polarizer 21 for synthesizing an interference signal by making a light of short-wavelength component interfere with two or more wavelength-converted lights. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an interference signal amplifying apparatus and method, and more particularly to an interference signal amplifying apparatus and method for amplifying the intensity of an interference signal obtained by splitting light to cause interference.

  The ultrashort pulse laser technology in the visible / near infrared wavelength region in recent years makes it possible to easily generate an ultrashort optical pulse with a full width at half maximum (pulse width) of, for example, 10 fs or less, which is very close to the light oscillation time. I came. Such an ultrashort light pulse includes only a few cycles of electric field oscillation of light in its pulse width, and is called “several cycle pulse”. For example, in the titanium / sapphire laser typically used for this several cycle pulse generation, the center wavelength is about 800 nm and the oscillation period is 2.7 fs. Therefore, assuming an optical pulse with a pulse width of 5 fs, FIG. As shown in FIG. 2, the ultrashort light pulse includes only about two periods of electric field oscillation in its pulse width.

In such a few cycle pulse, the phase of the electric field oscillation in the pulse width becomes an important parameter characterizing the optical pulse. This phase is called the optical carrier absolute phase, when the optical pulse electric field (optical carrier field) was E (t) = A (t ) cos (ωt-Δφ CE), is defined by the phase angle [Delta] [phi _CE The Here, ω represents an angular frequency of electric field vibration, t represents time, and A (t) represents an envelope function of electric field vibration having a peak value at time 0. FIG. 4 assumes that ω = 2.35 × 10 ¹⁵ [Hz], Δφ _CE = π / 2 [rad], and A (t) = shh (1.7627 t / Δτ) (Δτ = 5 [fs]). The electric field of an optical pulse of (pulse width) is shown. In this case, it can be seen that the peak of the envelope and the peak of the electric field vibration are shifted by the time of Δφ _CE / ω [s].

Further, in the mode-locked laser oscillator for emitting a laser pulse typically occurs a change in refractive index, fluctuation occurs in the optical carrier absolute phase [Delta] [phi _CE between pulses. The amount of change in the optical carrier absolute phase Δφ _CE between the pulses is called the optical carrier absolute phase offset. In the adjacent pulses, if the time width between the peaks of the envelope is t, the mode interval (repetition frequency) f _rep and t included in the laser pulse shown in FIG. There is a serious relationship.
f _rep = 1 / t (1)

Further, the frequency f _n of an arbitrary longitudinal mode is expressed by Expression (2).
f _n = n × f _rep + δ (2)
Here, n is an arbitrary integer. Further, δ is an optical carrier absolute phase offset frequency, and is expressed by Expression (3) when the optical carrier absolute phase offset is Δφ.
δ = (Δφ / 2π) × f _rep (3)
Therefore, the optical carrier absolute phase offset Δφ in the laser pulse is proportional to the optical carrier absolute phase offset frequency δ.

Considering the peak intensity of the envelope, in the case of a “multi-cycle pulse” that includes many electric field oscillations in the pulse width, the difference in peak intensity with respect to changes in the optical carrier absolute phase Δφ _CE is so small that it can be ignored. On the other hand, in the case of several cycle pulses, the difference reaches a maximum of several percent, which greatly affects optical nonlinear phenomena such as optical field ionization. In addition, the timing at which the optical nonlinear phenomenon occurs also changes. On a time scale of a few fs in a few cycle pulses, this timing change is by no means small. Therefore, it is extremely important to establish a method for controlling the optical carrier absolute phase that is stabilized for a long period of time when considering the use of ultrashort optical pulses for optical nonlinear phenomena.

In recent years, methods have been proposed for stabilizing the optical carrier absolute phase offset of mode-locked lasers. The method will be described below.
Part of the laser light emitted from the mode-locked laser oscillator is incident on the photonic crystal fiber, and white light having a bandwidth of 1 octave or more is generated using the self-phase modulation effect generated in the photonic crystal fiber. The white light is _split into a long wavelength component including the frequency F ₁ = m × f _rep + δ (m is an integer) and a short wavelength component including the frequency F ₂ = 2 × m × f _rep + δ. Subsequently, the second harmonic of the light having the frequency F ₁ included in the long wavelength component of the white light is generated. The frequency of the second harmonic is F ₃ = 2 × (m × f _rep + δ). The light of frequency F _{3 and} the light of frequency F ₂ are caused to interfere with each other, and the obtained interference signal is converted into an electric signal. Only the δ component is extracted from this electrical signal and compared with the reference signal. By controlling the refractive index in the mode-locked laser oscillator with a control circuit so that the difference between the two becomes constant, the optical carrier absolute phase offset can be stabilized (for example, see Non-Patent Document 1).

D.J.Jones, et al., SCIENCE VOL.288, 28 APRIL 2000

At present, in order to stabilize the optical carrier absolute phase offset using a general control circuit, the intensity of the interference signal needs to be 30 dB or more.
However, since the coupling efficiency of the laser light to the photonic crystal fiber is poor, an interference signal of 30 dB or more cannot be obtained unless the ratio of the light from the laser oscillator used for offset stabilization is increased. When the ratio used for offset stabilization is increased, the intensity of laser light that can be used for the intended purpose of use is inevitably reduced.
In addition, since the coupling efficiency decreases day by day due to dust adhering to the fiber end face, the optical carrier absolute phase offset cannot be stabilized for a long time.

  The present invention has been made to solve such a problem, and an object of the present invention is to make it possible to increase the intensity of the interference signal as compared with the prior art.

  In order to achieve such an object, an interference signal amplifying apparatus according to the present invention includes a spectroscopic unit that splits light in a band of 1 octave or more into three or more wavelength components, and splits light of two or more wavelength components. A wavelength conversion unit that converts the wavelength into a harmonic wave; and an interference unit that synthesizes an interference signal obtained by interfering two or more sets of the wavelength-converted light and other wavelength-converted light or spectral light. And

The interference signal amplifying apparatus according to the present invention uses a spectral means for splitting light in a band of 1 octave or more into three or more wavelength components, and two or more wavelength component lights excluding the light having the shortest wavelength component as harmonics. A wavelength conversion unit that performs wavelength conversion, and an interference unit that combines interference signals obtained by causing interference between light having the shortest wavelength component and two or more light components that have undergone wavelength conversion are provided.
In this interference signal amplifying apparatus, the center wavelength of each light wavelength-converted by the wavelength converting means is included in the shortest wavelength component.
Further, the wavelength conversion means may include two or more wavelength converters that respectively convert the wavelengths of two or more wavelength components.

The spectroscopic means includes a first spectroscopic means for splitting light having a band of 1 octave or more into a long wavelength component and a short wavelength component with a predetermined wavelength as a boundary, and light of a long wavelength component split by the first spectroscopic means. And a second spectroscopic means for splitting the light into two or more wavelength components.
For example, the boundary of splitting into a long wavelength component and a short wavelength component may be the center wavelength of light having a bandwidth of 1 octave or more, and light of a long wavelength signal may be converted into a second harmonic.

The interference signal amplifying device described above may further include an optical path length adjusting unit that adjusts an optical path length for each optical path through which light of each wavelength component split by the second spectroscopic unit passes.
In addition, an interference signal detection unit that detects an interference signal synthesized by the interference unit is further provided, and the optical path length adjustment unit can adjust the optical path length so that the intensity of the interference signal is maximized. In addition, the center wavelength after wavelength conversion by the wavelength converter can be selected so that the intensity of the interference signal is maximized.

  Further, the interference signal amplifying apparatus described above may further include a broadening unit that converts an optical pulse including an optical carrier absolute phase offset into light having a band of 1 octave or more and emits the light to a spectroscopic unit.

The method for amplifying an interference signal according to the present invention includes a step of splitting light having a band of 1 octave or more into three or more wavelength components, and light having two or more wavelength components excluding light having the shortest wavelength component as a wavelength. A step of converting, and a step of synthesizing an interference signal obtained by causing interference between the light having the shortest wavelength component and the two or more lights subjected to wavelength conversion.
Furthermore, a step of converting an optical pulse including an optical carrier absolute phase offset into light having a band of 1 octave or more may be provided.

In the present invention, light having a band of 1 octave or more is split into three or more wavelength components, and light of two or more wavelength components excluding the light of the shortest wavelength component is converted into a harmonic wave, and then the light of the shortest wavelength component is obtained. And the obtained interference signal is synthesized. Thereby, the intensity | strength of an interference signal can be enlarged using the same intensity | strength light as the past. Conversely, the light intensity required to obtain the same interference signal intensity can be reduced.
Therefore, by using the present invention for stabilizing the optical carrier absolute phase offset, the light intensity required for offset stabilization is reduced, so that most of the light can be effectively used for its intended purpose.
In addition, as a result of the increase in the intensity of the interference signal, it is possible to stabilize the optical carrier absolute phase offset for a longer time than before.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing the overall configuration of a system to which an optical carrier absolute phase offset measuring apparatus according to an embodiment of the present invention is applied.
This system includes an ultrashort pulse laser device 1, a white light generator 2, an optical carrier absolute phase offset measuring device 3, and a control circuit 4.

Here, the ultrashort pulse laser device 1 emits an ultrashort pulse laser beam 1a. For example, it is composed of a mode-locked oscillator.
The white light generation device (broadband broadening means) 2 converts the ultrashort pulse laser beam 1a incident from the ultrashort pulse laser device 1 into white light 2a having a band of 1 octave or more. For example, it is composed of a photonic crystal fiber or the like, and widens incident light using a self-phase modulation effect. “Octave” refers to an interval at which the frequency ratio of light is 2: 1.

The optical carrier absolute phase offset measuring device 3 obtains a signal indicating the optical carrier absolute phase offset frequency δ of the ultrashort pulse laser beam 1a by dispersing and interfering with the white light 2a incident from the white light generating device 2. The control signal 3a indicating the fluctuation of the optical carrier absolute phase offset frequency δ is generated by comparing this signal with a reference signal indicating the repetition frequency f _rep . A specific configuration of the optical carrier absolute phase offset measuring device 3 will be described later.

The control circuit 4 adjusts the refractive index in the ultrashort pulse laser apparatus 1 based on the control signal 3a input from the optical carrier absolute phase offset measuring device 3 so that the optical carrier absolute phase offset frequency δ is constant. . For example, the intensity of the excitation light source is modulated using an acoustic modulation element (AOM), and the refractive index in the ultrashort pulse laser device 1 is adjusted.
Thereby, the optical carrier absolute phase offset can be stabilized. For example, if the optical carrier absolute phase offset frequency δ is set to _¼ of the repetition frequency f _rep , the optical carrier absolute phase offset Δφ is π / 2 from the equation (3), so every four pulses. They can have the same relationship between the envelope and the optical carrier electric field.

Next, the configuration of the optical carrier absolute phase offset measuring device 3 will be described. FIG. 2 is a diagram illustrating a configuration example of the apparatus 3.
This device 3 spectrally separates white light 2a having a bandwidth of 1 octave or more into three or more wavelength components, converts the light of two or more wavelength components excluding the light of the shortest wavelength component into a harmonic, and then converts the light to the shortest wavelength. It has a function of amplifying the intensity of the interference signal by interfering with the component light and synthesizing the interference signal.

Specifically, the apparatus 3 includes a mirror 11 as a first spectroscopic unit, a mirror 12 ₁ to 12 _k of the k constituting the second spectroscopic unit (k is an integer of 2 or more), the optical path length K optical path length adjusters 13 _{1 to} 13 _k constituting the adjusting means, k condensing lenses 14 _{1 to} 14 _k, and k second harmonic generators 15 ₁ constituting the wavelength converting means. ˜15 _k , k collimating lenses 16 ₁ ˜16 _k , ½ wavelength plate 17 and k ½ wavelength plates 17 ₁ ˜17 _k , mirror 18, and k polarization beam splitters 19 _{1 to} 19 _k , a polarizer 20 as an interference unit, an interference signal detector 21, a reference signal detector 22, and a control signal generation circuit 23.

  The mirror 11 splits the white light 2 a having a bandwidth of 1 octave or more incident from the white light generator 2 into a short wavelength component and a long wavelength component. More specifically, the mirror 11 is a mirror that reflects the short wavelength component of the white light 2a and transmits the long wavelength component. Here, the boundary between the reflection wavelength and the transmission wavelength is the center wavelength of the spectral band of the white light 2a. For example, when the spectral band of the white light 2a is 400 to 1200 nm, the short wavelength component of 400 to 800 nm is reflected and the long wavelength component of 800 to 1200 nm is transmitted. As the mirror 11, for example, a dichroic mirror can be used. The reflection wavelength and transmission wavelength of the mirror 11 are determined in consideration of the spectrum of the white light 2a, the reflectance and transmittance of the mirror 11, the wavelength sensitivity characteristic of the interference signal detector 21 described later, and the like.

The mirrors 12 _{1 to} 12 _k further split the long wavelength component light transmitted through the mirror 11 into k wavelength components. More specifically, each of the mirrors 12 _{1 to} 12 _k is a mirror that reflects a long wavelength component and transmits a short wavelength component. However, the boundary between the reflection wavelength and the transmission wavelength is assumed that shifts by a predetermined wavelength toward the mirror 12 ₁ of the first stage to the mirror 12 _k of the last stage. When the spectral band of the white light 2a is 400 to 1200 nm, for example, the boundary wavelength of the first mirror 12 ₁ is shifted to 1170 nm, the boundary wavelength of the next mirror 12 ₂ is shifted to 1140 nm, and the boundary wavelength is shifted by 30 nm. The boundary wavelength of the final stage mirror 12 ₂ is 830 nm. As a result, the lower limit of the reflection region of the mirrors 12 _{1 to} 12 _k is shifted by 30 nm, and the long wavelength component light transmitted through the mirror 11 is further split by 30 nm. The mirror 12 ₁ to 12 _k, can be used, for example a dichroic mirror, and a notch filter. A notch filter is a filter that reflects only a certain wavelength range and transmits other wavelength ranges.

The optical path length adjusters 13 _{1 to} 13 _k are arranged on k optical paths through which the light components of the respective wavelengths separated by the mirrors 12 _{1 to} 12 _k pass, and adjust the optical path lengths of the respective optical paths.
The second harmonic generators 15 ₁ to 15 _k convert the wavelengths of the light components separated by the mirrors 12 _{1 to} 12 _k into second harmonics. Therefore, the second harmonic generators 15 ₁ to 15 _k function as wavelength converters. For each of the second harmonic generators 15 ₁ to 15 _k , the wavelength at which the intensity of the wavelength-converted second harmonic is maximized is referred to as the center wavelength of the second harmonic generator. As the second harmonic generators 15 ₁ to 15 _k , those in which the respective center wavelengths are included in the short wavelength component of the white light 2 a dispersed by the mirror 11 are used. As the second harmonic generators 15 ₁ to 15 _k , for example, a BBO crystal (barium borate crystal) can be used.
Condensing lenses 14 _{1 to} 14 _k are respectively arranged in front stages of the second harmonic generators 15 ₁ to 15 _k , and collimating lenses 16 _{1 to} 16 _k are arranged in the rear stages.

The half-wave plate 17 rotates the linearly polarized light of the short wavelength component of the white light 2 a dispersed by the mirror 11 to P-polarized light.
On the other hand, the half-wave plates 17 _{1 to} 17 _k rotate the linearly polarized light of the second harmonic light of the respective wavelength components dispersed by the mirrors 12 _{1 to} 12 _k to S-polarized light.
The mirror 18 is a mirror that totally reflects the light of the short wavelength component of the white light 2 a that is split by the mirror 11.

The polarization beam splitters 19 _{1 to} 19 _k are elements that transmit P-polarized light and reflect S-polarized light. Short-wavelength light components of the white light 2a, which is split by the mirror 11 is transmitted through the polarization beam splitter 19 ₁ ~ 19 _k because it is P-polarized light, the respective wavelength components dispersed by the mirror 12 ₁ to 12 _k Since the second harmonic light is S-polarized light, it is reflected by the polarization beam splitters 19 _{1 to} 19 _k .

The polarizer 20 passes the same polarization component of the incident P-polarized light and S-polarized light. Thus, light of the second harmonic of the wavelength components dispersed by the mirror 12 ₁ interferes with close wavelength components in the short wavelength components of the spectral white light 2a by the mirror 11. The same applies to the second harmonic light of the wavelength component dispersed by the other mirrors 12 _{2 to} 12 _k . The polarization component passing through the polarizer 20 is selected so that the intensity of the interference signal detected by the interference signal detector 21 described later is maximized.

The interference signal detector 21 detects a combination of interference signals obtained by interference of each wavelength component, and converts it into an electrical signal. As the interference signal detector 21, for example, a photodiode or a photomultiplier tube can be used.
The reference signal detector 22 detects the repetition frequency f _rep from the second harmonic light of the wavelength component dispersed by the mirror 12 _{k and} outputs an electrical signal indicating the repetition frequency f _rep as a reference signal. Note that the reference signal detector 22 may detect the repetition frequency f _rep from the second harmonic light of the wavelength component dispersed by the other mirrors 12 _{1 to} 12 _k−1 .
The control signal generation circuit 23 takes the difference between the electrical signal based on the interference signal and the reference signal and outputs the difference as the control signal 3a to the control circuit 4.

Next, the principle of amplification of interference signals by the optical carrier absolute phase offset measuring device 3 will be described.
The frequency f _n of an arbitrary longitudinal mode included in the laser pulse is expressed by Expression (2) as described above. Therefore, the frequency f ₁ of the long wavelength component of the white light 2a can be expressed by Expression (4), and the frequency f _s of the short wavelength component can be expressed by Expression (5). However, l and s are integers, and l <s.
f _l = l × f _rep + δ (4)
f _s = s × f _rep + δ (5)

In the present apparatus 3, the light of the long wavelength component is further divided into k pieces, and each wavelength component is wavelength-converted to the second harmonic. The frequencies f _l1 , f _l2 ,..., _Flk of the second harmonic can be expressed by equations (6 ₁ ) to (6 _k ), respectively. Here, l ₁ , l ₂ ,..., L _k are integers included in l.
f _l1 = 2 × (l ₁ × f _rep + δ) (6 ₁ )
f _l2 = 2 × (l ₂ × f _rep + δ) (6 ₂ )
:
f _lk = 2 × (l _k × f _rep + δ) (6 _k )
Thus, the optical carrier absolute phase offset frequency of the second harmonic is 2 × δ.

The band of the white light 2a is 1 octave or more, and the spectrum is divided into a long wavelength component and a short wavelength component with the center wavelength as a boundary, so that the short wavelength component is 2 × l ₁ × f _rep + δ, 2 × l ₂ × f. Each wavelength component of _rep + δ,..., 2 × l _k × f _rep + δ is included.
Therefore, by superimposing the light having the wavelength converted from the long wavelength component and the light having the short wavelength component, the respective wavelength components interfere with each other, and a combination of interference signals indicating the optical carrier absolute phase offset frequency δ is detected. .
As described above, in the present apparatus 3, by causing interference in two or more wavelength regions, it is possible to increase the intensity of the interference signal as compared with the conventional technique in which interference is performed in one wavelength region.

In the present apparatus 3, the optical path lengths can be adjusted by using the optical path length adjusters 13 _{1 to} 13 _k so that the intensity of the interference signal detected by the interference signal detector 21 is maximized. For example, the optical path length is adjusted so that the phases of the interference signals obtained by the interference of the wavelength components are aligned.
Similarly, the center wavelengths of the second harmonic generators 15 ₁ to 15 _k can be selected so that the intensity of the interference signal detected by the interference signal detector 21 is maximized. For example, the center wavelength is selected so that the phases of the interference signals obtained by the interference of the wavelength components are aligned.

The configuration of the apparatus 3 is not limited to that shown in FIG.
For example, in FIG. 2, the short wavelength component light of the white light 2a is converted to P-polarized light, transmitted through all the polarization beam splitters 19 _{1 to} 19 _k , and combined with the long wavelength component light. As shown in FIG. 5, the short wavelength component light of the white light 2a may be S-polarized light and combined with the long wavelength component light at the final stage of the polarization beam splitters 31 _{1 to} 31 _k . In this configuration, a half-wave plate 32 that rotates linearly polarized light into S-polarized light is disposed in the short-wavelength component optical path, and a half-wavelength plate 32 ₁ that rotates linearly polarized light into P-polarized light in each long-wavelength component optical path. to 32 _K are arranged. Reference numerals 18 ₁ to 18 _k are mirrors.

In FIG. 2, the light of the short wavelength component of the white light 2a passes through all the polarization beam splitters 19 _{1 to} 19 _k , and is long by the polarizer 20 disposed at the subsequent stage of the last stage polarization beam splitter 19 _k. Although the light interferes with configuration in which wavelength conversion of wavelength components, the short wavelength component of the white light 2a k aliquoted, each of which passes through the polarization beam splitter 19 ₁ ~ 19 _k, the polarization beam splitter 19 ₁ ~ 19 _k It is good also as a structure which interferes with the light which wavelength-converted the long wavelength component by the polarizer arrange | positioned in each latter stage. In this case, k polarizers are required, but by individually determining the polarization components that pass through each polarizer so that the intensity of each interference signal is maximized, the interference signal can be generated more than in the configuration of FIG. The sum can be further increased.

In the configuration shown in FIG. 2, a signal indicating the intensity of the interference signal detected by the interference signal detector 21 is fed back to the optical path length adjusters 13 _{1 to} 13 _k so that the intensity of the interference signal is maximized. It is also possible to automatically adjust the optical path length of each optical path.

In FIG. 2, the long wavelength component of the white light 2 a is wavelength-converted to the second harmonic and interferes with the short wavelength component, but the long wavelength component is wavelength-converted to the third and fourth harmonics. You may make it interfere. That is, it is good also as a structure which wavelength-converts into the Nth harmonic (N is an integer greater than or equal to 2) of the white light 2a, and interferes with a short wavelength component.
Furthermore, the lights wavelength-converted to the Nth harmonic may be caused to interfere with each other.
Therefore, the white light 2a is split into three or more wavelength components, the light of two or more wavelength components therein is wavelength-converted into the Nth harmonic, and the wavelength-converted light and other wavelength component light (others) The light of the wavelength component can be configured to interfere with two or more sets of light that has been wavelength-converted or light that has not been wavelength-converted.

Next, the calculation result regarding this Embodiment is shown.
Here, a titanium / sapphire laser is used, the white light generator 2 generates light having the same intensity from the spectral band 400 nm to 1200 nm, and the optical carrier absolute phase offset measuring device 3 having the configuration shown in FIG. 2 is used. Calculated for the case.

[First example]
In the first example, only dichroic mirrors are used as the mirrors 11 and 12 _{1 to} 12 _k . The characteristics of the dichroic mirror are 45 degree reflection, a reflectance of 99.5%, and a transmittance of 90%.
The mirror 11 reflects 400 to 800 nm and transmits 800 nm or more.
Subsequently, the mirror 12 ₁ reflects 1170-1200 nm and transmits 800-1170 nm. The mirror 12 ₂ reflects 1140-1170 nm and transmits 800-1140 nm. Subsequent reflection regions of the mirrors 12 _{3 to} 12 _k−1 are shifted by 30 nm, and 800 to 830 nm is reflected by the last mirror 12 _k .
This configuration has a large loss in light having a long wavelength of 800 nm or more. This takes into account that the detector is generally sensitive to the long wavelength side.
When this configuration is used, a result that the intensity of the interference signal is increased by about 9 times compared with the conventional method in which only one wavelength region is interfered.

[Second example]
In a second example, using a dichroic mirror as the mirror 11, and shall be used notch filters as a mirror 12 ₁ to 12 _k. The characteristics of the dichroic mirror are 45 degree reflection, a reflectance of 99.5%, and a transmittance of 90%. The characteristics of the notch filter are a reflectance of 99.5% and a transmittance of 70%.
The mirror 11 reflects 400 to 800 nm and transmits 800 nm or more.
Subsequently, the mirror 12 ₁ reflects 1190-1200 nm and transmits 800-1190 nm. The mirror 12 ₂ reflects 1180-1190 nm and transmits 800-1180 nm. Subsequent reflection regions of the mirrors 12 _{3 to} 12 _k−1 are shifted by 10 nm, and the last mirror 12 _k reflects 800 to 810 nm.
When this configuration was used, the result was that the intensity of the interference signal increased about 15 times compared to the conventional method.

  Even if a mode-locked laser having an oscillation wavelength different from that of the titanium / sapphire laser is used, the intensity of the interference signal can be amplified.

  The present invention can be used, for example, in the field using ultrashort optical pulses, and can suppress fluctuations in the optical carrier absolute phase offset of the ultrashort optical pulses with a minimum amount of light.

1 is a block diagram showing an overall configuration of a system to which an optical carrier absolute phase offset measuring apparatus according to an embodiment of the present invention is applied. It is a figure which shows the example of 1 structure of the optical carrier absolute phase offset measuring apparatus concerning one embodiment of this invention. It is a figure which shows the other structural example of the optical carrier wave absolute phase offset measuring apparatus concerning one embodiment of this invention. It is a figure explaining the optical carrier absolute phase of the ultrashort optical pulse in a time domain. It is a figure explaining the optical carrier absolute phase of the ultrashort optical pulse in a frequency domain.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ultra short pulse laser device, 1a ... Ultra short pulse laser beam, 2 ... White light generator, 2a ... White light, 3 ... Optical carrier absolute phase offset measuring device, 3a ... Control signal, 4 ... Control circuit, 11, 12 _{1 to} 12 _k , 18, 18 ₁ to 18 _k ... mirror, 13 _{1 to} 13 _k ... optical path length adjuster, 14 _{1 to} 14 _k ... condensing lens, 15 ₁ to 15 _k ... second harmonic generator , 16 _{1 to} 16 _k ... collimating lenses, 17, 17 _{1 to} 17 _k , 32, 32 _{1 to} 32 _k ... ½ wavelength plates, 19 _{1 to} 19 _k , 31 _{1 to} 31 _k ... polarizing beam splitter, 20 ... polarizer, 21 ... interference signal detector, 22 ... reference signal detector, 23 ... control signal generation circuit.

Claims (10)

A spectroscopic means for splitting light in a band of 1 octave or more into three or more wavelength components;
Wavelength converting means for wavelength-converting the light of the two or more wavelength components thus spectrally separated into harmonics;
An interference signal amplifying apparatus comprising: interference means for synthesizing interference signals obtained by causing two or more sets of wavelength-converted light and other wavelength-converted light or spectroscopic light to interfere with each other. A spectroscopic means for splitting light in a band of 1 octave or more into three or more wavelength components;
Wavelength converting means for wavelength-converting light of two or more wavelength components excluding light of the shortest wavelength component into harmonics;
An interference signal amplifying apparatus comprising: an interference unit configured to synthesize an interference signal obtained by causing interference between the light having the shortest wavelength component and the two or more light components subjected to wavelength conversion. The interference signal amplifying apparatus according to claim 2,
The interference signal amplifying apparatus according to claim 1, wherein a center wavelength of each light wavelength-converted by the wavelength converting means is included in the shortest wavelength component. The interference signal amplifying apparatus according to claim 2 or 3,
The interference signal amplifying apparatus, wherein the wavelength conversion means includes two or more wavelength converters that respectively convert the wavelengths of the two or more wavelength components. The interference signal amplifying device according to any one of claims 2 to 4,
The spectroscopic means includes a first spectroscopic means for splitting the light having a band of 1 octave or more into a long wavelength component and a short wavelength component with the center wavelength of the light as a boundary, and the first spectroscopic means A second spectroscopic means for further splitting light having a long wavelength component into two or more wavelength components,
The harmonic wave is a second harmonic wave. An interference signal amplifying apparatus, wherein: The interference signal amplifying device according to any one of claims 2 to 4,
The spectroscopic means includes a first spectroscopic means for splitting light having a band of 1 octave or more into a long wavelength component and a short wavelength component with a predetermined wavelength as a boundary, and the long wavelength component spectrally separated by the first spectroscopic means. A second spectroscopic means for further splitting the light into two or more wavelength components,
The interference signal amplifying apparatus further comprising: an optical path length adjusting unit that adjusts an optical path length for each optical path through which light of each wavelength component split by the second spectroscopic unit passes. The interference signal amplifying device according to claim 6,
An interference signal detection means for detecting an interference signal synthesized by the interference means;
The optical path length adjusting means adjusts the optical path length so that the intensity of the interference signal detected by the interference signal detecting means is maximized. The interference signal amplifying device according to claim 4,
An interference signal detection means for detecting an interference signal synthesized by the interference means;
The interference signal amplification apparatus, wherein the wavelength converter selects a center wavelength after wavelength conversion so that the intensity of the interference signal detected by the interference signal detection means is maximized. In the interference signal amplifying device according to any one of claims 1 to 8,
An interference signal amplifying apparatus, further comprising: a broadbanding unit that converts an optical pulse including an optical carrier absolute phase offset into light having a bandwidth of one octave or more and outputs the light to the spectroscopic unit. Spectroscopically splitting light in a band of 1 octave or more into 3 or more wavelength components;
Converting two or more wavelength components of light, excluding the light of the shortest wavelength component, into a harmonic;
Synthesizing an interference signal obtained by causing interference between the light having the shortest wavelength component and two or more light components that have undergone wavelength conversion.

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