JP7773200B2 - Optical measurement device and optical measurement method - Google Patents

Description

The present invention relates to an optical measurement device and an optical measurement method.

Various techniques have been developed to observe and measure high-speed phenomena. For example, strobe photography, which captures images of an object by repeatedly flashing light, is commonly used. However, strobe photography does not necessarily have a high time resolution, making it difficult to measure ultrafast phenomena on the order of f (femto) seconds ( ^10-15 seconds). One example of such an ultrafast phenomenon is the behavior of plasma generated by laser irradiation. Non-Patent Document 1 discloses a technique for measuring plasma behavior using two temporally separated probe beams generated by a Michelson interferometer.

“Single-shot two-dimensional spectral interferometry for ultrafast laser-produced plasmas” Y. Hama, K. Kondo, Z. Zoubir et al., Optics letters 31 1917 (2006).

However, the technology in Non-Patent Document 1 lacks accuracy and stability in the time delay between the two probe beams. Furthermore, because it uses an ultra-narrowband interference filter to eliminate temporal recombination, the contrast of the resulting image is far from excellent.

One aspect of the present invention aims to provide an optical measurement device and optical measurement method that improve the accuracy of measuring high-speed changes in an object.

In order to solve the above problems, one aspect of the present invention provides an optical measurement device that optically measures temporal changes in an object, and includes a first phase plate onto which polarized light is incident, a second phase plate that faces the first phase plate across the object and onto which polarized light that has exited the first phase plate and passed through the object is incident, and an analyzer onto which the polarized light exiting the second phase plate is incident, wherein the first phase plate decomposes the incident polarized light into first and second polarized light components and outputs them with a predetermined time difference, and the second phase plate eliminates the predetermined time difference between the first and second polarized light components and outputs a composite polarized light that combines the first and second polarized light components.

One aspect of the present invention provides an optical measurement device and optical measurement method that improve the accuracy of measuring high-speed changes in an object.

1 is a diagram illustrating an optical measurement device according to an embodiment of the present invention. FIG. 2 is an enlarged view of a portion of the optical measurement device. FIG. 1 is a diagram illustrating an optical measurement device for observing a laser wake generated by laser irradiation. FIG. 10 is a diagram showing the results of photographing a laser wake. FIG. 10 is a diagram showing the intensity distribution of a laser wake.

Embodiments of the present invention will now be described. Figure 1 shows an optical measurement device 10 according to an embodiment of the present invention. The optical measurement device 10 optically measures changes over time in an object OB, and functions, for example, as a microscope that magnifies and displays the object OB.

The object OB can change at ultra-high speeds (for example, on the order of f (femto) seconds, or on the order of 10 f seconds or less). One example of an object OB is a laser wake. A laser wake is a compressional wave of electron plasma that occurs when a gas is irradiated with ultra-intense laser light and travels along the propagation path of the laser light. The compressional state of the laser wake changes at extremely short time intervals. This time interval (change time Tc) is, for example, 15 f seconds.

The optical measurement device 10 includes a light source 11, a polarizer (polarizing plate) 12a, an analyzer (polarizing plate) 12b, phase plates 13a and 13b, lenses 14a to 14d, a filter 15, and an imager 16. An XYZ coordinate system is set with the direction of the optical axis A of the laser light L0 as the Z axis.

Light source 11 emits laser light L0. Light source 11 can be a continuous wave (CW) laser or a pulsed laser. For example, a titanium (Ti) sapphire laser (hereinafter referred to as a "TiS laser") can be used as a pulsed laser. A TiS laser can generate broadband, short-pulsed linearly polarized light by utilizing the nonlinear optical effect of gases.

A polarizer 12a, phase plate 13a, object OB, lens 14a, phase plate 13b, analyzer 12b, lenses 14b-14d, filter 15, and imager 16 are arranged in this order on the optical axis A of laser light L0.

The polarizer 12a and the analyzer 12b pass the linearly polarized component contained in the incident light. The polarizer 12a and the analyzer 12b have polarization axes Da and Db, respectively, and pass linearly polarized light whose polarization direction is parallel to the polarization axes Da and Db. The analyzer 12b functions as an analyzer onto which polarized light L3 emitted from the phase plate 13b (second phase plate) is incident.

The polarization axis Da of the polarizer 12a is aligned with the polarization direction of the laser light L0 emitted from the light source 11. The polarizer 12a is placed in front of the light source 11 and removes polarization components (polarization noise) contained in the laser light L0 that are perpendicular to the polarization axis Da.

The polarization axis Db of the analyzer 12b is perpendicular to the polarization axis Da of the polarizer 12a. The angle between the polarization axes Da and Db is, for example, in the range of 90°±12°. For ease of understanding, the polarization axis Da of the polarizer 12a is set to the Y-axis direction, and the polarization axis Db of the analyzer 12b is set to the X-axis direction.

The polarizer 12a and analyzer 12b can be made of, for example, a thin film or dichroic glass. As described below, when a pulsed laser is used as the light source 11, it is preferable that the polarizer 12a and analyzer 12b be made of a thin film polarizer and a dichroic glass polarizer, respectively.

The polarizer 12a is a thin-film polarizing plate in order to maintain the pulse width of the laser light L1 after it leaves the polarizer 12a. In other words, if the polarizer 12a were made of dichroic glass, the pulse waveform of the laser light would be distorted within the polarizer 12a, and the pulse width of the laser light L1 emitted from the polarizer 12a would tend to widen from the original pulse width of the laser light L0. This widening of the pulse width could hinder ultra-high-speed observation of the object OB. As described below, the pulse width PW of the laser light is preferably equal to or less than the change time Tc of the object OB. In other words, if the pulse width widens and becomes greater than the change time Tc, ultra-high-speed observation of the object OB would be hindered.

The analyzer 12b is made of dichroic glass because it has good polarization extraction properties, improving the contrast of the image. Unlike the polarizer 12a, the broadening of the pulse width caused by the analyzer 12b does not hinder the observation of the object OB at ultra-high speeds. The pulse width of the laser light becomes an issue when it passes through the object OB, and even if the pulse width broadens after passing through the object OB, it does not affect the observation of the object OB.

Note that if the effect on the pulse width of the laser light L0 from the light source 11 is small, a material other than a thin-film polarizing plate may be used for the polarizer 12a.

The above explanation is for the case where a pulsed laser with an extremely narrow pulse width (for example, on the order of fsec) is used as the light source 11. If a light source with a pulse width wider than a certain degree is used as the light source 11, or if a CW laser is used, appropriate materials can be used for the polarizer 12a and analyzer 12b. For example, both the polarizer 12a and the analyzer 12b can be dichroic glass polarizing plates.

Phase plates 13a and 13b are made of anisotropic birefringent material (e.g., birefringent crystal) and impart a phase difference to incident light. Phase plate 13a functions as a first phase plate onto which polarized light L1 is incident. Phase plate 13b faces phase plate 13a (first phase plate) across object OB. Phase plate 13b functions as a second phase plate onto which polarized light L2, which is emitted from phase plate 13a (first phase plate) and has passed through object OB, is incident.

Phase plate 13a imparts a phase difference ΔF (time difference ΔT) to the incident light. Meanwhile, phase plate 13b eliminates (reduces) the phase difference ΔF (time difference ΔT) imparted to the incident light. As described below, phase plate 13a decomposes the incident polarized light L1 into polarized light W2a and W2b (first and second polarized light, see Figure 2 described below) and emits them with a time difference ΔT (predetermined time difference). Furthermore, phase plate 13b eliminates the time difference ΔT (predetermined time difference) between polarized light W2a and W2b (first and second polarized light) and emits polarized light L3 (composite polarized light) that combines the first and second polarized light.

The phase difference ΔF and the time difference ΔT provided by the phase plate 13 a are defined by the following equations (1) and (2).
ΔF=(2π・Δn・d)/λ... Formula (1)
ΔT=c/(Δn・d)... Formula (2)
λ: wavelength of laser light L0 (center wavelength)
Δn: (anisotropic) refractive index difference of the phase plate 13a (=ne-no)
ne: refractive index in the direction of the anisotropy axis Sa of the phase plate 13a
(Refractive index for polarized light W2a (first polarized light) described below)
no: refractive index in the direction perpendicular to the anisotropy axis Sa
(Refractive index for polarized light W2b (second polarized light) described below)
d: Thickness of the phase plate 13a c: Speed of light

To eliminate (reduce) the phase difference ΔF (time difference ΔT), phase plate 13b imparts a phase difference ΔF2 and a time difference ΔT2 that are approximately the same in absolute value but opposite in sign to the phase difference ΔF and time difference ΔT (ΔF + ΔF2 ≒ 0, ΔT + ΔT2 ≒ 0). In other words, the product "Δn·d" of the anisotropic refractive index difference Δn and thickness d of phase plates 13a and 13b is approximately equal, and the anisotropy axis Sb of phase plate 13b is set to be approximately perpendicular to the anisotropy axis Sa of phase plate 13a.

The anisotropy axis Sa of the phase plate 13a forms an angle θa of approximately 45° with respect to the polarization axis Da (here, the Y axis) of the polarizer 12a, and the anisotropy axis Sb of the phase plate 13b forms an angle -θb with respect to the polarization axis Da (here, the Y axis) of the polarizer 12a (θa + θb ≈ 90°).

It is preferable that phase plates 13a and 13b are made of the same material and have the same thickness. This is because using materials with the same properties, including wavelength dependency, ensures that phase differences are imparted and eliminated. Quartz, for example, can be used as this material. For example, if the wavelength λ of laser light L0 is 800 nm, phase plates 13a and 13b can be made of quartz with a thickness of 180 μm, and the phase difference ΔF can be approximately 4π (equivalent to 2λ).

Lens 14a is disposed between object 0B and phase plate 13b (second phase plate) and functions as an objective lens for magnifying and displaying object 0B. Lens 14a can be, for example, a lens with a magnification of several to several hundred times (for example, a corrected magnification of 10 times at infinity).

Lens 14b is, for example, a tube lens, and is combined with lens 14a (objective lens) to form an image of the object OB.

Lens 14c and 14d are lenses for transferring the images formed by lenses 14a and 14b, and are used when the distance between lens 14b and imager 16 is large.

Filter 15 is a narrow-band filter for removing external light other than laser light L0 from light source 11, and has wavelength characteristics that allow light of wavelength λ of laser light L0 to pass through, but not light of wavelengths other than wavelength λ. By narrowing the bandwidth of filter 15 to, for example, 10 nanometers (full width at half maximum), the signal-to-noise ratio of the measurement can be improved.

Imager 16 is an image sensor that captures temporal changes in object OB. Imager 16 records an image that represents temporal changes in object OB, formed using polarized light with a time difference ΔT.

(Operation of the optical measuring device 10)
The operation of the optical measurement device 10 will be described below. FIG. 2 is an enlarged view of the vicinity of the phase plates 13a and 13b. In particular, the vicinity of the phase plates 13a and 13b is enlarged. FIG. 2(a) is a perspective view corresponding to FIG. 1, and FIG. 2(b) is a schematic diagram showing the state when FIG. 1(a) is viewed from the side. The operation of the optical measurement device 10 will be described below with reference to FIG. 2. Note that the lens 14a is omitted from FIG. 2 because it does not substantially affect the progression of the laser beams L1 to L4 described below.

As described above, laser light L1 is emitted from light source 11, passes through polarizer 12a, and is then incident on polarizer 12a. Specifically, laser light L1 is polarized light (electromagnetic waves) W1 that has an electric field that oscillates in the direction of the polarization axis Da of polarizer 12a (here, the Y-axis direction).

Polarized light W1 incident on phase plate 13a is separated into two polarized lights W2a and W2b, each with two different vibration directions, which then exit. Polarized light W2a vibrates in the direction of the anisotropy axis Sa of phase plate 13a, while polarized light W2b vibrates in a direction perpendicular to the anisotropy axis Sa (here, the direction of the anisotropy axis Sb of phase plate 13b). Polarized light W2a and W2b have a time difference ΔT determined by phase plate 13a. That is, polarized light W2b exits phase plate 13a first, and then, after the time difference ΔT has elapsed, polarized light W2a exits phase plate 13a.

Polarized light W2a and W2b emitted from phase plate 13a passes through object OB in sequence and reaches phase plate 13b. Here, consider two cases: (1) the state of object OB does not change during the time difference ΔT, and (2) the state of object OB changes.

If the state of the object OB does not change during the time difference ΔT, the polarized light W2a and W2b incident on the phase plate 13b are combined, eliminating the time difference ΔT. As a result, polarized light W3 (combined polarized light) is emitted from the phase plate 13b. This polarized light W3 has the same polarization state as polarized light W1 before being imparted a phase difference by the phase plate 13a. This polarized light W3 enters the analyzer 12b, and polarized light W4, which vibrates in the direction of the polarization axis Db of the analyzer 12b, is emitted. In this case, polarized light W3 is linearly polarized light vibrating in the direction of the polarization axis Da, and has no vibration component in the direction of the polarization axis Db, so the intensity of polarized light W4 is essentially zero.

On the other hand, if the state of the object OB (e.g., refractive index, transmittance) changes during the time difference ΔT, this change imparts a phase difference and intensity difference to the polarized light W2a and W2b. Therefore, when the polarized light W2a and W2b enter the phase plate 13b, the time difference ΔT is eliminated and they are combined to become polarized light W3a, which is different from polarized light W3. Unlike W3, which is linearly polarized, this polarized light W3a is generally elliptically polarized. That is, polarized light W3a has a vibration component in the direction of the polarization axis Db, i.e., an amplitude ΔIx in the direction of the polarization axis Db. As a result, polarized light W3a entering the analyzer 12b is emitted as polarized light W4a with an amplitude ΔIx.

As described above, the intensity of polarized light W4 (W4a) changes in response to changes in the state of object OB over time difference ΔT. This allows the changes in the state of object OB over time difference ΔT to be measured. In other words, polarized light W3 (synthetic polarized light) has at least one of a phase difference or intensity difference with respect to polarized light L1 that corresponds to changes in object OB over time difference ΔT (predetermined time difference). As a result, the optical measurement device 10 measures temporal changes in object OB on the order of time difference ΔT (predetermined time difference) or less.

This phase difference corresponds to a change in the refractive index or density of the object OB over a time difference ΔT (a predetermined time difference). The change in density of the object OB substantially functions as a change in the refractive index of the object OB , resulting in a phase difference, because the refractive index is a function of density in a substance such as gas or plasma whose density is much lower than the cutoff frequency.

The above explanation does not assume that laser light L0 is pulsed light. If laser light L0 is pulsed light, the operation of optical measurement device 10 can be explained as follows. That is, phase plate 13a (first phase plate) splits laser light L0 (pulsed light) into first and second pulsed light corresponding to polarizations W2a and W2b (first and second polarizations), respectively, and emits them. The first and second pulsed light pass through object OB with a time difference ΔT (a predetermined time difference). Phase plate 13b (second phase plate) eliminates the time difference ΔT, recombines the first and second pulsed light, and emits it as polarized light W3 (recombined pulsed light). Polarized light W3 (recombined pulsed light) has at least one of a phase difference or an intensity difference with respect to polarization W1 (pulsed light) that corresponds to the change in object OB over the time difference ΔT.

As described above, in this embodiment, by generating a time difference ΔT using phase plates 13a and 13b, it is possible to measure ultrafast phenomena on the order of the time difference ΔT or less. For example, by setting the time difference ΔT on the order of f (femto) seconds or less, it is possible to measure temporal changes in the object OB on the order of 10 f-seconds or less. Furthermore, it is also possible to set the time difference ΔT on the order of 0.1 p-seconds or less, and measure temporal changes in the object OB on the order of p-seconds or less.

That is, by separating polarized light W1 into polarized light W2a and W2b with a time difference ΔT, adding the inside of the object OB, and then eliminating the time difference ΔT and combining them, polarized light W4 with an intensity corresponding to the temporal change in the object OB can be obtained as a differential signal. As a result, clear time differential images of ultrafast phenomena on the f (femto) second scale can be obtained. High-precision measurements are possible using signals with high intensity and a high S/N ratio.

In this embodiment, by constructing the phase plates 13a and 13b from a birefringent material, the time difference ΔT can be made highly accurate, for example, on the order of attoseconds, using the refractive index difference (Δn = n e - n o) of the birefringent material.

It is preferable that the time difference ΔT be less than the change time Tc of the object OB. If the time difference ΔT is greater than the change time Tc of the object OB, the accuracy of measuring the temporal change of the object OB will be significantly reduced. Note that if the time difference ΔT is too small compared to the change time Tc, the S/N ratio will be small, so it is preferable to set it to a size that ensures a certain S/N ratio.

When a pulsed laser is used as the light source 11, it is preferable that the pulse width PW of the laser be equal to or less than the change time Tc of the object OB. If the pulse width PW is greater than the change time Tc of the object OB, the accuracy of measuring the change over time of the object OB decreases. In other words, by appropriately setting the upper limit of the pulse width PW, the accuracy of measuring the change over time of the object OB can be ensured. Note that if the pulse width PW is too small compared to the change time Tc, the S/N ratio will be small, so it is preferable to set it large enough to ensure a certain S/N ratio.

It is preferable to have the laser pulse width PW and time difference ΔT on the same order of magnitude. By effectively utilizing both the time difference ΔT and the pulse width PW, measurement accuracy can be improved. As shown in the examples below, for example, by dividing a laser pulse with a pulse width of 8 fsec into two pulses with a time difference ΔT of 5 fsec, it is possible to measure a change in the time interval of 15 fsec on the object OB.

By constructing phase plates 13a and 13b from the same material, the difference in wavelength dependence of phase plates 13a and 13b can be substantially eliminated. In particular, when pulsed light with a narrow pulse width is used for laser light L0, the width of the wavelength λ of laser light L0 becomes large, and the wavelength dependence of phase plates 13a and 13b can become a problem. By constructing phase plates 13a and 13b from the same material, this problem can be addressed.

(Modification)
A modified example of the present invention will now be described. In this modified example, a time differential interferometer is configured to measure changes in the object OB over time without using a lens 14a or the like for enlarging the image of the object OB.

(Example)
An example will be described below. Fig. 3 shows an optical measurement device 10 for observing laser wakes generated by laser irradiation. The optical measurement device 10 according to the example is configured by adding a light source 11a to the optical measurement device 10 according to the embodiment. Elements similar to those in Fig. 1 are given the same numbers, and descriptions thereof will be omitted.

Here, the object to be measured OB was a laser wake. That is, a laser wake was generated by irradiating the gas with ultra-high intensity laser light La from light source 11a. An electron beam E was also generated as a by-product. As mentioned above, a laser wake is a compressional wave of electron plasma formed along the propagation path of the laser light La (here, along the X-axis). Electrons are accelerated by the electric field gradient of the compressional wave and emitted as an electron beam E. Here, a laser wake with a time scale (period) of approximately 15 fsec was used.

A TiS laser with the following specifications was used as the light source 11. That is, the laser light L0 emitted from the light source 11 had a center wavelength λ of 800 nm, a pulse width PW of 8 fsec, and a maximum energy of 100 μJ.

Phase plates 13a and 13b are made of quartz crystal with a thickness of 180 μm, and the phase difference ΔF is approximately 4π (equivalent to 2λ). As a result, the time difference ΔT is 5 fsec.

Lens 14a was an objective lens with a 10x magnification at infinity, lens 14b was an aspherical tube lens with a focal length (f) of 200 mm, and lenses 14c and 14d were lenses with f=100 and 150 mm, respectively. Filter 15 was a narrow-band filter with a full width at half maximum of 10 nanometers.

Figure 4 shows the results of photographing the laser wake. Figure 5 shows the intensity distribution of the laser wake. (a) in Figures 4 and 5 shows the image and intensity distribution of the laser wake for the comparative example, and (b) for the example. The graph in Figure 5 shows the intensity distribution of the laser wake in the X-axis direction, obtained by integrating the brightness of the image in Figure 4 over the range of ΔY.

The comparative example used the shadowgraph method. That is, the phase plates 13a, 13b and analyzer 12b were removed, and an image of the laser wake was acquired by the imager 16. That is, in the comparative example, a single pulse of polarized light L1 passes through the object OB and enters the imager 16. On the other hand, in the example, the single pulse of polarized light L1 is split into two pulses of light (polarized light W2a and W2b), which pass through the object OB with a time difference ΔT, then recombine and enter the imager 16.

In the comparative example (Figure 4(a)), the image of the laser wake contains a lot of noise and is unclear. On the other hand, in the example (Figure 4(b)), the image of the laser wake is clear. This point is more clearly shown in Figure 5. In the graph of the comparative example (Figure 5(a)), the period of the laser wake is unclear, whereas in the graph of the example (Figure 5(b)), the period of the laser wake is clear.

Because laser wakes are compressional waves of electron plasma, the refractive index changes in response to changes in this compression. As a result, in this embodiment, a transient and localized phase change occurs between polarized light W2a and W2b in response to the difference in refractive index over the time difference ΔT, causing a change in the intensity of polarized light L4. On the other hand, the comparative example is unable to detect this phase difference caused by the time difference ΔT. It is believed that the comparative example detects a change in the amount of light transmitted due to the difference in refractive index itself. However, because the change in transmission is very small, the signal strength, and therefore the S/N ratio, is very small.

As such, in this example, an ultrafast phenomenon of 15 fsec was measured with higher signal strength and a higher S/N ratio than in the comparative example. This demonstrates the effectiveness of a technique that uses a pair of phase plates 13a and 13b to separate one polarized light into two polarized lights with a time difference ΔT, pass them through the object OB, and then combine them.

(Invention understood from the above embodiment and modifications)
The invention that can be understood from the above-described embodiment and modifications will be described below.

(1) An optical measurement device according to a first aspect of the present invention is an optical measurement device that optically measures changes over time in an object, and includes a first phase plate onto which polarized light is incident, a second phase plate that faces the first phase plate across the object and onto which polarized light that is emitted from the first phase plate and has passed through the object is incident, and a polarizer onto which the polarized light emitted from the second phase plate is incident, wherein the first phase plate decomposes the incident polarized light into first and second polarized light components and emits them with a predetermined time difference, and the second phase plate eliminates the predetermined time difference between the first and second polarized light components and emits a composite polarized light that is a composite of the first and second polarized light components. This makes it possible to optically measure changes over time in the object using the first and second polarized light components that pass through the object with a predetermined time difference.

(2) In the optical measurement device according to the second aspect of the present invention, the synthetic polarized light has at least one of a phase difference or an intensity difference with respect to the polarized light that corresponds to a change in the object at the predetermined time difference, and the optical measurement device measures a temporal change in the object at an order of magnitude less than the predetermined time difference. This makes it possible to optically measure a temporal change in the object using synthetic polarized light that has at least one of a phase difference or an intensity difference that corresponds to a change in the object at the predetermined time difference.

(3) In the optical measurement device according to the third aspect of the present invention, the phase difference corresponds to a change in the refractive index or density of the object at the predetermined time difference. This makes it possible to optically measure the change in the refractive index or density of the object over time.

(4) In the optical measurement device according to the fourth aspect of the present invention, the predetermined time difference is on the order of 0.1 picoseconds or less, and the optical measurement device measures changes in the object on the order of picoseconds or less. This makes it possible to measure changes in the object on the order of picoseconds or less. Alternatively, the predetermined time difference may be on the order of femtoseconds or less, and the optical measurement device may measure changes in the object on the order of 10 femtoseconds or less. This makes it possible to measure changes in the object on the order of picoseconds or less.

(5) In the optical measurement device according to the fifth aspect of the present invention, the predetermined time difference is on the order of f (femto) seconds or less, and the optical measurement device measures changes in the object on the order of 10 fsec or less. This makes it possible to measure changes in the object on the order of 10 fsec or less.

(6) In the optical measurement device according to the sixth aspect of the present invention, the predetermined time difference ΔT is defined by the following formula: ΔT = c/(Δn d), where Δn is the refractive index difference of the first phase plate for the first and second polarized light, d is the thickness of the first phase plate, and c is the speed of light. This allows the predetermined time difference ΔT to be appropriately set depending on the refractive index difference and thickness of the first phase plate.

(7) In the optical measurement device according to the seventh aspect of the present invention, the polarized light incident on the first phase plate is pulsed light, and the first phase plate splits and emits first and second pulsed light corresponding to the first and second polarized light, respectively. The first and second pulsed light pass through the object with the predetermined time difference. The second phase plate eliminates the predetermined time difference, recombines the first and second pulsed light, and emits the recombined pulsed light. The recombined pulsed light has at least one of a phase difference or an intensity difference with respect to the pulsed light that corresponds to the change in the object at the predetermined time difference. This enables more accurate measurement of changes in the object over time using pulsed light.

(8) An optical measurement device according to an eighth aspect of the present invention includes an objective lens disposed between the object and the second phase plate for magnifying and displaying the object. This allows for the configuration of a microscope for magnifying the object and observing its changes over time.

(9) In the optical measurement device according to the ninth aspect of the present invention, the first and second phase plates are made of the same material. This makes it easy to eliminate the predetermined time difference at the first phase plate by using the second phase plate, even if the polarized light incident on the first phase plate has wavelength non-uniformity. In other words, if the wavelength dependencies of the first and second phase plates are different, the predetermined time difference cannot be eliminated by using the second phase plate, even if the thicknesses of the first and second phase plates are adjusted. For example, if the polarized light is pulsed light with a narrow time width, wavelength non-uniformity is likely to be large.

(10) An optical measurement device according to a tenth aspect of the present invention is an optical measurement method for optically measuring changes over time in an object, comprising the steps of: incidenting polarized light on a first phase plate; decomposing the polarized light incident on the first phase plate into first and second polarized light having a predetermined time difference and emitting the resulting light; causing the first and second polarized light to pass through the object with the predetermined time difference; incidenting the first and second polarized light that have passed through the object on a second phase plate; and eliminating the predetermined time difference between the first and second polarized light incident on the second phase plate and emitting the resulting composite polarized light that is a composite of the first and second polarized light. This allows optical measurement of changes over time in the object using the first and second polarized light that pass through the object with the predetermined time difference.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

10 Optical measurement device 11 Light source 12a Polarizer 12b Analyzer 13a, 13b Phase plates 14a to 14d Lens 15 Filter 16 Imager

Claims (10)

An optical measurement device that optically measures temporal changes of an object on the order of p (pico) seconds or less ,
a first phase plate onto which polarized light is incident;
a second phase plate that faces the first phase plate with the object in between, and to which polarized light that has exited from the first phase plate and passed through the object is incident;
an analyzer onto which the polarized light output from the second phase plate is incident;
Equipped with
the first phase plate separates the incident polarized light into first and second polarized lights, and outputs the first and second polarized lights with a predetermined time difference of the order of 0.1 picoseconds or less ;
The second phase plate eliminates the predetermined time difference of the order of 0.1 picoseconds or less between the first and second polarized lights, and outputs a composite polarized light obtained by combining the first and second polarized lights. An optical measurement device that optically measures temporal changes of an object on the order of 10 f (femto) seconds or less,
a first phase plate onto which polarized light is incident;
a second phase plate that faces the first phase plate with the object in between, and to which polarized light that has exited from the first phase plate and passed through the object is incident;
an analyzer onto which the polarized light output from the second phase plate is incident;
Equipped with
the first phase plate decomposes the incident polarized light into first and second polarized lights and outputs them with a predetermined time difference of the order of f seconds or less;
The second phase plate eliminates the predetermined time difference of the order of f seconds or less between the first and second polarized lights, and outputs a composite polarized light obtained by combining the first and second polarized lights. An optical measurement device that optically measures a temporal change of an object,
a first phase plate, excluding a quarter wave plate, onto which polarized light is incident;
a second phase plate, excluding a quarter-wave plate, facing the first phase plate with the object in between, onto which polarized light emitted from the first phase plate and passed through the object is incident;
an analyzer onto which the polarized light output from the second phase plate is incident;
Equipped with
the first phase plate decomposes the incident polarized light into first and second polarized light and outputs them with a predetermined time difference;
The second phase plate eliminates the predetermined time difference between the first and second polarized lights and outputs a composite polarized light obtained by combining the first and second polarized lights. the composite polarized light has at least one of a phase difference or an intensity difference with respect to the polarized light, the phase difference or intensity difference corresponding to a change in the object at the predetermined time difference;
The optical measurement device according to claim 1 , wherein the optical measurement device measures a temporal change in the object on the order of the predetermined time difference or less. The optical measurement device according to claim 4 , wherein the phase difference corresponds to a change in refractive index or density of the object at the predetermined time difference. 6. The optical measurement device according to claim 1, wherein the predetermined time difference (ΔT) is defined by the following formula:
ΔT = c/(Δn d)
Δn: refractive index difference of the first phase plate for the first and second polarized lights, d: thickness of the first phase plate, and c: speed of light. the polarized light incident on the first phase plate is pulsed light,
the first phase plate splits the pulsed light into first and second pulsed light corresponding to the first and second polarized lights, respectively, and outputs the split light;
the first and second pulsed lights pass through the object with the predetermined time difference;
the second phase plate eliminates the predetermined time difference, recombines the first and second pulsed beams, and outputs the recombined pulsed beam;
the recombined pulsed light has at least one of a phase difference and an intensity difference with respect to the pulsed light, which corresponds to a change in the object at the predetermined time difference;
7. An optical measuring device according to claim 1. 8. The optical measurement device according to claim 1, further comprising an objective lens arranged between the object and the second phase plate for magnifying and representing the object. An optical measurement device described in any one of claims 1 to 8, wherein the first and second phase plates are made of the same material. An optical measurement method for optically measuring temporal changes of an object on the order of p (pico) seconds or less , comprising:
polarized light incident on a first phase plate;
a step of separating polarized light incident on the first phase plate into first and second polarized light having a predetermined time difference of the order of 0.1 picoseconds or less and emitting the separated polarized light;
a step of passing the first and second polarized lights through an object with the predetermined time difference;
The first and second polarized lights that have passed through the object are incident on a second phase plate;
a step of eliminating the predetermined time difference of the order of 0.1 picoseconds or less between the first and second polarized lights incident on the second phase plate and outputting the first and second polarized lights as a composite polarized light obtained by combining the first and second polarized lights;
An optical measurement method comprising: