JP2016145718A - Optical pulse train synchronization device, optical pulse train synchronization method, illumination device, detection device, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pulse train synchronization device capable of stably operating.SOLUTION: An optical pulse train synchronization device for synchronizing a first optical pulse train 21 including an optical pulse generated in a first period with a second optical pulse train 22 including an optical pulse generated in a second period includes photodetectors 5 and 6 which output a first signal corresponding to at least one of the light intensity of the first optical pulse train and the light intensity of the second optical pulse train, a photodetector 10 which outputs a second signal corresponding to a timing difference, and a control circuit 11 which outputs a control signal for adjusting at least one of the first period and the second period, so that the second signal becomes a target value obtained from the first signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical pulse train synchronizer that matches the timing of pulses in two optical pulse trains emitted by two pulse lasers.

  In a nonlinear optical microscope using a nonlinear optical process such as a stimulated Raman scattering microscope, an optical pulse train emitted by two pulse lasers is applied to a sample in a state where the pulse timings are matched (or the timing difference is kept constant). It is necessary to collect light.

  Patent Document 1 proposes a stimulated Raman scattering (SRS) microscope that detects the output of a photodetector that detects two-photon absorption as a pulse timing difference and adjusts the pulse period so that the detected value becomes a set value. doing. Patent Document 2 proposes a Coherent Anti-Stokes Raman Scattering (CARS) microscope that adjusts a pulse period based on an output difference between two photodetectors that detect a pulse timing difference.

International Publication No. 2010/140614 Pamphlet Japanese Patent No. 4862164

  In Patent Document 1, when the power of light output from a pulse laser changes, the timing difference between synchronized pulses changes, or pulse synchronization cannot be realized. Although Patent Document 2 uses two photodetectors to achieve synchronization of the optical pulse train even if the light power changes, the two photodetectors have the same sensitivity and are input to each. The power of the light to be transmitted and the pulse time width must be the same. Otherwise, optical pulse train synchronization cannot be realized, or the timing difference between the synchronized pulses changes. In addition, since the output of the photodetector largely depends on the arrangement of the focusing objective lens and the light receiving surface of the photodetector, the arrangement of the objective lens and the photodetector must be complicatedly matched between the two photodetectors. Don't be.

  It is an object of the present invention to provide an optical pulse train synchronization device, an optical pulse train synchronization method, an illumination device, a detection device, and a program that can operate stably.

  The optical pulse train synchronizer of the present invention synchronizes the first optical pulse train including the optical pulse generated in the first cycle and the second optical pulse train including the optical pulse generated in the second cycle. A first detector that outputs a first signal corresponding to at least one of the light intensity of the first optical pulse train and the light intensity of the second optical pulse train; Second detection means for outputting a second signal corresponding to a timing difference between an optical pulse included in the pulse train and an optical pulse included in the second optical pulse train; and the second signal is the first signal Control means for outputting a control signal for adjusting at least one of the first period and the second period so as to obtain a target value obtained from the signal.

  It is an object of the present invention to provide an optical pulse train synchronization device, an optical pulse train synchronization method, an illumination device, a detection device, and a program that can operate stably.

1 is a block diagram of an optical pulse train synchronization apparatus of the present invention. Example 1 It is a graph showing the output voltage of the photodetector 10 shown in FIG. Example 1 It is a time profile of each intensity | strength when the 1st optical pulse train and 2nd optical pulse train which are shown in FIG. 1 synchronize. Example 1 1 is a block diagram of an optical pulse train synchronization apparatus of the present invention. (Example 2) It is a graph showing the output voltage of the photodetector 10 shown in FIG. (Example 2) It is a conceptual diagram of the SRS microscope using the optical pulse train synchronizing device shown in FIG. (Example 3) It is a time profile of each intensity | strength of the 1st optical pulse train and the 2nd optical pulse train in the SRS microscope shown in FIG. (Example 3)

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is an optical path diagram of an optical pulse train synchronizer (hereinafter simply referred to as “synchronizer”) according to the first embodiment. The synchronization device includes a first optical pulse train 21 emitted from a pulse laser (first light source means) 1 and a second optical pulse train emitted from a pulse laser (second light source means different from the first light source means) 2. 22 is synchronized. The synchronization device, the pulse laser 1 and the pulse laser 2 constitute an illumination device that illuminates the sample.

  An optical pulse train is a series of optical pulses emitted by a pulse laser. That is, the synchronizer maintains a constant timing difference between the arrival of the optical pulse included in the first optical pulse train 21 and the optical pulse included in the second optical pulse train 22. The wavelength (λ1) of the first optical pulse train 21 and the wavelength (λ2) of the second optical pulse train 22 are different from each other.

  The pulse length of the pulse laser 1 can be changed, and the pulse period (first period) of the first optical pulse train 21 can be adjusted. The first period is adjusted according to the timing difference of the pulse, and the ratio of the pulse period (second period) of the second optical pulse train 22 to the first period is accurately set to an integer to an integer. Timing can be matched. The first optical pulse train includes optical pulses generated in the first period, and the second optical pulse train includes optical pulses generated in the second period.

  The beam splitter 3 reflects a part of the light beam emitted from the pulse laser 1 in the right direction and transmits the rest in the downward direction. The beam splitter 4 reflects a part of the light beam emitted from the pulse laser 2 in the downward direction and transmits the rest in the right direction. Since the beam splitters 3 and 4 need only be able to reflect incident light at a certain rate, a glass flat plate can be used. Further, a flat plate coated with a predetermined reflectance or a polarizing beam splitter may be used.

  The photodetector 5 receives the light reflected by the beam splitter 3 and acquires a signal proportional to the power of the incident light (first optical pulse train 21). That is, the photodetector 5 functions as light intensity detection means (first detection means) that outputs a signal (first signal) corresponding to the light intensity of the first optical pulse train 21. The photodetector 6 receives the light reflected by the beam splitter 4 and acquires a signal proportional to the power of the incident light (second optical pulse train 22). That is, the photodetector 6 functions as light intensity detection means (first detection means) that outputs a signal (first signal) corresponding to the light intensity of the second optical pulse train 22.

  The photodetectors 5 and 6 include a light receiving element such as a photodiode or an avalanche photodiode and an electric circuit that converts a current generated in the light receiving element into a voltage. As will be described later in Example 2, it is sufficient that at least one of the photodetectors 5 and 6 is provided. In other words, the light intensity detecting means only needs to detect at least one of the light intensity of the first optical pulse train 21 and the light intensity of the second optical pulse train 22.

  The dichroic mirror 7 transmits the first optical pulse train 21 and reflects the second optical pulse train 22 to multiplex the first optical pulse train 21 and the second optical pulse train 22 coaxially. The dichroic mirror 7 uses a dielectric multilayer film designed to transmit light of wavelength λ1 and reflect light of wavelength λ2.

  The beam splitter 8 demultiplexes the first optical pulse train 21 and the second optical pulse train 22 combined by the dichroic mirror 7 in two directions. A part of the incident light is reflected and used in the synchronization device, and the rest of the incident light is transmitted and used in a system that requires a synchronized optical pulse train such as a nonlinear optical microscope.

  Since the beam splitter 8 only needs to reflect incident light at a constant rate, a glass flat plate can be used. Further, a flat plate coated with a predetermined reflectance may be used, or a polarizing beam splitter may be used.

  The first optical pulse train 21 and the second optical pulse train 22 reflected by the beam splitter 8 are condensed on the light receiving surface of the photodetector 10 by the objective lens 9. In order to increase the two-photon absorption signal detected by the photodetector 10, the objective lens 9 preferably has a numerical aperture of 0.5 or more.

  The photodetector 10 is a timing difference detection signal (second signal) corresponding to a timing difference between the light pulse included in the first light pulse train 21 and the light pulse included in the second light pulse train 22 reaching the light receiving surface. It functions as a timing difference detection means (second detection means) that outputs. The photodetector 10 includes, for example, a light receiving element such as a photodiode and an electric circuit that converts a current generated in the light receiving element into a voltage and outputs the voltage. In order to obtain a two-photon absorption signal, the light receiving element of the photodetector 10 has a photon energy (E1∝1 / λ1) of the first optical pulse train 21 and a photon energy (E2∝1 / λ2) of the second optical pulse train 22. ), That is, the wavelength λ1 · λ2 / (λ1 + λ2) corresponding to E1 + E2. When λ1 is 1030 nanometers and λ2 is 800 nanometers, it is sufficient that the sensitivity of light detection is 450 nanometers.

  FIG. 2 shows the output voltage (vertical axis) of the photodetector 10 and the timing at which the second optical pulse train 22 arrives at the light receiving surface from the timing at which the first optical pulse train 21 arrives at the light receiving surface of the photodetector 10. It is a graph which shows the relationship of the difference (horizontal axis) which subtracted.

  In addition to the two-photon absorption signal corresponding to E1 + E2, the output (timing difference detection signal) of the photodetector 10 includes a two-photon absorption signal corresponding to E1 + E1 and E2 + E2. The two-photon absorption signal corresponding to E1 + E1 and E2 + E2 gives an offset to the two-photon absorption signal corresponding to E1 + E2. Two-photon absorption corresponding to E1 + E1 and E2 + E2 occurs in the first and second periods, respectively, but the band frequency of the output voltage of the photodetector 10 is set smaller than the frequency corresponding to these periods. The output voltage is a DC component (offset).

  The two-photon absorption signal corresponding to E1 + E2 is generated when the timings of the first optical pulse train 21 and the second optical pulse train 22 coincide (that is, when the light-receiving surface of the photodetector 10 is reached at the same time). When the peak intensities of the two pulses completely match, the maximum signal is obtained, which is proportional to the product of the power of the first optical pulse train 21 and the power of the second optical pulse train 22. That is, the maximum value of the two-photon absorption signal corresponding to E1 + E2 can be expressed as a0 · V1 · V2 using the proportionality coefficient a0, the output voltage V1 of the photodetector 5, and the output voltage V2 of the photodetector 6.

  Similarly, a two-photon absorption signal corresponding to E1 + E1 can be expressed as a1 · V1 · V1 using proportional coefficients a1 and V1, and a two-photon absorption signal corresponding to E2 + E2 is expressed as a2 using proportional coefficients a2 and V2. -It can be expressed as V2 / V2.

  The proportional coefficients a0, a1, and a2 can be easily calculated from the data corresponding to FIG. 2 acquired using an oscilloscope or a data logger and the output voltages of the photodetectors 5 and 6, and stored in the storage means. ing.

  The output voltage of the photodetector 10, the output voltage of the photodetector 5, and the output voltage of the photodetector 6 are input to the control circuit 11. The control circuit 11 is a control means for outputting a signal for pulse synchronization to the pulse period adjusting means 12 based on the input voltage, and is constituted by a microcomputer. The control circuit 11 has at least one of the first period and the second period so that the output voltage (second signal) of the photodetector 10 becomes a target value obtained from the first signal represented by the following equation. A control signal for adjusting the signal is output to the pulse period adjusting means 12. That is, the control circuit 11 inputs a control signal to at least one of the pulse lasers 1 and 2.

Target value = a0 / 2 · V1 · V2 + a1 · V1 · V1 + a2 · V2 · V2 (1)
That is, the control circuit outputs a control signal for adjusting at least one of the first cycle and the second cycle (here, the first cycle) so that the timing difference detection signal becomes the target value VA. . The target value is not limited to VA.

  The control circuit 11 has storage means for storing information on the target value of the output voltage of the photodetector 10, and this target value can be rewritten. For this reason, the storage means is composed of, for example, an EEPROM. The target value information includes, for example, Equation (1) and proportional coefficients a0, a1, a2, and ε.

  The pulse period adjusting means 12 is constituted by a stage to which a phase modulator or a mirror is attached, and adjusts the resonator length of the pulse laser 1 by applying a voltage to the phase modulator or driving the stage. The first period is changed by adjusting the resonator length, and the pulse timing can be adjusted. Further, the pulse period adjusting means 12 may be installed not in the pulse laser 1 but in the pulse laser 2 to adjust the resonator length of the pulse laser 2. In the present invention, it is only necessary to provide a pulse period adjusting means for adjusting at least one of the first period and the second period.

  The control circuit 11 controls the first cycle so that the timing difference indicated by the alternate long and short dash line in FIG. 2 is obtained. The relationship between the intensity (vertical axis) and time t (horizontal axis) of the first optical pulse train 21 and the second optical pulse train 22 on the light receiving surface of the photodetector 10 during pulse synchronization is shown in FIG. Shown in a) and (b). When pulse synchronization is realized, the timing difference between the intensity peak of the specific optical pulse 21A of the first optical pulse train 21 and the intensity peak of the specific optical pulse 22A of the second optical pulse train 22 is the pulse shown in FIG. It coincides with the timing difference TD when synchronized. When the pulse synchronization is continuously realized, the optical pulse 22B of the optical pulse train 22 is applied to the light receiving unit of the photodetector 10 with the timing difference shown in FIG. 2 for the optical pulse 21B adjacent to the optical pulse 21A. To reach.

  In FIG. 3, the ratio of the pulse periods of the first optical pulse train 21 and the second optical pulse train 22 is 2: 1. However, the ratio of the pulse periods of 2: 1 is an example, and the present invention has a pulse period ratio of It can be applied in the case of m: n. However, m and n are arbitrary natural numbers, respectively.

  When the output voltage of the photodetector 10 is higher than the target value VA, the optical pulse 21A and the optical pulse 22A are closer to each other than in the pulse synchronization state shown in FIG. Therefore, the control circuit 11 outputs a signal for reducing the first period (decreasing the resonator length) to the pulse period adjusting unit 12 so that the first optical pulse train 21 advances. Conversely, when the output voltage of the photodetector 10 is lower than the target value VA, the control circuit 11 increases the first period so that the first optical pulse train 21 is delayed with respect to the second optical pulse train 22. Such a signal (which increases the resonator length) is output to the pulse period adjusting means 12. In the signal output to the pulse period adjusting unit 12, the band and the amplitude of the voltage are set so that the control is stably performed in the vicinity of the region indicated by the one-dot chain line in FIG.

  With the above-described control, the first optical pulse train 21 and the second optical pulse train 22 are maintained at a constant timing difference on the light receiving surface of the photodetector 10.

  Here, the behavior of the synchronization device when the output power of the pulse laser 1 or the pulse laser 2 is changed will be considered. In the conventional synchronizer, the target value VA is a fixed value. The relationship between the output voltage of the photodetector 10 and the pulse timing difference when the output power decreases is shown by a broken line in FIG. Not only does the two-photon absorption signal corresponding to E1 + E2 decrease, but the two-photon absorption signal corresponding to E1 + E1 and E2 + E2 giving the offset voltage also decreases. As a result, the output voltage of the photodetector 10 does not reach the target value VA set before the output power is reduced, and pulse synchronization cannot be performed. If the change amount of the output power is small, the pulse timing difference changes according to the change of the output power even if the pulse synchronization can be performed. For this reason, in the conventional synchronization device, when the power of light input to the synchronization device is changed, there is a problem that the pulse synchronization cannot be continued or the pulse synchronization is not stable (the pulse timing difference is not constant).

  Therefore, the control circuit 11 changes (adjusts) the target value VA to the target value VB indicated by the two-dot chain line in FIG. 2 based on the detection results of the photodetectors 5 and 6. Even if the power of light input to the synchronization device changes due to the change of the target value, the pulse synchronization can be continued and the pulse timing difference can be kept constant.

  The control circuit 11 changes information of at least one of the detection results of the photodetectors 5 and 6 and information on the target value stored in the storage means (in this embodiment, equation (1), proportional coefficients a0, a1, a2). A target value is calculated based on (calculation step). The calculation step is always performed in the present embodiment, but may be performed every time the detection results of the photodetectors 5 and 6 change or may be performed periodically. Thereby, the target value is updated as needed. The target values VA and VB are both expressed by Equation (1). In addition, since the timing difference TD is also maintained at this time, Equation (1) also has a function of maintaining a predetermined timing difference.

  In Equation (1), the proportional coefficient of the first term is a0 / 2 as the most stable value of pulse synchronization, but pulse synchronization is possible even if it is set to other values within the range of 0 to a0. . When the proportionality coefficient a0 / 2 is set to the proportionality coefficient a3 (= a0 · ε), the formula (1) is modified as follows. ε is a value in the range of 0 to 1, and the pulse synchronization is most stable at 1/2 or the vicinity thereof.

Target value = a3.V1.V2 + a1.V1.V1 + a2.V2.V2 (1 ')
By adjusting the proportionality coefficient of the first term in the range of 0 to a0, the timing difference between the first optical pulse train 21 and the second optical pulse train 22 on the light receiving surface of the photodetector 10 can also be adjusted. By changing the timing difference on the light receiving surface of the photodetector 10, it is possible to change the timing difference of the optical pulse train that is transmitted through the beam splitter 8 and used in the nonlinear optical microscope. The timing difference can also be adjusted by making a difference between the first optical pulse train 21 and the second optical pulse train 22 in the optical path length from the dichroic mirror 8 to the light receiving surface of the photodetector 10. For example, a pulse timing difference can be adjusted by inserting a delay adjustment mechanism or glass block composed of a stage and a mirror between the dichroic mirror 8 and the objective lens 9.

  An optical pulse train synchronization method for synchronizing the first optical pulse train generated in the first period and the second optical pulse train generated in the second period, which is executed by the control circuit 11, also constitutes one aspect of the present invention. To do. The optical pulse train synchronization method includes a step of outputting a signal for adjusting at least one of the first period and the second period to the pulse period adjusting means so that the timing difference detection signal becomes a target value. The optical pulse train synchronization method is executed by a computer and includes a calculation step and an output step. In the calculation step, a target value is calculated from the first signal corresponding to at least one of the light intensity of the first optical pulse train 21 and the light intensity of the second optical pulse train 22. The second signal corresponds to the timing difference between the optical pulse included in the first optical pulse train 21 and the optical pulse included in the second optical pulse train 22. In the output step, a control signal for adjusting at least one of the first period and the second period is output to the pulse period adjusting means 12 so that the second signal becomes the target value. In this embodiment, it is not necessary to determine that the second signal shown in FIG. 2 has changed from the solid line state to the broken line state, and the target value is reset based on the change in the first signal to adjust the pulse period. Therefore, the calculation load of the control circuit 11 is small. A program for causing a computer to execute the optical pulse train synchronization method also constitutes one aspect of the present invention. Such a program may be stored, for example, on a non-transitory computer readable medium.

  FIG. 4 is a block diagram of the synchronization device of the second embodiment. In this embodiment, the beam splitter 4 and the photodetector 6 shown in FIG. 2 are not used, and a laser with stable output light power is used as the pulse laser 2. In this case, since the power of the optical pulse train 22 is constant, a0 · V2 can be regarded as a constant b0 in the two-photon absorption signals a0 · V1 · V2 corresponding to E1 + E2 shown in FIG. Similarly, the two-photon absorption signal a 2 · V 2 · V 2 corresponding to E 2 + E 2 can be regarded as a constant b 1. That is, in Example 2, the output voltage of the photodetector 10 is expressed as shown in FIG.

  The proportional coefficients b0, a1, and b1 are the data corresponding to FIG. 5 acquired using an oscilloscope or a data logger, the output voltage of the photodetector 5 when the optical pulse train 21 is shielded, and the light pulse train 22 when shielded. It can be calculated based on the output voltage of the photodetector 5. The proportional coefficients b0, a1, and b1 can be stored in the storage unit. In the second embodiment, pulse synchronization can be realized in the same manner as in the first embodiment by setting the target values VA and VB of the output voltage of the photodetector 10 as shown in Expression (2).

Target value = b0 / 2 · V1 + a1 · V1 · V1 + b1 (2)
In the same manner as in the first embodiment, when the proportional coefficient b0 / 2 is set to the proportional coefficient b2 (= b0 · ε), the formula (2) is modified as follows. ε is a value in the range of 0 to 1, and the pulse synchronization is most stable at 1/2 or the vicinity thereof.

Target value = b2 · V1 + a1 · V1 · V1 + b1 (2 ′)
According to the first and second embodiments, the timing difference between the first optical pulse train 21 and the second optical pulse train 22 is kept constant. The second embodiment stabilizes pulse synchronization even when the light receiving element of the photodetector 10 has no sensitivity to two-photon absorption of E2 + E2 due to characteristics such as a band gap, that is, has no sensitivity at half the wavelength of λ2. There is an effect to make it. In this case, since the two-photon absorption signal (a2 · V2 · V2) corresponding to E2 + E2 is constant at zero, the output voltage V2 of the photodetector 6 is used to cope with the change in the two-photon absorption signal of E2 + E2. There is no need. That is, the pulse synchronization can be stably performed even if the photodetector 6 is omitted. However, since the two-photon absorption signal (a0 · V1 · V2) corresponding to E1 + E2 cannot be changed, if the power (V2) of the second optical pulse train 22 changes, the first optical pulse train 21 and the second optical pulse train 21 The pulse timing difference of the optical pulse train 22 changes.

  In Patent Document 2, two detectors that detect a two-photon absorption signal are used as the pulse timing difference, and the optical pulse train is synchronized by control using the difference between the signals of the two detectors. The two-photon absorption signal depends on the power of the irradiated light, the pulse width, and the alignment (of the objective lens and the detector light-receiving surface), and in Patent Document 2, these must be complicatedly matched by the two detectors.

  In the first and second embodiments, the photodetector that detects a two-photon absorption signal that is sensitive to alignment is a simple configuration having only one photodetector 10, and photodetectors 5 and 6 (or only the photodetector 5). Can be used to stably synchronize the optical pulse train even if the optical power changes.

  FIG. 6 is a block diagram of a microscope system (detection apparatus) according to the third embodiment. The microscope system includes an SRS microscope 100 and an optical pulse train synchronization device 200. The SRS microscope 100 combines two optical pulse trains of different wavelengths emitted from two pulse lasers 1 and 2, collects the sample 105 and simultaneously irradiates stimulated Raman scattering (SRS) light generated by irradiating the sample 105. To detect. That is, the SRS microscope 100 is a type of nonlinear optical microscope that irradiates a sample with two optical pulse trains of different wavelengths emitted from two pulse lasers and observes the sample using a nonlinear optical process. The synchronization device 200 synchronizes the optical pulse trains emitted from the two pulse lasers 1 and 2.

  SRS is one of nonlinear optical phenomena and is generated in proportion to the product of the intensity of light of each wavelength. In order to efficiently generate SRS, the light beams of the lasers having two wavelengths are condensed at the same point, and the optical pulse trains are synchronized so that the optical pulse trains of the two wavelengths are simultaneously condensed. When SRS occurs, the intensity of the optical pulse train having the shorter wavelength of the two optical pulse trains becomes weaker, and the intensity of the optical pulse train having the longer wavelength becomes stronger. In order to efficiently generate SRS, it is desirable to use a short pulse laser having a pulse time width of 1 to 10 picoseconds.

  As the pulse lasers 1 and 2, an optical pulse train having a pulse period of 2: 1 is used. FIG. 7A shows a first optical pulse train 21 generated by the pulse laser 1, and FIG. 7B shows a second optical pulse train 22 generated by the pulse laser 2. In both FIG. 7A and FIG. 7B, the horizontal axis represents time (t), and the vertical axis represents light intensity. It is assumed that the wavelength (λ1) of the first optical pulse train 21 is larger than the wavelength (λ2) of the second optical pulse train 22.

  As the pulse laser 1, an ytterbium-doped fiber laser having a center wavelength of 1030 nanometers and a pulse period of 25 nanoseconds is used. As the pulse laser 2, a solid-state laser (titanium sapphire laser) having a center wavelength of 800 nanometers and a pulse period of 12.5 nanoseconds is used. For example, Specai-Physics Mai Tai is used.

  When the first optical pulse train 21 and the second optical pulse train 22 have the same timing and are collected at the same point on the sample, as shown in FIGS. 7A and 7B, the SRS As a result, the light intensity of the optical pulse train transmitted through the sample changes. The intensity of the light pulses 41, 43, and 45 in FIG. 7B decreases, and the intensity of the light pulses 42 and 44 does not change. Since the difference in the intensity of the adjacent pulses is very small, it is detected by synchronous detection.

  The detected intensity difference corresponds to the SRS signal, and the information on the molecules contained in the spot where the light beam is focused is reflected. For example, when the difference (c / λ2−c / λ1) between the resonance frequency of the molecular vibration contained in the point and the optical frequency of the two lasers coincides, the SRS signal becomes large. c is the speed of light. A Raman spectrum can be acquired by acquiring the SRS signal while changing the difference (c / λ2-c / λ1) between the optical frequencies of the two lasers. In order to obtain a Raman spectrum, the wavelength of at least one of the two lasers is changed. It can be estimated from the Raman spectrum what kind of molecules are contained in the sample. The SRS microscope can acquire a spectrum equivalent to a microscope using spontaneous Raman scattering. Since the scattering efficiency of SRS is much higher than that of spontaneous Raman scattering, the SRS microscope can acquire a Raman spectrum in a shorter time than a microscope using spontaneous Raman scattering.

  The light beams emitted from the pulse lasers 1 and 2 enter the synchronization device 200, and the first optical pulse train 21 and the second optical pulse train 22 are synchronized so that their timings coincide with each other in the sample observed with the SRS microscope. Is done. The optical pulse train 21 and the optical pulse train 22 that are coaxially combined by the dichroic mirror 7 pass through the beam splitter 8 and enter the SRS microscope 100.

  The SRS microscope 100 is configured as a laser scanning microscope. The light beams of the two pulse lasers are coaxially incident on the beam scanner 101, deflected by the beam scanner 101, and emitted. The beam scanner 101 includes a galvano scanner and a resonant scanner, and changes the direction of the optical axis in two orthogonal directions. For simplification of the drawing, the two mirrors in the beam scanner 101 are represented by one mirror in FIG. If a resonant scanner (scan frequency 8 kHz) and a galvano scanner (scan frequency 15 Hz) are used, an image of 500 lines can be acquired at 30 frames per second.

  The light beam deflected by the beam scanner 101 enters the objective lens 104 through the lenses 102 and 103. By arranging the lenses 102 and 103 so that the entrance pupils of the beam scanner 101 and the objective lens 104 are conjugate, even if the light beam is deflected by the beam scanner 101, the amount of light is collected on the sample 105 without being changed by light shielding. Shine. The magnification of the optical system using the lenses 102 and 103 is selected so that the entrance pupil size of the objective lens 104 is equal to the incident light beam size. Then, the light spot size condensed by the objective lens 104 can be minimized, and the spatial resolution for detecting the SRS signal can be improved. Further, since the SRS signal is increased by increasing the intensity of the light spot, the SN ratio for detecting the SRS signal is also improved. The objective lens 104 preferably has a large numerical aperture (NA) from the viewpoint of the spatial resolution for detecting the SRS signal and the signal-to-noise ratio.

  The sample 105 is sandwiched between a cover glass and a slide glass (not shown). The light spot focused on the sample 105 is two-dimensionally scanned by the deflection of the light beam by the beam scanner 101, and the SRS signal is converted into a two-dimensional image. Since the SRS signal is generated only at the condensed light spot, a three-dimensional image can be obtained by moving the sample 105 in the optical axis direction by a stage not shown.

  The objective lens 106 has an NA that is equal to or greater than the NA of the objective lens 104 so as to receive all the light transmitted through the sample 105 and subjected to intensity modulation by the SRS. The light beam emitted from the objective lens 106 passes through the filter 107 and the lens 108 and is then irradiated on the light receiving surface of the photodiode 109. The filter 107 is composed of a dielectric multilayer film, blocks light of wavelength λ1, and transmits light of wavelength λ2. The photodiode 109 is irradiated with a light pulse that is emitted from the pulse laser 2 and repeats the intensity modulation by SRS for each pulse, and the photodiode 109 detects this. As the photodiode 109, a silicon photodiode having sensitivity to light of 800 nanometers having a cutoff frequency of 40 MHz or more is used.

  For the repetition frequency 80 MHz (pulse period 12.5 nanoseconds) of the optical pulse train 22 of the pulse laser 2, the intensity modulation by SRS is 40 MHz (period 25 nanoseconds). The current-voltage conversion circuit 110 is an electric circuit for outputting a current signal generated by the photodiode 109 as a voltage.

  The synchronous detection circuit 111 extracts the amplitude of a 40 MHz component from the voltage signal output from the current-voltage conversion circuit 110 and outputs it as a voltage, and uses a mixer circuit or a lock-in amplifier. The output voltage of the synchronous detection circuit 111 indicates how much SRS has occurred at the focal point of the sample 105.

  The computer 112 uses the control signal of the beam scanner 101 to convert the output signal (SRS signal) of the synchronous detection circuit 111 into a two-dimensional image and display it. The computer 112 can also display a three-dimensional image of the SRS signal acquired by moving the sample 105 in the optical axis direction on a stage (not shown). The computer 112 can also display a Raman spectrum from the SRS signal acquired by changing the wavelength of at least one of the two pulse lasers.

  The present invention may be applied to an application in which a first optical pulse train including an optical pulse generated in a first cycle and a second optical pulse train including an optical pulse generated in a second cycle are synchronized. it can.

5, 6... Photodetector (first detection means), 10... Photodetector (second detection means), 11... Control circuit (control means), 21... First optical pulse train, 22. Optical pulse train, 200 ... Optical pulse train synchronizer, VA, VB ... Target value

Claims (15)

An optical pulse train synchronizer that synchronizes a first optical pulse train including an optical pulse generated in a first cycle and a second optical pulse train including an optical pulse generated in a second cycle,
First detection means for outputting a first signal corresponding to at least one of the light intensity of the first optical pulse train and the light intensity of the second optical pulse train;
Second detection means for outputting a second signal corresponding to a timing difference between arrival of an optical pulse included in the first optical pulse train and an optical pulse included in the second optical pulse train;
Control means for outputting a control signal for adjusting at least one of the first period and the second period so that the second signal becomes a target value obtained from the first signal;
An optical pulse train synchronizer comprising:   The output voltage of the first signal corresponding to the light intensity of the first optical pulse train is V1, the output voltage of the first signal corresponding to the light intensity of the second optical pulse train is V2, and the proportionality coefficient is a1. , A2, and a3, the target value obtained from the first signal is represented by a3 · V1 · V2 + a1 · V1 · V1 + a2 · V2 · V2. Synchronizer.   3. The optical pulse train synchronizer according to claim 2, wherein the proportional coefficient a3 is represented by a0 · ε using the proportional coefficients a0 and ε, and ε is a value in a range of 0 to 1. 4. The optical pulse train synchronizer according to claim 3, wherein ε is ½. The light intensity of the second optical pulse train is constant;
The output voltage of the first signal corresponding to the light intensity of the first optical pulse train is V1, the output voltage of the first signal corresponding to the light intensity of the second optical pulse train is V2, and the proportionality coefficient is a1. , B1 and b2, the target value obtained from the first signal is represented by b2 · V1 + a1 · V1 · V1 + b1. 2. The optical pulse train synchronizer according to claim 1, wherein   6. The optical pulse train synchronizer according to claim 5, wherein the proportional coefficient b2 is expressed by b0 · ε using the proportional coefficients b0 and ε, and ε is a value in the range of 0-1. The optical pulse train synchronizer according to claim 6, wherein ε is ½.   The control means inputs the control signal to at least one of a first light source means for generating the first pulse train and a second light source means for generating the second pulse train. 8. The optical pulse train synchronizer according to any one of 1 to 7.   9. The optical pulse train synchronizer according to claim 1, wherein the second detection unit includes a photodiode that converts a current generated by two-photon absorption into a voltage. 10.   The optical pulse train synchronizer according to claim 9, further comprising an objective lens for condensing the first optical pulse train and the second optical pulse train on a light receiving surface of the photodiode.   The optical pulse train synchronizer according to any one of claims 1 to 10, a first light source means for generating the first pulse train, a second light source means for generating the second pulse train, A lighting device comprising:   12. A detection apparatus comprising: the illumination apparatus according to claim 11; and light receiving means for detecting light whose intensity is modulated by irradiating the sample with the first and second optical pulse trains.   13. The detection apparatus according to claim 12, wherein the light receiving unit detects light whose intensity is modulated by stimulated Raman scattering generated by irradiating the sample with the first and second optical pulse trains. An optical pulse train synchronization method for synchronizing a first optical pulse train including an optical pulse generated in a first cycle and a second optical pulse train including an optical pulse generated in a second cycle,
A calculation step of calculating a target value from a first signal corresponding to at least one of the light intensity of the first optical pulse train and the light intensity of the second optical pulse train;
The second signal corresponding to the timing difference between the arrival of the optical pulse included in the first optical pulse train and the optical pulse included in the second optical pulse train is the target value calculated in the calculation step. An output step for outputting a control signal for adjusting at least one of the first period and the second period;
An optical pulse train synchronization method comprising:   A program for causing a computer to execute the optical pulse train synchronization method according to claim 14.