WO2007073652A1 - Horloge atomique a frequences optiques et faisceau atomique, et son procede de fabrication - Google Patents

Horloge atomique a frequences optiques et faisceau atomique, et son procede de fabrication Download PDF

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Publication number
WO2007073652A1
WO2007073652A1 PCT/CN2006/002501 CN2006002501W WO2007073652A1 WO 2007073652 A1 WO2007073652 A1 WO 2007073652A1 CN 2006002501 W CN2006002501 W CN 2006002501W WO 2007073652 A1 WO2007073652 A1 WO 2007073652A1
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Prior art keywords
atomic
laser
clock
frequency
transition
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PCT/CN2006/002501
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English (en)
French (fr)
Inventor
Jingbiao Chen
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Peking University
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Priority to US12/162,303 priority Critical patent/US8143956B2/en
Priority to GB0817506A priority patent/GB2450270B/en
Publication of WO2007073652A1 publication Critical patent/WO2007073652A1/zh

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    • G—PHYSICS
    • G04—HOROLOGY
    • G04F—TIME-INTERVAL MEASURING
    • G04F5/00—Apparatus for producing preselected time intervals for use as timing standards
    • G04F5/14—Apparatus for producing preselected time intervals for use as timing standards using atomic clocks

Definitions

  • the invention relates to an atomic beam optical frequency atomic clock and a generating method thereof, and belongs to the technical field of optical frequency standard. Background technique
  • the principle of the traditional small-sized calcium atom beam optical frequency standard is: the heating temperature of the calcium furnace is up to 700 degrees Celsius, the hot calcium atom beam is ejected from the calcium furnace, and after collimation, sequentially passes through two parallel and equally spaced pairs of cat eye devices. 657nm laser traveling wave field. Appropriate magnetic fields are added to the Rams ey interaction zone to separate the different magnetic energy levels of the 3P1 state.
  • the conventional small calcium atom beam optical frequency atomic clock is shown in Fig. 1.
  • the purpose of the present invention is to provide an atomic beam optical frequency atomic clock and a method for generating the same for the defects of the existing atomic beam optical frequency atomic clock and its generating device, which can improve the efficiency of atomic detection.
  • the present invention provides a method for generating an atomic beam optical frequency atomic clock, comprising:
  • the atomic beam is ejected from the mouth of the furnace
  • a laser corresponding to the clock transition frequency transfers the particles in the atomic beam from the ground state of the clock transition to the excited state of the clock transition by adiabatic passage;
  • the atomic beam After interacting with the laser corresponding to the clock transition frequency, the atomic beam interacts in the form of a single field or a separate field, and passes through a signal detection region having a detection laser, which detects a laser with a high transition line associated with the atomic clock transition level. Corresponding; after the particles in the atomic beam move to the detection zone and the detection laser, each atom emits spontaneously emitted photons, and the photoelectric receiving system detects the fluorescent photon signals emitted by the detected laser excitation;
  • the modulation method is used to modulate the clock laser that detects the atomic clock transition frequency, and the detected signal is frequency-locked to the clock laser frequency, locked in the atomic clock transition spectrum, and the atomic clock is realized.
  • the detecting laser is at an angle to the atomic beam, adjusting the frequency and line width of the detecting laser, or the divergence angle of the laser, and selecting atoms of a certain velocity group for detection.
  • the atomic beam stream is a different type of atom, molecule or ion.
  • the invention also provides an atomic beam optical frequency atomic clock, comprising:
  • a vacuum chamber having an atomic furnace, a pump laser, a cat's eye path composed of two full mirrors and two lenses perpendicular to the atomic beam;
  • a servo circuit connected to the atomic furnace for controlling the temperature of the atomic furnace
  • the atomic furnace is placed in a vacuum chamber, the temperature of which is controlled by the connected servo circuit; the atomic beam formed by the atomic furnace being heated in the vacuum chamber interacts with the clock laser. Behind this active zone, the atomic beam continues to interact with the detection laser to emit fluorescence; these emitted fluorescence is received by the photodetection device placed in the detection zone and transmitted to the connected servo Road, and feedback to the clock laser through the servo circuit, and finally stabilize the frequency of the clock laser to the frequency corresponding to the atomic clock transition line;
  • the atomic beam is ejected from the atomic furnace, and after collimation, it enters the pumping zone and acts on the pumping light, and then acts as a single-acting or multi-acting zone with the clock-shifting laser.
  • the atom moves to the detection zone and detects the laser, the atom A large amount of fluorescence is detected by the photoelectric receiving system; the detecting laser is a laser corresponding to a strong transition line associated with the atomic clock transition level.
  • the servo circuit is a servo circuit that controls the performance of the atomic clock output frequency.
  • the detection laser and the clock laser are equipped with a frequency automatic control circuit.
  • the vacuum chamber is provided with a small aperture light intercept for collimating the atomic beam.
  • the vacuum chamber has a plurality of light windows for the input and output of the laser.
  • the degree of vacuum in the chamber is greater than 10-2 Torr.
  • the present invention improves the efficiency of atomic detection by utilizing the transform level detection method. That is, the laser corresponding to a strong transition line associated with the atomic clock transition level is used for detection. This ensures that 100% of the atoms that need to be detected can be measured.
  • the detection of the atomic detection of a certain velocity group is performed on the atomic beam type optical frequency atomic clock by using the detection laser beam at an angle with the direction of the atomic beam, thereby improving the signal fringe contrast and increasing the signal-to-noise ratio.
  • the atomic pump is first excited to the excited state of the clock transition, so that a new atomic beam type optical frequency atomic clock based on the atomic excited electromagnetic wave emission process can be realized.
  • FIG. 1 is a schematic structural view of a conventional atom beam type optical frequency atomic clock
  • FIG. 2 is a schematic structural view of a device for generating an atomic beam optical frequency atomic clock according to the present invention
  • FIG. 3 is a schematic diagram showing the energy levels of the calcium atomic optical frequency standard of the atomic beam optical frequency atomic clock generating device of the present invention
  • Fig. 4 is a schematic view showing the probability of the ground state and the excited state of the atomic transition level of the atom at different speeds after passing through the pumping zone in the generating device of the atomic beam optical frequency atomic clock of the present invention.
  • the method for generating an atomic beam optical frequency atomic clock of the present invention comprises the following steps:
  • the atomic beam is ejected from the mouth of the furnace
  • a laser corresponding to the clock transition frequency transfers the particles in the atomic beam from the ground state of the clock transition to the excited state of the clock transition by adiabatic passage;
  • the atomic beam After interacting with the laser corresponding to the clock transition frequency, the atomic beam interacts in the form of a single field or a separate field, and passes through a signal detection region having a detection laser, which detects a laser with a high transition line associated with the atomic clock transition level. Corresponding; after the particles in the atomic beam move to the detection zone and the detection laser, each atom emits spontaneously emitted photons, and the photoelectric receiving system detects the fluorescent photon signals emitted by the detected laser excitation;
  • the modulation method is used to modulate the clock laser that detects the atomic clock transition frequency, and the detected signal is frequency-locked to the clock laser frequency, locked in the atomic clock transition spectrum, and the atomic clock is realized.
  • the calcium atom is taken as an example.
  • the wavelength of 423 allows the laser to excite the clock transition from the ground state atom to the atomic single.
  • the first excited state of the heavy state ⁇ the probability of spontaneous emission of this state is very high, up to 34 million photons per atom per second. This ensures that 100% of each atom that needs to be detected can be measured.
  • the magnesium atom is detected by a 285 nm laser.
  • the atom is pumped to the excited state of the clock transition to realize a new atomic beam type optical frequency atomic clock based on the atomic excited electromagnetic wave emission process.
  • the atomic beam is placed in a vacuum chamber.
  • Atomic beam currents are different kinds of atoms, molecules or ions.
  • the atomic beam optical frequency atomic clock of the present invention includes:
  • a vacuum chamber having an atomic furnace, a pump laser, a cat's eye path composed of two full mirrors and two lenses perpendicular to the atomic beam;
  • a servo circuit connected to the atomic furnace for controlling the temperature of the atomic furnace
  • the atomic furnace is placed in a vacuum chamber whose temperature is controlled by a connected servo circuit; the atomic beam formed by the atomic furnace being heated in the vacuum chamber interacts with the clock laser. Behind this active area, the atomic beam continues to interact with the detection laser to emit fluorescence; these emitted fluorescence is received by the photodetection device placed in the detection zone and transmitted to the connected servo circuit and passed through the servo circuit. Feedback to the clock laser, and finally stabilize the frequency of the clock laser to the frequency corresponding to the atomic clock transition line;
  • the atomic beam is ejected from the atomic furnace, and after collimation, it enters the pumping zone and acts on the pumping light, and then acts as a single-acting or multi-acting zone with the clock-shifting laser.
  • the atom moves to the detection zone and detects the laser, the atom A large amount of fluorescence is detected by the photoelectric receiving system; the detecting laser is a laser corresponding to a strong transition line associated with the atomic clock transition level. It can also be other atoms or molecules, such as magnesium atoms.
  • a beam 423 causes the laser to excite the ground state atoms to the state, and the atoms excited to the 1P1 state emit a photon back to the ground state at an average time of about 5 nanoseconds.
  • each ground state atom can spontaneously emit 5,000 photons.
  • the photodetector in the detection zone can detect any ground state atoms passing through the detection zone.
  • the calcium atom beam is ejected from the furnace to form a ground state. Before entering the action zone, it is first applied with a 657 nm pump laser to adjust the pump laser power to meet the ⁇ pulse transition, so that the atom near the most rapid velocity is pumped. To the 3P1 excited state. Then, in the action zone, the single-acting zone or multiple-acting zone forms a laser with the clock transition 657, and part of the atoms are excited to return to the ground state based on the stimulated radiation process. After the atoms excited to return to the ground state leave the active region, as shown in Fig.
  • a grounded atom of 423 nm is excited by the laser beam in the detection region to the 1 Pi state, which is excited to the state as described above.
  • the atoms will emit a photon back to the ground state at an average time of about 5 nanoseconds, indicating that in the 2 cm detection zone, each ground state atom can spontaneously radiate five thousand photons.
  • the photodetector in the detection zone can detect any ground state atoms passing through the detection zone.
  • the main difference between the structure with or without pre-pumping is that the active region is the difference between atomic stimulated absorption and stimulated emission.
  • the active region is the difference between atomic stimulated absorption and stimulated emission.
  • the spectral line broadening and movement caused by the Doppler effect can be reduced by mechanical slits or small light intercepts and by laser cooling techniques to reduce the lateral velocity distribution of the beam medium.
  • the spectral line broadening and movement caused by the unevenness and fluctuation of the environmental electromagnetic field is reduced.
  • the intensity of the atomic beam is determined by the temperature control of the furnace body, and the signal-to-noise ratio can be adjusted by adjusting the intensity of the particle beam.
  • the laser lock is detected on the fluorescence spectrum of the atomic beam. This fluorescence transmission structure of the laser 5 before the pump laser beam does not affect any performance of the clock.
  • Fig. 2 The structure of the high performance small atomic beam optical frequency atomic clock realized by the present invention is shown in Fig. 2 and described below:
  • the invention mainly comprises a vacuum chamber 2 for maintaining a high vacuum by an ion pump, an atomic furnace 1, a collimating slit 10, a pumping laser 13, a laser full mirror 11, 12, and a control circuit 6.
  • the appropriate position of the vacuum chamber opens the necessary light window for the laser beam 5, 1 3, 14 to pass.
  • the atomic beam 8 is produced by heating the atomic furnace 1.
  • the current of the heating wire and the temperature of the atomic furnace 1 are regulated by the control circuit 6.
  • the clock laser is generated by the laser 4, and 3 is a frequency shifter. 7 is a lens.
  • the signal output of the detector 9 is then controlled by the clock laser 4.
  • 15 is a light blocker.
  • This invention needs to be implemented in the high vacuum chamber 2.
  • the high vacuum in the vacuum chamber is required to be maintained by the ion pump connected to it for a long time.
  • the desired position of the vacuum chamber 2 is opened to provide a desired light window for outputting the input vacuum chamber 2 during laser coupling.
  • a cat's eye path system consisting of the full mirrors 11 and 12, and the lens 7 is placed at an intersection position inside the vacuum chamber 2 perpendicular to the direction of the atom beam 8, and is adjusted by a corresponding fine adjustment mechanism.
  • high vacuum chamber 2 is connected to an ion pump to ensure that the entire high-performance small atomic beam shown in FIG atomic frequency long-term work in high vacuum state, a vacuum better than 10-2 Torr.
  • the length of the vacuum tube can be less than 50 cm.
  • the ion pump has a volume of less than one liter. In short, the volume of the ion to coordinate the vacuum pumping speed to meet the required vacuum better than 10-2 Torr.
  • the flow rate of the atomic beam that we can use is determined, that is, how many atoms are available per unit time.
  • the furnace hole is composed of a long thin tube. Long thin tube length
  • the furnace hole can be composed of a long thin tube array.
  • the atomic beam After the atomic beam is ejected from the high temperature atomic furnace through the furnace hole, it is further collimated, and the aperture can be blocked by a small aperture. Laser beam collimation can also be used to laser collimate the lateral divergence of the atomic beam.
  • the atomic beam then enters the pumping zone and acts with pump light 1 3 .
  • the function of pump light 1 3 is to pump the atoms in the ground state to the excited state.
  • the atomic velocity distribution of the ground state and the excited state after excitation is shown in Fig. 4.
  • the dotted line in the figure is the atomic beam velocity distribution, the solid line with the higher peak value is the excited state atom, and 77% of the atoms are pumped to the excited state, and the peak value
  • the lower solid line is the atom in the ground state, accounting for about 22%. . -
  • the source of the pump light 1 3 can be supplied by a cavity-stable semiconductor laser.
  • the frequency of the pump light 1 3 is locked to the desired atomic spectrum specific value and is implemented by circuit 6.
  • the present invention improves the efficiency of atomic detection by utilizing the transform level detection method.
  • the laser corresponding to a strong transition line related to the clock transition level is used for detection.
  • a laser with a wavelength of 423 faces excites the clock transition in the detection region.
  • the first excited state of the ground state atom to the singlet state of the atom.
  • the probability of spontaneous emission of this state is very high, up to 34 million photons per atom per second. This ensures that 100% of each atom that needs to be detected can be measured.
  • the detection of the atomic detection of a certain velocity group is performed on the atomic beam type optical frequency atomic clock by using the detection laser beam at an angle with the direction of the atomic beam, thereby improving the signal fringe contrast and increasing the signal-to-noise ratio.
  • the atomic pump is first excited to the excited state of the clock transition, so that a new atomic beam type optical frequency atomic clock based on the atomic excited electromagnetic wave emission process can be realized. Due to the great improvement of the signal-to-noise ratio, the calcium beam optical frequency atomic clock realized by the invention will be two orders of magnitude better in stability than the 5 071 small clock, and is an order of magnitude better in accuracy. Therefore, the present invention has the following advantages over all current atom beam type optical frequency atomic clock generating devices and generating methods:
  • the atomic detection efficiency is from 1 ° /.
  • the increase from left to right is about 100%.
  • the atoms of a certain speed group are selected for detection, so that the frequency shift of the atomic clock transition frequency associated with the Doppler effect can be accurately calibrated, thus providing A method for improving the accuracy of an atomic beam type optical frequency atomic clock.

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Description

原子束光频原子钟及其产生方法 技术领域
本发明涉及一种原子束光频原子钟及其产生方法， 属于光频段频率标 准技术领域。 背景技术
传统型小型钙原子束光频标准的原理为：钙炉加热温度到 700摄氏度， 热钙原子束从钙炉中喷射出来， 经过准直后顺次通过平行且等间隔的两对 猫眼装置产生的 657nm激光行波场。在 Rams ey相互作用区加上适当的磁场 以分开 3P1态不同的磁子能级。钙炉出来的 IS O基态原子在 Rams ey相互作 用区受 657nm的 π偏振激光激发， 凡被激发到 3P1态 mF=0子能级的原子会 通过自发辐射跃迁发出 657體荧光。 在原子束流的下游， 用光电检测器来 测量处于激发态的原子自发辐射跃迁发出的 657nm荧光， 传统型小型钙原 子束光频原子钟如图 1所示。
迄今为止所有基于热原子束技术的光频原子钟毫无例外地受限于很 低的荧光信号的信噪比， 从而无法提高稳定性， 最终也限制了可以达到的 准确度。钙原子束光频原子钟目前所能达到的最好准确度略比 5071小铯钟 差，所以不能与 5071小铯钟竟争。其根本原因在于所被利用来检测的 657腿 钟跃迁后原子自发辐射的机率很低， 约一千个光子每秒， 加上检测的有限 荧光收集面积， 使得对原子的检测效率低到仅是 1%左右。 如此之低的原子 的检测效率极大地限制了可以实现的原子钟的准确度和稳定度。 发明内容
本的目的是针对现有原子束光频原子钟及其产生装置的缺陷， 提供一 种原子束光频原子钟及其产生方法， 可以提高原子检测效率。 ' 为实现上述目的， 本发明提供了一种原子束光频原子钟的产生方法， 包括：
真空室内的原子炉加热后从.炉口喷射出原子束；
一与钟跃迁频率对应的激光以绝热通过的方式将上述原子束中的粒子 由钟跃迁的基态转移到钟跃迁的激发态；
原子束在与钟跃迁频率对应的激光以单场形式或分离场的形式相互作 用后， 通过一具有检测激光的信号检测区， 此检测激光的频率与原子钟跃 迁能级相关的一个强跃迁谱线对应； 原子束中的粒子运动到检测区与检测 激光作用后， 每个原子发出自发辐射的光子， 利用光电接受系统探测这些 受检测激光激发而发射的荧光光子信号；
利用调制方法， 对探测原子钟跃迁频率的钟激光进行调制， 由检测到 的信号对钟激光频率进行锁频，锁定在原子的钟跃迁频谱上， 实现原子钟。
所述检测激光与原子束呈一夹角， 调节检测激光的频率和线宽， 或激 光的发散角， 选择一定速度群的原子进行检测。 所述原子束流是不同种类 的原子， 分子或离子。
本发明还提供了一种原子束光频原子钟， 包括：
一真空腔体， 该真空腔体内具有原子炉、 泵浦激光器、 与原子束垂直 的由两个全反镜和两个透镜组成的猫眼光路；
伺服电路， 与所述原子炉相连接， 用来控制原子炉的温度；
检测激光；
钟激光；
光电检测装置；
原子炉置于真空腔体内， 其温度由所连接的伺服电路控制； 原子炉在 真空腔体内被加热后所形成的原子束与钟激光交叉发生相互作用。 在此作 用区的后面， 原子束继续与检测激光交叉发生相互作用而发射荧光； 这些 发射的荧光用置于检测区的光电检测装置所接收而传输到所连接的伺服电 路， 并通过此伺服电路反馈到钟激光， 最后将钟激光的频率稳定到原子的 钟跃迁谱线对应的频率上；
原子束从原子炉喷出， 准直后， 进入泵浦区与泵浦光作用， 然后以单 作用区或多作用区形式与钟跃迁激光作用， 原子运动到检测区与检测激光 作用后， 原子发射大量荧光被光电接受系统探测； 检测激光为与原子钟跃 迁能级相关的一个强跃迁线对应的激光。
所述伺服电路为系统控制原子钟输出频率的性能的伺服电路。 所述检 测激光和钟激光器配备有频率自动控制电路。 所述真空腔体内设有小孔光 拦， 用于准直原子束。 所述真空腔体具有数个光窗， 用于激光的输入和输 出。 所述真空腔室内的真空度大于 1 0— 2乇。
本发明由于利用变换能级检测法， 提高了原子检测效率。 即利用原子 钟跃迁能级相关的一个强跃迁线对应的激光来作检测。 从而保证每个需要 检测的原子 1 00%可以被测量到。 其次， 由于利用了与原子束方向呈夹角的 检测激光束在原子束型光频原子钟上进行选择一定速度群的原子检测的检 测防法， 提高信号条紋对比度从而增加了信噪比。 第三， 由于利用预先泵 浦技术， 先将原子泵浦到钟跃迁的激发态， 从而可以实现基于原子受激电 磁波发射过程的新型原子束型光频原子钟。 附图说明
图 1为现有的原子束型光频原子钟的结构示意图；
图 2为本发明原子束光频原子钟的产生装置的结构示意图；
图 3为本发明原子束光频原子钟的产生装置的钙原子光频标准的能级 示意图；
图 4为本发明原子束光频原子钟的产生装置中， 经过泵浦区后不同速 度原子在钟跃迁能级的基态和激发态的布居机率示意图。
图号说明： 1一原子炉； 2—真空腔体； 3—移频器； 4一钟跃迁激光 （即钟激光， 对钙原子是 657nm ) ; 5—检测激光（对钙原子是 423nm )； 6—系统伺服电 路； 7—猫眼光路结构透镜一和透镜二； 8—粒子束； 9一光电检测器； 10 一光拦准直器； 11 , 12—全反镜； 13—泵浦激光束； 14一钟跃迁激光； 15 一挡光器。
下面结合附图， 对本发明做出详细描述。 具体实施方式
本发明的原子束光频原子钟的产生方法， 包括如下步骤：
真空室内的原子炉加热后从炉口喷射出原子束；
一与钟跃迁频率对应的激光以绝热通过的方式将上述原子束中的粒子 由钟跃迁的基态转移到钟跃迁的激发态；
原子束在与钟跃迁频率对应的激光以单场形式或分离场的形式相互作 用后， 通过一具有检测激光的信号检测区， 此检测激光的频率与原子钟跃 迁能级相关的一个强跃迁谱线对应； 原子束中的粒子运动到检测区与检测 激光作用后， 每个原子发出自发辐射的光子， 利用光电接受系统探测这些 受检测激光激发而发射的荧光光子信号；
利用调制方法， 对探测原子钟跃迁频率的钟激光进行调制， 由检测到 的信号对钟激光频率进行锁频，锁定在原子的钟跃迁频谱上， 实现原子钟。
利用变换能级检测法， 即利用原子钟跃迁能级相关的一个强跃迁线对 应的激光来作检测， 以钙原子为实例是波长为 423讓的激光在检测区激发 钟跃迁的 基态原子到原子单重态的第一激发态 ^， 这个态的原子自发 辐射的几率很高， 高到每个原子每秒辐射三千四百万个光子。 从而保证每 个需要检测的原子 100%可以被测量到。 对镁原子是利用 285nm激光检测。
利用与原子束方向呈夹角的检测激光束在原子束型光频原子钟上进行 选择一定速度群的原子检测的检测方案， 提高信号条紋对比度以增加信噪 比。
利用预先泵浦技术， 先将原子泵浦到钟跃迁的激发态， 实现基于原子 受激电磁波发射过程的新型原子束型光频原子钟。
原子束流置于真空腔室内。原子束流是不同种类的原子、分子或离子。 而本发明的原子束光频原子钟包括：
一真空腔体， 该真空腔体内具有原子炉、 泵浦激光器、 与原子束垂直 的由两个全反镜和两个透镜組成的猫眼光路；
伺服电路， 与所述原子炉相连接， 用来控制原子炉的温度；
检测激光；
钟激光；
光电检测装置；
原子炉置于真空腔体内， 其温度由所连接的伺服电路控制； 原子炉在 真空腔体内被加热后所形成的原子束与钟激光交叉发生相互作用。 在此作 用区的后面， 原子束继续与检测激光交叉发生相互作用而发射荧光； 这些 发射的荧光用置于检测区的光电检测装置所接收而传输到所连接的伺服电 路， 并通过此伺服电路反馈到钟激光， 最后将钟激光的频率稳定到原子的 钟跃迁谱线对应的频率上；
原子束从原子炉喷出， 准直后， 进入泵浦区与泵浦光作用， 然后以单 作用区或多作用区形式与钟跃迁激光作用， 原子运动到检测区与检测激光 作用后， 原子发射大量荧光被光电接受系统探测； 检测激光为与原子钟跃 迁能级相关的一个强跃迁线对应的激光。 也可以是其他原子或分子， 例如镁原子。
钙金属小块被放在炉钟， 被加温到 650摄氏度左右， 钙原子从小细管 中喷射出来形成原子束， 最可几速度约 800米每秒。 先说明没有预先泵浦 的结构。 从炉中喷射出来形成钙原子束处于基态， 然后在作用区以单作用区或 多作用区形式与钟跃迁 657nm激光作用， 部分原子受激发到 ^态， 这些被 激发的原子离开作用区后通过自发辐射的形式发射各向同性的荧光， 但这 种自发辐射率是 400赫兹， 或者说在速度约 800米每秒的原子在平均寿命 期漂移约 20厘米。 传统的方法是检测这种 657nm微弱荧光， 信噪比很低。 在本发明中， 如图 1所示， 在检测区有一束 423讓的激光激发基态原子到 态， 被激发到 1P1态的原子会在平均时间 5纳秒左右发射一个光子回到 基态。 这表示在 2厘米的检测区， 每个基态的原子可以自发辐射五千个光 子。 从而保证在检测区的光电检测器可以检测到任何经过检测区的基态原 子。 通过调制钟跃迁 657nm激光， 被光电接受系统探测到的信号经由检相 器， 滤波器和放大后其输出误差信号把钟跃迁 657nm激光锁定在钙原子的 657腿跃迁谱上， 而最终实现光频钙原子钟。
接着要说明的是有预先泵浦的结构。 从炉中喷射出来形成钙原子束处 于基态， 在进入作用区前先与一束 657nm泵浦激光作用， 调节此泵浦激光 功率以满足 π脉冲跃迁， 使得最可几速度附近的原子被泵浦到 3P1激发态。 然后在作用区以单作用区或多作用区形式与钟跃迁 657讓激光作用， 基于 受激辐射过程部分原子受激后回到基态。 这些被受激回到基态的原子离开 作用区后， 如图 1所示， 在检测区被一束 423nm的激光激发基态原子到 1 Pi 态， 与前面以说明的情形一样， 被激发到 ^态的原子会在平均时间 5纳秒 左右发射一个光子回到基态， 表示在 2厘米的检测区， 每个基态的原子可 以自发辐射五千个光子。 从而保证在检测区的光电检测器可以检测到任何 经过检测区的基态原子。 通过调制钟跃迁 657nm激光， 被光电接受系统探 测到的信号经由检相器， 滤波器和放大后其输出误差信号把钟跃迁 657nm 激光锁定在钙原子的 657nm跃迁谱上， 而最终实现光频钙原子钟。
筒言之， 有无预先泵浦的结构的主要区別是在作用区是原子受激吸收 与受激发射的区別。 频原子钟上进行选择一定速度群的原子检测的检测方案时， 通过调节检测 -激光的频率和线宽， 或激光束的发散角， 来选择一定速度群的原子进行检 测， 从而可以准确标定与多普勒效应相关的原子钟钟跃迁频率的频移。 在 这提供了一种提高原子束型光频原子钟准确度的技术。 原子束方向与检测 激光束之间夹角的大小可以按具体所需进行适当的调节， 以达到最佳的原 子钟性能。
对于粒子束流可以通过机械狭缝或小光拦以及利用激光冷却技术减小 束流介质的横向速度分布来减小多普勒效应引起的谱线加宽和移动。
通过调节外加电磁场的均匀性来减小环境电磁场不均匀和波动引起的 谱线加宽和移动。 原子束流强度由炉体温度控制决定， 可以通过调节粒子 束流强度来调接信噪比。
检测激光锁在原子束的荧光谱上。 这种在泵浦激光束之前的激光器 5 的荧光傳结构不会影响钟的任何性能。
本发明实现的高性能小型原子束光频原子钟的结构， 参见图 2 , 下面 进行描述：
发明主要包括由离子泵维持着高真空的真空腔体 2, 原子炉 1 ,准直缝 1 0 , 泵浦激光 1 3 , 激光全反镜 11、 12 , 控制电路 6。 真空腔体的适当位置 开有必要的光窗一便激光束 5， 1 3 , 14通过。 原子束 8由原子炉 1加热后 产生。 加热丝的电流和原子炉 1的温度由控制电路 6所调节。 钟激光由激 光器 4产生， 3是移频器。 7是透镜。 检测器 9的信号输出后来控制钟激光 器 4。 15为挡光器。
该发明需在高真空腔体 2中实现。 真空腔体中的高真空度长期要求由 其相连的离子泵来维持。 真空腔体 2的适当位置开有所需要的光窗， 以便 激光偶合时输出输入真空腔体 2。 也可在真空腔体内部装置光纤， 由光纤 偶合输出激光。 在高真空腔体有能够产生原子束的原子炉 1。 原子炉的温度决定于所 用的原子， 所需的原子流量等因素。
在真空腔体 2内部与原子束 8方向垂直的交叉位置放置由全反镜 11 和 12 , 以及透镜 7构成的猫眼光路系统， 并由相应的精细调节机械装置来 调节。
高性能小型原子束光频原子钟的结构各部件的连接关系， 功能作用， 和必要要求条件：
高真空腔体 2及其相连的离子泵是用来保证图 1所示的整个高性能小 型原子束光频原子钟能长期工作于高真状态， 真空度优于 1 0— 2乇。
真空管的长度可小于 50厘米。 离子泵的体积小于一升。 总之， 以真空 管体积与离子泵的抽速的协调来满足真空度优于 1 0—2乇的要求。
由原子炉 1的炉体温度和炉口孔的面积来决定我们可利用的原子束的 流量， 即单位时间有多少原子可供利用。 炉孔由长细管构成。 长细管管长
0. 5至 2厘米， 管径 0. 1至 0. 5毫米， 具体据原子束的流量与发散角等要 求而定。 为了加大流量而不至于同时加大发散角， 可由长细管阵列组成炉 孔。
原子束从高温的原子炉经由炉孔喷出来后， 进一步准直， 可用小孔光 拦 1 0。 也可利用激光冷却原理对原子束的横向发散进行激光准直。
参考图 3 , 准直后原子束接着进入泵浦区与泵浦光 1 3作用。 泵浦光 1 3 的功能是将处于基态的原子泵浦到激发态。 激发后基态和激发态原子速度 分布如图 4所示， 图中虛线为原子束速度分布， 峰值较高的实线为激发态 原子， 有 77%的原子被泵浦到激发态， 而峰值较低的实线为处于基态的原 子， 约占 22%。 。 - 泵浦光 1 3的光源可用腔稳的半导体激光器来提供。 泵浦光 1 3的频率 是锁定在需要的原子谱特定值上， 由电路 6实现。
本发明由于利用变换能级检测法， 提高了原子检测效率。 即利用原子 钟跃迁能级相关的一个强跃迁线对应的激光来作检测， 以钙原子为实例是 波长为 423麵的激光在检测区激发钟跃迁的 。基态原子到原子单重态的第 一激发态 ，这个态的原子自发辐射的机率很高， 高到每个原子每秒辐射 三千四百万个光子。 从而保证每个需要检测的原子 1 00%可以被测量到。 其 次， 由于利用了与原子束方向呈夹角的检测激光束在原子束型光频原子钟 上进行选择一定速度群的原子检测的检测防法， 提高信号条纹对比度从而 增加了信噪比。 第三， 由于利用预先泵浦技术， 先将原子泵浦到钟跃迁的 激发态， 从而可以实现基于原子受激电磁波发射过程的新型原子束型光频 原子钟。 由于信噪比的极大提高， 本发明实现的钙束光频原子钟在稳定度 上将比 5 071小铯钟好两个数量级， 在准确度上好一个数量级。 因此， 本发 明与目前所有的原子束型光频原子钟的产生装置和产生方法相比， 具有以 下优点：
一、 将原子检测效率从 1 °/。左右的提高到约 1 00%。
二 、 通过调节检测激光的频率和线宽， 或激光束的发散角， 来选择一 定速度群的原子进行检测， 从而可以准确标定与多普勒效应相关的原子钟 钟跃迁频率的频移， 因此提供了一种提高原子束型光频原子钟准确度的方 法。
三、实现了基于原子受激电磁波发射过程的新型原子束型光频原子钟。 最后， 对于这种高性能小型原子束光频原子钟可能作出并未脱离所附 权利要求书限定的本发明范围的各种变更和改型。 更具体地说， 必须认识 到， 本发明并不限于具体一种原子的一条跃迁谱线， 而适用于任何具有相 似能级结构的原子或分子， 以及离子， 只要这种粒子具有线宽较小可以用 于光频原子钟， 有相关的对应能级可以用本发明中的技术以实现高效率的 检测。
最后应说明的是： 以上实施例仅用以说明本发明的技术方案而非对其进 行限制， 尽管参照较佳实施例对本发明进行了详细的说明， 本领域的普通技 术人员应当理解： 其依然可以对本发明的技术方案进行修改或者等同替换， 而这些修改或者等同替换亦不能使修改后的技术方案脱离本发明技术方案的 ^青神和范围。

Claims

权利要求
1、 一种原子束光频原子钟的产生方法， 其特征在于包括：
真空室内的原子炉加热后从炉口喷射出原子束；
一与钟跃迁频率对应的激光以绝热通过的方式将上述原子束中的粒子 由钟跃迁的基态转移到钟跃迁的激发态；
原子束在与钟跃迁频率对应的激光以单场形式或分离场的形式相互作 用后， 通过一具有检测激光的信号检测区， 此检测激光的频率与原子钟跃 迁能级相关的一个强跃迁谱线对应； 原子束中的粒子运动到检测区与检测 激光作用后， 每个原子发出自发辐射的光子， 利用光电接受系统探测这些 受检测激光激发而发射的荧光光子信号；
利用调制方法， 对探测原子钟跃迁频率的钟激光进行调制， 由检测到 的信号对钟激光频率进行锁频，锁定在原子的钟跃迁频谱上， 实现原子钟。
2、根据权利要求 1所述的原子束光频原子钟的产生方法，其特征在于： 所述检测激光与原子束呈一夹角， 调节检测激光的频率和线宽， 或激光的 发散角， 选择一定速度群的原子进行检测。
3、根据权利要求 1或 2所述的原子束光频原子钟的产生方法， 其特征 在于： 所述原子束流是不同种类的原子， 分子或离子。
4、 一种原子束光频原子钟， 其特征在于包括：
一真空腔体， 该真空腔体内具有原子炉、 泵浦激光器、 与原子束垂直 的由两个全反镜和两个透镜组成的猫眼光路；
伺服电路， 与所述原子炉相连接， 用来控制原子炉的温度；
检测激光；
钟激光；
光电检测装置；
原子炉置于真空腔体内， 其温度由所连接的祠服电路控制； 原子炉在 真空腔体内被加热后所形成的原子束与钟激光交叉发生相互作用。 在此作 用区的后面， 原子束继续与检测激光交叉发生相互作用而发射荧光； 这些 发射的荧光用置于检测区的光电检测装置所接收而传输到所连接的伺服电 路， 并通过此伺服电路反馈到钟激光， 最后将钟激光的频率稳定到原子的 钟跃迁谱线对应的频率上；
原子束从原子炉喷出， 准直后， 进入泵浦区与泵浦光作用， 然后以单 作用区或多作用区形式与钟跃迁激光作用， 原子运动到检测区与检测激光 作用后， 原子发射大量荧光被光电接受系统探测； 检测激光为与原子钟跃 迁能级相关的一个强跃迁线对应的激光。
5、 根据权利要求 4所述的原子束光频原子钟， 其特征在于： 所述伺服 电路为系统控制原子钟输出频率的性能的伺服电路。
6、 根据权利要求 4所述的原子束光频原子钟， 其特征在于： 所述检测 激光和钟激光器配备有频率自动控制电路。
7、根据权利要求 4所述的原子束光频原子钟， 其特征在于： 所述真空 腔体内设有小孔光拦， 用于准直原子束。
8、 根据权利要求 4所述的原子束光频原子钟， 其特征在于： 所述真空 腔体具有数个光窗， 用于激光的输入和输出。
9、 根据权利要求 4所述的原子束光频原子钟， 其特征在于： 所述真空 腔室内的真空度大于 10— 2乇。
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