JP3197007U - Laser oscillator - Google Patents

Abstract

Provided is a laser oscillation device capable of stabilizing resonance even when the finesse of an optical resonator is increased, and generating stronger laser light by accumulating laser light in the optical resonator. An excitation laser light source composed of a laser diode LD, an optical isolator 3, and a demultiplexer / multiplexer WDM, and a fiber that generates laser light having a desired wavelength when the laser light is supplied from the laser light source. An optical isolator that is interposed between the amplifier, the optical resonator, the optical resonator and the fiber amplifier, guides the laser light from the fiber amplifier to one of the optical resonators, and blocks the laser light in the reverse direction; An optical circuit that takes in laser light emitted from the other side of the resonator, returns it to the optical resonator via a fiber amplifier and an optical isolator, and promotes resonance; a modulator that modulates the laser light in the optical circuit; Is provided. [Selection] Figure 2

Description

  The present invention provides a laser oscillator capable of generating a strong laser beam by using a self-oscillation system including an optical storage resonator so that a higher peak intensity can be obtained by operating a pulse. The present invention relates to an oscillation device.

  In recent years, small light source devices utilizing laser Compton scattering have been developed. The intensity of such a light source device as a light source depends on the intensity of the laser target that can be realized. When a pulsed linear accelerator is used as a base, a high-intensity pulse laser is used as the laser beam, or a method of temporarily amplifying the burst is used.

  On the other hand, if the average intensity of the laser is to be increased by a continuous operation system based on a storage ring type device using a Compton scattering or a superconducting accelerator, a high-intensity laser target is required continuously.

  For this reason, in a conventional X-ray generator (see, for example, Patent Document 1) that generates X-rays by laser inverse Compton scattering when a laser beam and electrons collide, a known high-intensity mode-locked oscillator, for example, 500 W A strong laser beam is generated by using a laser generator having a high-intensity mode-locked oscillator having a performance of 10 psec / pulse, wavelength “1064 nm”, and repetition frequency “150 MHz” and an optical storage resonator.

  Here, the optical storage resonator is an optical resonator that confines the laser light in a space in which the optical path is closed by a plurality of mirrors, effectively increasing the intensity of light from a relatively low-power laser light source, and continuously This is a promising technology that can realize high-intensity laser light.

  FIG. 22 shows a configuration example of a conventional laser storage device. The output from the laser oscillator is stored in an external resonator prepared independently. In order for light to accumulate in the optical resonator, the condition that a standing wave occurs in the optical resonator, that is, the mirror interval matches an integral multiple of a half wavelength must be satisfied. The resonance width is determined by the reflectivity of the resonator mirror, and becomes narrower as a higher reflectivity mirror is used to obtain a higher increase rate. In a resonator with an increase rate of 1000 times, the resonance width becomes sub-nanometer in terms of the position accuracy of the resonator mirror, and the resonance state is easily lost due to environmental disturbances such as vibration. In order to control the resonance conditions mechanically and maintain the laser accumulation state, it is necessary to perform advanced feedback control by piezo driving the resonator mirror. At present, the technical limit for stably maintaining resonance is an increase rate of about 1000 times.

JP 2009-16488 A

  However, since the high-strength mode-locked oscillator used in such a conventional laser oscillation apparatus is very expensive, there is a problem that the laser oscillation apparatus itself is also expensive. In addition, in the conventional laser oscillation device, it is difficult to require an advanced technique for controlling the resonance state of the optical resonator with high accuracy, which determines the technical limit of the increase rate. .

  Furthermore, in the conventional laser oscillation device, when the laser pulse generated by the high-intensity mode-locked oscillator is guided to the optical storage resonator and stored, unless the feedback control accuracy is considerably high, the laser pulse can be stored stably. There was a problem that I could not. In addition, the conventional laser oscillation apparatus has a problem that it can only store and amplify about 1000 times, and the laser pulse energy in the optical storage resonator is only about 100 μJ / pulse.

  For this reason, even if the finesse (accumulation amplification factor) of the optical resonator is increased, the present invention stabilizes the resonance and accumulates the laser beam in the optical resonator, so that a stronger laser beam can be obtained compared to the conventional case. It is an object of the present invention to provide a laser oscillation device capable of generating.

  In order to achieve the above object, a laser oscillation apparatus according to the present invention includes a laser light source that generates laser light for excitation, a fiber amplifier that generates laser light having a desired wavelength from the laser light, and the fiber amplifier. An optical resonator that resonates and accumulates the laser light generated by the optical amplifier, and a mode-locked amplitude that amplitude-modulates the laser light, wherein the fiber amplifier and the optical resonator are formed as an optical circuit that resonates the laser light. A modulator is provided on the input side of the fiber amplifier.

  As a first embodiment of the present invention, a laser light source for generating excitation laser light, a fiber amplifier for generating laser light of a desired wavelength from the laser light, and the fiber amplifier generated by the fiber amplifier An optical resonator for resonating and accumulating laser light; an optical isolator disposed on the output side of the fiber amplifier for guiding the laser light to one of the optical resonators and blocking reverse laser light; and the fiber amplifier The optical resonator and the optical isolator are formed as an optical circuit for resonating the laser light, and active-modulate the laser light by a modulation signal adjusted to an integral multiple of a frequency corresponding to the optical circuit length. Provided is a laser oscillation device in which a mode-locked amplitude modulator is provided on the input side of the fiber amplifier.

  As a second embodiment of the present invention, a laser light source for generating laser light for excitation, a fiber amplifier for generating laser light of a desired wavelength from the laser light, and the fiber amplifier generated by the fiber amplifier An optical resonator for resonating and accumulating laser light; an optical isolator disposed on the output side of the fiber amplifier for guiding the laser light to one of the optical resonators and blocking reverse laser light; and the fiber amplifier The optical resonator and the optical isolator are formed as an optical circuit that resonates the laser light, monitors the output of the optical isolator, and the laser light is transmitted by the frequency signal of the laser light that circulates the optical circuit. A laser having a reproduction mode-locked amplitude modulator for amplitude modulation provided on the input side of the fiber amplifier Providing isolation device.

  Here, the reproduction mode lock type amplitude modulator includes a photodiode for extracting a part of the laser light from the fiber amplifier, a first RF amplifier for amplifying an output signal of the photodiode, and the RF A bandpass filter for extracting an RF signal of a desired frequency band to be grown from the output signal of the amplifier, a phase modulator for performing phase modulation of the RF signal that has passed through the bandpass filter, and the phase modulated signal And a second RF amplifier that drives the amplitude modulator with an RF signal.

  A second fiber amplifier for generating laser light having a desired wavelength from the laser light is disposed in the optical circuit.

  An adjustment cable for finely adjusting the optical path length of the optical circuit can be provided on the optical circuit.

  As another embodiment of the present invention, there is provided a laser oscillation apparatus for generating pulsed light by forming an optical resonator and a plurality of fiber amplifiers in an optical peripheral circuit, and generates laser light for excitation. The laser generated by the laser light source, including a laser light source and a mode-locked amplitude modulator that amplitude-modulates light having a desired frequency that is an integral multiple of the frequency corresponding to the optical path length of the optical circuit and is desired to grow A first fiber amplifier that emits a pulse laser beam having the desired frequency upon entering light; an optical resonator that resonantly accumulates the pulse laser beam emitted from the first fiber amplifier; and the pulse laser beam. A second fiber amplifier for amplifying the pulsed laser light emitted from the optical resonator, and an adjustment cable adapted to the wavelength of A first photodiode for extracting a part of the laser light from the amplifier, a splitter for dividing the output signal of the first photodiode into two, and amplifying one of the two output signals from the splitter A first RF amplifier, a bandpass filter for extracting an RF signal of the laser beam having the desired frequency from the output signal of the first RF amplifier, and phase modulation of the RF signal that has passed through the bandpass filter. A phase modulator to perform, a second RF amplifier to drive the amplitude modulator with the phase-modulated RF signal, a second photodiode to monitor the other of the two output signals from the splitter; The pulsed laser light is composed of the first fiber amplifier, the optical resonator, and the second fiber amplifier. The self-oscillation is amplified by circulating around the optical circuit and accumulated in the optical resonator, and the adjustment cable is a cable for finely adjusting the optical path length of the optical circuit in the optical circuit. A laser oscillation device characterized by the above is provided.

  The optical resonator is preferably a Fox Smith interferometer type resonator having at least two concave mirrors facing each other at a predetermined interval.

  Furthermore, it is preferable that the optical resonator includes a piezo adjuster that finely adjusts the length of the resonator formed by the two concave mirrors in correspondence with the laser light having the desired wavelength.

  The fiber amplifier is preferably formed by the optical fiber having a core doped with Yb.

  In addition, the laser oscillation device of the present invention is characterized by generating laser light for a light source using laser Compton scattering.

  As a result, the laser oscillation device according to the present invention can stabilize the resonance even if the finesse of the optical resonator is increased, and can generate a strong laser beam by accumulating the laser beam in the optical resonator. Is made possible.

The concept of a circular oscillation type optical storage device is shown. 1 shows a configuration of a laser oscillation device based on circular oscillation type light accumulation according to a first embodiment of the present invention. The system when adjusting the optical system of the free space part of this apparatus is shown. The result of having measured the signal of PD1 by the spectrum analyzer by the resonator mirror without a coat | court by the modulator off is shown. The result of having measured the signal of PD1 with the spectrum analyzer by the resonator mirror without a coat | court by the modulator ON is shown. An oscilloscope observation waveform of the PD1 signal when the modulator is on with an uncoated resonator mirror is shown. The result of having measured the signal of PD1 with the resonator mirror of 90% reflectance in the modulator off by the spectrum analyzer is shown. The observation result of the noise peak by the spectrum analyzer measurement of PD1 when the reproduction mode is locked by this apparatus is shown. The pulse waveform which observed PD1 with the oscilloscope when the reproduction | regeneration mode lock by this apparatus is shown is shown. The result of having measured the signal of PD1 with the modulator OFF in the resonator mirror of 99% reflectance with the spectrum analyzer is shown. The result of having measured the signal of PD1 with the spectrum analyzer by the resonator mirror of 99% reflectance with the modulator on is shown. A pulse waveform obtained by observing PD1 with an oscilloscope with a 99% reflectance resonator mirror and a modulator on is shown. A configuration of a laser oscillation apparatus adopting a reproduction mode lock method for amplitude modulation of laser light is shown. The result of having measured the signal of PD1 by the spectrum analyzer by the resonator mirror without a coat | court by the modulator off is shown. The result of having measured the monitor signal by the oscilloscope by the resonator mirror without a coat with a modulator off is shown. The result of having measured the signal of PD1 with the spectrum analyzer by the resonator mirror without a coat | court by the modulator ON is shown. The result of having measured the signal of PD1 with the oscilloscope with the modulator on by the resonator mirror without a coat is shown. The result of having measured the signal of PD1 with the resonator mirror of 90% reflectance in the modulator off by the spectrum analyzer is shown. The waveform of the PD1 signal when the modulator is off with a 90% reflectivity resonator mirror is shown. The result of having measured the signal of PD1 by the spectrum analyzer by the resonator mirror of 90% reflectance in the modulator ON is shown. The waveform of the signal of PD1 when the modulator is on with a resonator mirror of 90% reflectivity is shown. The configuration of a conventional laser storage device is described.

  Hereinafter, the present invention will be described in detail based on preferred embodiments thereof with reference to the accompanying drawings.

1. DESCRIPTION OF THE FIRST EMBODIMENT OF THE INVENTION FIG. 1 is a diagram for explaining the concept of a circular oscillation type optical storage device that is a self-oscillation system, in which an optical resonator and a laser amplifier are integrated as a whole. It is characterized by the configuration points. Since the oscillation circuit itself automatically follows the resonance condition, there is an advantage that the resonance state continues without control. If the gain at the amplifier exceeds the circulation loss including the resonator, the system enters an oscillation state, and the laser light automatically continues to circulate in the optical circuit. Oscillation begins with the spontaneous emission light noise of the amplifier. Spectral components of the noise light that happen to be accepted by the resonance width of the optical resonator pass through the optical resonator, become the seed light thereafter, and are amplified in the loop, eventually exciting the laser amplifier. All of the energy is concentrated in this component, and the system is in a steady state where the amplifier is saturated.

  It differs from the conventional method in that the resonator unit and the amplifying unit are integrated to form a laser oscillator. In the conventional method, the resonance condition is canceled due to vibration or the like by using high-speed and high-accuracy feedback technology, whereas in the new method, the oscillation circuit itself automatically follows the resonance condition. Even if not, there is an advantage that the resonance state continues.

  In order to compensate for the loss of a complicated optical path transmitted through the resonator, a high gain amplifying unit is required, and a fiber amplifier capable of obtaining a high gain with a single path becomes the key to the development of this system. Therefore, the basic research of the optical storage resonator and the high-efficiency fiber laser amplification method led to the idea of a closed optical system (circular oscillation) that caused self-oscillation. In such a high finesse type optical resonator, only the resonating laser light is accumulated, so stable laser light amplification is achieved by returning the laser light that has passed through the optical resonator to the high-efficiency fiber laser amplifier. Together with this, laser light accumulation is realized.

  Then, it was confirmed that the laser beam resonated with the optical resonator can be amplified by the high-efficiency fiber laser amplifier, and the laser beam obtained by stable amplification can be accumulated in the optical resonator.

  At this time, it was confirmed that a laser beam having energy more than 10,000 times the energy of the laser beam incident on the optical resonator was present in the optical resonator.

  Then, an optical resonator is arranged in the exit path of the accelerator that accelerates the electron beam, the electron beam sufficiently accelerated by the accelerator is guided to the exit path, and directly collides with the laser light in the optical resonator, It was confirmed that a soft X-ray to a gamma ray beam can be generated.

  FIG. 2 shows a laser oscillation apparatus according to a first embodiment of the present invention. In FIG. 2, an optical resonator and a free space optical system in the right half are arranged with the optical resonator interposed therebetween. A pair of matching lens groups 1 and 2 and a pair of collimator lenses respectively positioned at the input and output ends are provided. The left half of the fiber optical system includes an adjustment cable, a demultiplexer / multiplexer (WDM), The optical isolator, the fiber amplifier, and the amplitude modulator are connected by a fiber to form a closed loop with the free space optical system.

  Two fiber amplifiers are provided in order to have a sufficient gain for satisfying the oscillation condition, and both fiber amplifiers 1 and 2 are Yb fiber amplifiers. A Yb fiber is a double clad type fiber with a core doped with Yb. When a laser beam of a predetermined wavelength (excitation laser beam) is supplied and excited, a Yb fiber emits a laser beam having a different wavelength. Generate and supply.

  In order to define the rotating direction, the optical isolators 1 and 2 are inserted in two places. The optical isolator passes the laser beam supplied to the terminal and emits it from the terminal.

  A laser light source that generates laser light for excitation includes a laser diode LD, an optical isolator 3, and the aforementioned demultiplexer / multiplexer (WDM). The laser diode is composed of a semiconductor laser element that generates laser light having a wavelength necessary to excite the fiber amplifier, and generates laser light when a drive voltage is applied. → Supply to the optical isolator through the path of the optical isolator terminal.

  The optical isolator 3 is configured so that the laser beam supplied to the terminal passes through and is emitted from the terminal, and the laser beam supplied to the terminal is blocked and does not exit from the terminal. Is taken in, passed through the optical fiber connected to the terminal, emitted from the terminal, and demultiplexed / multiplexed by a path of terminal → optical fiber → demultiplexer / multiplexer terminal. Supply to the multiplexer. Further, when the laser beam is emitted from the demultiplexer / multiplexer and supplied to the terminal via the optical fiber, it is blocked to protect the laser diode.

  When a laser beam having a first wavelength and a laser beam having a second wavelength are incident from one of the terminals, the demultiplexer / multiplexer synthesizes and emits the light from the other terminal. When the laser light combined from the terminal is incident, it is demultiplexed, and the demultiplexed laser light is emitted from the terminal and emitted from the terminal. When light is output and supplied to a terminal connected to the optical fiber, the laser light is taken in and supplied to the fiber amplifier 2 connected to the terminal. When the laser light is emitted from the fiber amplifier 2 and supplied to the terminal, the laser light is demultiplexed, and the laser light having the divided wavelength is emitted from the terminal, and the demultiplexer / multiplexer terminal → The optical fiber is supplied to the optical isolator through the path of the optical fiber → optical isolator terminal.

  Further, the optical isolator 2 is configured to take in the laser beam supplied to the terminal, pass it and emit it from the terminal, and to block the laser beam supplied to the terminal so as not to emit from the terminal. When the laser beam emitted from the demultiplexer / multiplexer is supplied through the path of the wave / multiplexer terminal → optical fiber → terminal, this is passed through, and the terminal → optical fiber → amplitude modulator → fiber amplifier. 1 → The optical isolator 1 is supplied to the optical system through a path. Also, the optical isolator 1 is cut off when laser light is supplied from the optical system through a path of optical system → optical fiber → terminal so that the laser light does not return to the demultiplexer / multiplexer.

  The optical path length of the optical circumference circuit is provided with an adjustment cable for finely adjusting the optical path length of the optical circumference circuit, and this adjustment cable is also constituted by a fiber.

  The adjustment cable and the fiber amplifier are nonpolarization-preserving, but a paddle type polarization controller is inserted because the polarization plane needs to be matched to the polarization-maintaining system after the modulator. A 10% coupler is installed at the end of the fiber system, and a part (10%) of the circulating light is taken out and monitored by a photodiode (PD). In order to cause pulsing in the active mode lock system, the amplitude modulator is driven by an RF signal applied from the outside.

  The matching lens group 1 is connected to the fiber via the collimator lens 1 and includes a plurality of mirrors that reflect the laser light and a matching lens that adjusts the diameter of the laser light, and the like. While taking in and reflecting, the diameter, the deflection direction, and the like are adjusted, and the electron beam is made incident on an optical resonator arranged in the output path of the accelerator that accelerates the electron beam.

  The optical resonator is attached to a resonator structure (not shown) disposed in an exit path of an accelerator that accelerates an electron beam, and a resonator structure having a reflectance of 90% or more and a radius of curvature of 250 mm. A concave mirror that is attached to the resonator structure so that the concave mirror is spaced apart from the concave mirror by a distance corresponding to the wavelength of the laser beam and the concave side faces the concave mirror. And a piezo element which is arranged between the back surface of the substrate and the resonator structure and deforms in accordance with the applied voltage and adjusts the position and mounting angle of the concave mirror, and the like. When laser light is supplied from the group 2 to the back surface of each concave mirror, the phase is adjusted while transmitting through each concave mirror and confining and accumulating it between the concave mirrors. In parallel with this operation, a part of strong laser light accumulated between the concave mirrors is emitted from the concave mirrors and supplied to the matching lens group 1 and the matching lens group 2.

  The matching lens group 2 is connected to the fiber via the collimator lens 2 and includes a plurality of mirrors that reflect the laser light and a matching lens that adjusts the diameter of the laser light, and captures and reflects the supplied laser light. While adjusting the diameter, deflection direction, etc., the light is incident on the optical resonator. Further, the laser light emitted from the optical resonator is taken in and reflected, and the diameter, the deflection direction, and the like are adjusted, emitted from the collimator lens 2, and supplied to the terminal of the output coupler via the optical fiber.

  As described above, the light exits from the fiber to the free space from the collimator lens 1 and is adjusted by a pair of lenses for matching before entering the optical resonator. By adjustment described later, the optical resonator length is adjusted to 420 mm (frequency 357 MHz). A micrometer stage is attached to one resonator mirror and used for fine adjustment of the optical resonator length, and the other optical resonator mirror is piezo-driven and used for scanning during adjustment. After passing through the optical resonator, the light passes through a symmetric optical system and is input again from the collimator lens 2 to the fiber. On the way, a part is reflected by the beam sampler, PD2 monitors the reflected light of the resonator, and PD3 monitors the transmitted light of the optical resonator.

  Each part is monitored by PD1 to PD3, and it is necessary to associate the power to be monitored at this time with the power in each part of the optical circuit. The reason for this is that although the oscillation wavelength in this apparatus is around 1035 nm, calibration is required when it differs from the wavelength of each element such as a commercially available resonator mirror. In this case, as the monitor point of the optical circuit, the ASE light generated by exciting the fiber amplifier 1 is used to measure and associate the power of each part.

  In the above configuration, adjustment of the optical resonator repetition frequency and adjustment of the optical circuit for performing the pulse operation of the self-oscillation system will be described.

  In order to determine the optical system in the free space, adjustment is performed using, for example, a 714 MHz mode-locked laser. First, the aim is to accurately determine the resonator length of the optical resonator. The resonator has a configuration of FSR = 357 MHz in which concave mirrors having a curvature radius of 250 mm are faced to each other at 420 mm intervals.

  As shown in FIG. 3, the light from the mode-locked laser is transported through a fiber, connected to a collimator with an FC / APC connector, and emitted. At this time, the optical resonator length is adjusted with a micrometer so that the resonance is maximized while adjusting the light passing through the optical resonator. In the matching, the fiber connection is switched between the forward direction and the reverse direction, and the matching between the upstream side and the downstream side is adjusted independently. The signal is input from the forward direction and re-input to the fiber on the output side, and the entire optical system matching is confirmed.

  Next, adjustment of the optical circuit will be described. The mirror of the optical resonator can be replaced with an uncoated substrate of the same shape, and in this case, the optical path length corresponding to the optical resonator length passes, but the resonance phenomenon does not occur. Here, a slight mismatch in matching can be recovered by finely adjusting the mirror of the fiber re-input portion. This basically results in a simple ring laser configuration. When the fiber amplifier is turned on with the amplitude modulator turned off and the signal of the photodiode PD1 is measured with a spectrum analyzer, a super mode noise peak corresponding to the optical path length of the circuit can be observed. In this state, adjustment of the paddle of the polarization controller and adjustment of the DC offset of the amplitude modulator are performed so as to maximize the peak intensity. In this configuration, since the fundamental frequency of the circulation is about 6.5 MHz, harmonics 55 times the fundamental frequency are used to match this with the target 357 MHz. The length of the adjustment cable is adjusted so that the 55th peak coincides with 357 MHz. In this example, the adjustment can be made up to 357.067 MHz. In order to increase the accuracy, it is also possible to use a piezo stretcher and a delay line. In addition, when viewed in a wide span, super mode noise peaks can be confirmed at intervals of 6.49 MHz.

  By such an adjustment, when a 357 MHz RF signal adjusted to an integral multiple of the frequency corresponding to the optical circuit length is input to the amplitude modulator and pulsated, the modulated 357 MHz component becomes stronger and other noise peaks are generated. Is suppressed, and a pulse structure is completed with the period of modulation. That is, as a result of introducing an amplitude modulation in which a free space storage resonator adjusted to a repetition frequency of 357 MHz is incorporated into a fiber amplifier system whose loop optical path length is adjusted to 55 times and oscillated, the circular light corresponds to the resonator length. It has a pulse structure with a stable interval, and at the same time, the intensity increases inside the storage resonator.

  This confirmation can be made by measuring the signal of PD1 with a spectrum analyzer and confirming that the modulated 357 MHz component is strengthened and pulsates and oscillates.

  The resonator mirror has a reflectance of 90% or 99% at a wavelength of 1064 nm. Similarly, ASE light was incident and the transmittance was measured. The 90% mirror had a transmittance of 7.5%, and the 99% mirror had a transmittance of 1.3%. In this explanation, they are called 90% mirror and 99% mirror, but when the power inside the resonator is actually estimated from the power transmitted through the resonator, it is calculated from the transmittance of the measurement result.

  The verification of this device will be described. Measured with the amplitude modulator on and off (when the cable to the amplitude modulator is disconnected from the coupler) for each case where the resonator mirror of the optical resonator is uncoated and 90% and 99% reflective The results are shown.

a) Results with an uncoated resonator mirror FIG. 4 shows the results of measuring the PD1 signal with a spectrum analyzer when the modulator is off. According to FIG. 4A, a super noise peak is seen in the vicinity of 357 MHz. In addition, according to the measurement in FIG. 4B, which is observed in a wide span, super mode noise peaks can be observed at intervals of 6.5 MHz.

  FIG. 5 shows a spectrum analyzer measurement result of the PD1 signal when the modulator is on. FIG. 5B shows that a 357 MHz component subjected to modulation is strengthened and other noise peaks are suppressed according to FIG. The pulse waveform of FIG. 6 obtained by observing PD1 with an oscilloscope indicates that a pulse structure is formed with a modulation period.

b) Result with 90% Reflectance Resonator Mirror FIG. 7 shows the result of measuring the signal of PD1 with a spectrum analyzer when the modulator is off. According to FIG. 7A, a peak is seen in the vicinity of 357 MHz, and FIG. 7B shows that no super mode noise peak is observed even in a wide span. This is because other peaks are suppressed by the resonator structure.

  FIG. 8 shows a measurement result of the spectrum analyzer of the signal of PD1 when the modulator is on. FIG. 8 (a) and FIG. 8 (b) seen in a wide span show that the modulated 357 MHz component becomes stronger and pulsates and oscillates. The pulse waveform of FIG. 9 obtained by observing PD1 with an oscilloscope indicates that a more stable pulse train is formed than in the case of no coating.

c) Result with 99% reflectivity resonator mirror FIG. 10 shows the result of measuring the signal of PD1 with a spectrum analyzer when the modulator is off. According to FIG. 10A, a peak is observed in the vicinity of 357 MHz, and FIG. 10B shows that no super mode noise peak is observed even when viewed in a wide span.

  FIG. 11 shows the measurement result of the spectrum analyzer for the signal of PD1 when the modulator is on. FIG. 11 (a) and FIG. 11 (b) viewed from a wide span show that the 357 MHz component subjected to modulation becomes stronger and oscillates in a pulsed manner. The pulse waveform of FIG. 12 obtained by observing PD1 with an oscilloscope indicates that a more stable pulse train is formed than in the case of no coating.

2. Description of the Second Embodiment of the Present Invention In the description of the first embodiment of the present invention, harmonic pulsing is performed by forcibly applying amplitude modulation to the laser oscillator system using an external signal generator. It was. This system has a relatively simple configuration and can easily change the harmonics to be oscillated.

  On the other hand, in the second embodiment to be described, instead of using an external modulation signal generator, the noise of the laser oscillator itself is electrically extracted and the amplitude modulator is driven to obtain the fundamental frequency of the system. It is possible to feed back an exactly matched modulation signal. According to this method, even if the oscillation frequency itself fluctuates, the relationship between the modulation signal and the loop length can be obtained by using the reproduction mode lock method, which is made by reproducing the drive signal of the amplitude modulator from its own oscillation signal. Therefore, pulse oscillation has the advantage of being stable.

  FIG. 13 shows the configuration of a laser oscillation apparatus that employs a reproduction mode lock method to modulate the amplitude of laser light. The configuration is the same as that shown in FIG. 2 except that a feedback circuit for electrically extracting the noise of the laser oscillator itself and feeding back the modulation signal to the amplitude modulator is provided.

  This feedback circuit extracts part of the light from the 10% fiber coupler and monitors it with a photodiode (PD1). The electric signal of PD1 is amplified, and the component to be grown is extracted from the super mode noise by a band pass filter (BPF) of 357 MHz ± 7 MHz. The phase is appropriately adjusted by a phase shifter, amplified to an appropriate amplitude by an RF amplifier, and an amplitude modulator provided on the input side of the fiber amplifier is driven.

  Similarly to the configuration of FIG. 2, the optical path length of the optical circuit is the same as the configuration shown in FIG. 2, and an adjustment cable whose length is adjusted is inserted, the fundamental frequency is 6.49 MHz, and the 55th harmonic matches the 357 MHz of the storage resonator. I am doing so.

  Then, the signal of PD1 is divided into two by a splitter so as to monitor the circulating pulse structure, and the signal returned to the amplitude modulator is also divided into two so that the feedback signal can be monitored. By observing these signals with an oscilloscope or spectrum analyzer, the effect of this system can be confirmed.

  In order to confirm the verification of this device, it is assumed that the resonator mirror of the optical resonator uses a resonator mirror with no coating and a reflectivity of 90%. Compare the case where the input cable to the amplitude modulator is removed from the connector and the feedback loop is opened, and the case where the loop is closed.

a) Results with an uncoated resonator mirror FIG. 14 shows the results of measuring the signal of PD1 with a spectrum analyzer when the modulator is off. According to FIG. 14B, super noise peaks are observed at intervals of 6.49 MHz, and FIG. 14A shows that the 55th peak is present in the vicinity of 357 MHz. FIG. 15 shows a monitor signal measured with an oscilloscope. Since noise is composed of a plurality of components, it has a random waveform. In addition, when viewed over a wide span, super mode noise peaks can be observed at intervals of 6.5 MHz.

  FIG. 16 shows the measurement result of the spectrum analyzer for the signal of PD1 when the modulator is on. FIG. 16A and the super noise peak are growing, and FIG. 16B seen in a wide span shows that other peaks are suppressed. The pulse waveform of FIG. 17 obtained by observing PD1 with an oscilloscope shows that a pulse structure is generated in FIG. 17A, and that a stable pulse oscillation is observed even in a long span. ).

b) Result with 90% Reflectance Resonator Mirror FIG. 18 shows the result of measuring the PD1 signal with the spectrum analyzer when the modulator is off. According to FIG. 18 (a), a super noise peak is observed at 357 MHz, and FIG. 18 (b) showing a wide span shows that other peaks are suppressed due to the effect of the resonator. FIG. 19 shows a waveform at this time. Since there are few noise components, the signal after BPF, in particular, shows a waveform of 357 MHz when viewed in a short span in FIG. When observed over a long span of b), the amplitude fluctuates unstablely.

  FIG. 20 shows the measurement result of the spectrum analyzer for the signal of PD1 when the modulator is on, and also shows that the oscillation signal is sharper in FIGS. 20 (a) and 20 (b). FIG. 21 shows waveforms at this time, and both FIG. 21A and FIG. 21B show that pulse oscillation is stable.

  The above measurement results show that according to the device of the present invention, the modulation frequency can be automatically optimized by electrically extracting an appropriate harmonic signal from the oscillation noise peak and using it for amplitude modulation. Show what you can do. Therefore, by electrically extracting an appropriate harmonic signal from the oscillation noise peak and using it for amplitude modulation, the modulation frequency can be automatically optimized and the pulse oscillation can be stabilized.

  As mentioned above, although this invention was demonstrated in relation to the preferred embodiment, this invention is not limited to the said embodiment, In the technical scope, it can implement with a various change or deformation | transformation. Needless to say.

The present invention relates to a laser device that generates strong laser light, and more particularly, to a laser for a light source using laser Compton scattering that can oscillate stably even when the finesse of an optical resonator is increased. In addition, since higher peak intensity can be obtained by introducing amplitude modulation, it has industrial applicability.

Claims (11)

A laser light source that generates laser light for excitation;
A fiber amplifier for generating laser light of a desired wavelength from the laser light;
An optical resonator for resonantly storing the laser light generated by the fiber amplifier;
The fiber amplifier and the optical resonator are formed as an optical circuit for resonating the laser light,
A laser oscillation apparatus, wherein a mode-locked amplitude modulator for amplitude-modulating the laser light is provided on the input side of the fiber amplifier. An optical isolator arranged on the output side of the fiber amplifier, guiding the laser light to one of the optical resonators and blocking laser light in the reverse direction;
The fiber amplifier, the optical resonator and the optical isolator are formed as the optical circuit,
2. The laser according to claim 1, wherein the amplitude modulator is an active mode-locking method in which the laser beam is amplitude-modulated by a modulation signal adjusted to an integer multiple of a frequency corresponding to the optical circuit length. Oscillator. An optical isolator arranged on the output side of the fiber amplifier, guiding the laser light to one of the optical resonators and blocking laser light in the reverse direction;
The fiber amplifier, the optical resonator and the optical isolator are formed as the optical circuit,
2. The reproduction mode lock system in which the amplitude modulator monitors an output of the optical isolator and amplitude-modulates the laser beam by a frequency signal itself of the laser beam that circulates in the optical circuit. The laser oscillation device described in 1. The amplitude modulator comprises:
A photodiode for extracting a part of the laser light from the fiber amplifier;
A first RF amplifier for amplifying the output signal of the photodiode;
A bandpass filter for extracting an RF signal of a desired frequency band to be grown from the output signal of the RF amplifier;
A phase modulator that performs phase modulation of the RF signal that has passed through the bandpass filter;
The laser oscillation apparatus according to claim 3, further comprising: a second RF amplifier that drives the amplitude modulator by an RF signal phase-modulated by the phase modulator.   5. The laser oscillation device according to claim 1, wherein a second fiber amplifier for generating laser light having a desired wavelength from the laser light is disposed on the optical circuit.   6. The laser oscillation device according to claim 1, wherein an adjustment cable for finely adjusting an optical path length of the optical circuit is provided on the optical circuit. The fiber amplifier is
Including the mode-locked amplitude modulator that modulates the light having a desired frequency that is an integral multiple of the frequency corresponding to the optical path length of the optical circuit, and is incident on the laser light generated by the laser light source A first fiber amplifier for emitting the pulse laser beam having the desired frequency;
An adjustment cable corresponding to the wavelength of the pulse laser beam, and a second fiber amplifier that amplifies the pulse laser beam emitted from the optical resonator;
The optical resonator resonantly accumulates the pulsed laser light emitted from the first fiber amplifier;
The laser oscillation device is
A first photodiode for extracting a portion of the laser light from the first fiber amplifier;
A splitter for dividing the output signal of the first photodiode into two;
A first RF amplifier for amplifying one of the two output signals from the splitter;
A bandpass filter for extracting an RF signal of the laser beam having the desired frequency from the output signal of the first RF amplifier;
A phase modulator that performs phase modulation of the RF signal that has passed through the bandpass filter;
A second RF amplifier that drives the amplitude modulator with an RF signal phase modulated by the phase modulator;
A second photodiode for monitoring the other of the two output signals from the splitter;
The pulsed laser light is self-oscillated and amplified and accumulated in the optical resonator by circulating around the optical circuit constituted by the first fiber amplifier, the optical resonator, and the second fiber amplifier,
The laser oscillation apparatus according to claim 1, wherein the adjustment cable is a cable for finely adjusting an optical path length of the optical circuit in the optical circuit.   8. The laser oscillation device according to claim 1, wherein the optical resonator is a Fox Smith interferometer type resonator having at least two concave mirrors facing each other at a predetermined interval. .   9. The laser oscillation according to claim 8, wherein the optical resonator includes a piezo adjuster that finely adjusts a resonator length formed by the two concave mirrors in correspondence with the laser light of the desired wavelength. apparatus.   10. The laser oscillation device according to claim 1, wherein the fiber amplifier is formed of the optical fiber having a core doped with Yb.   11. The laser oscillation apparatus according to claim 1, wherein laser light for a light source using laser Compton scattering is generated.