CN-119362131-B - Full-digital control programmable titanium precious stone femtosecond oscillator carrier envelope offset frequency locking device

CN119362131BCN 119362131 BCN119362131 BCN 119362131BCN-119362131-B

Abstract

The invention discloses a carrier envelope offset frequency locking device of a full-digital-control programmable titanium gemstone femtosecond oscillator, which comprises an avalanche photoelectric detector, a power divider, a first radio frequency conditioning circuit, a second radio frequency conditioning circuit, a frequency discrimination phase discrimination circuit, a programmable proportion circuit, a programmable integration circuit, a programmable bias circuit, an inverse summation circuit, a programmable amplitude limiting circuit, an anti-saturation integration circuit, an output buffer circuit, a main control circuit and an upper computer. The device can lock the carrier envelope offset frequency to the repetition frequency, adopts a programmable PI circuit with all-digital control, combines the innovative functions of anti-saturation integration and output amplitude limiting, and has the advantages of low delay, high precision, high stability and high safety.

Inventors

CHEN SHIWEN
LIANG XINDONG
WU MENGYAO
ZHANG YIWEI
WANG JUNXIANG
JIA JIANJUN

Assignees

国科大杭州高等研究院

Dates

Publication Date: 20260505
Application Date: 20240914
Priority Date: 20240828

Claims (9)

1. An all-digital controlled programmable titanium sapphire femtosecond oscillator carrier envelope offset frequency locking device, comprising: An avalanche photodetector for detecting carrier envelope offset frequency and repetition frequency; the power divider is used for dividing the power of the avalanche photoelectric detection output signal into two paths of output signals; The first radio frequency conditioning circuit is used for filtering and amplifying a first path of output signals of the power divider so as to extract carrier envelope offset frequency; the second radio frequency conditioning circuit is used for filtering, attenuating, dividing frequency and amplifying a second path of output signal of the power divider so as to extract the repetition frequency; The frequency and phase discrimination circuit is used for identifying the phase difference between the repetition frequency and the carrier envelope offset frequency; a programmable proportional circuit for amplifying or attenuating the phase error signal; a programmable integration circuit for filtering and integrating the phase error signal; the programmable bias circuit is used for fine tuning the bias voltage in the output signal of the programmable integration circuit; the inverting summing circuit is used for summing the outputs of the proportional circuit, the integrating circuit and the biasing circuit; the programmable limiting circuit is used for setting an output upper limit voltage and an output lower limit voltage; The anti-saturation integration circuit is used for generating an anti-saturation integration trigger signal and triggering the integration circuit to stop integration when critical saturation occurs; the output buffer circuit is used for isolating an output load and enhancing the load carrying capacity of the circuit; The programmable integrating circuit comprises a fast integrating circuit and a slow integrating circuit, the fast integrating circuit comprises a first integrating circuit, a second integrating circuit and a third integrating circuit, the slow integrating circuit comprises a fourth integrating circuit, the first integrating circuit, the second integrating circuit and the third integrating circuit are connected in series, four groups of integrating capacitors are arranged in the first integrating circuit, the second integrating circuit and the third integrating circuit and used for roughly adjusting unit gain bandwidth, the bandwidth adjusting range of the three groups of integrating circuits is 0.1 Hz-100 KHz, the second integrating circuit and the third integrating circuit can be independently started or stopped, the bandwidth adjusting range of the fourth integrating circuit is 0.001Hz-100 Hz, and the first integrating circuit, the second integrating circuit, the third integrating circuit and the fourth integrating circuit can be independently reset.
2. The all-digital-control programmable titanium-sapphire femtosecond oscillator carrier envelope offset frequency locking device according to claim 1, wherein an output signal of the avalanche photodetector is connected to an input end of the power divider, the power divider equally divides the input signal into two paths and outputs the two paths, and a first path of output is connected to an input end of the first radio frequency conditioning circuit and is used for extracting carrier envelope offset frequency; The output of the first radio frequency conditioning circuit is connected to the input end of the frequency discrimination phase discrimination circuit, the first radio frequency conditioning circuit sequentially comprises a first band-pass filter, a fixed gain amplifying circuit and a first voltage-controlled gain amplifying circuit, the first band-pass filter is used for filtering other frequency components irrelevant to carrier envelope offset frequency, and the fixed gain amplifying circuit and the first voltage-controlled gain amplifying circuit are used for realizing programmable amplification of carrier envelope offset frequency; the output of the second radio frequency conditioning circuit is connected to the input end of the frequency discrimination phase discrimination circuit, the second radio frequency conditioning circuit sequentially comprises a pi-type attenuation circuit, a second band-pass filter, a frequency division circuit, a third band-pass filter and a second voltage-controlled gain amplification circuit, the pi-type attenuation circuit is used for attenuating repeated frequency power and preventing the frequency division device from being damaged due to overlarge input power, the second band-pass filter is used for filtering frequency components irrelevant to the repeated frequency, the frequency division circuit is used for carrying out eight frequency division on the repeated frequency, the third band-pass filter is used for filtering square waves output by the frequency division circuit into sine waves, and the second voltage-controlled gain amplification circuit is used for realizing programmable amplification or attenuation of the repeated frequency.
3. The carrier envelope offset frequency locking device of the all-digital controlled programmable titanium-sapphire femtosecond oscillator is characterized by comprising a digital phase frequency detector and an active loop filter, wherein the phase frequency detector is a voltage type output and has a polarity control function, and the active loop filter is a third-order loop and is used for filtering high-frequency components in output signals.
4. The all-digital-control programmable titanium-sapphire femtosecond oscillator carrier envelope offset frequency locking device according to claim 1, wherein the programmable proportion circuit comprises an instrument amplification circuit, a polarity control circuit, a programmable attenuation circuit and a programmable amplification circuit, the instrument amplification circuit is used for low-noise pre-amplification of a phase error signal, the polarity control circuit is used for changing the positive polarity and the negative polarity of the error signal, and the programmable attenuation circuit and the programmable amplification circuit are used for realizing high-precision attenuation and high-precision amplification of the error signal.
5. The full-digital control programmable titanium gemstone femtosecond oscillator carrier envelope offset frequency locking device according to claim 1, wherein the programmable bias circuit comprises a first bias circuit and a second bias circuit, the bias adjustment ranges are-10 v, and the bias adjustment precision is 0.15mV.
6. The carrier envelope offset frequency locking device of an all-digital controlled programmable titanium-sapphire femtosecond oscillator according to claim 5, wherein the inverting summing circuit comprises a first summing circuit and a second summing circuit, the first summing circuit is used for summing the outputs of the first integrating circuit, the second integrating circuit, the third integrating circuit and the first biasing circuit, the second summing circuit is used for summing the outputs of the fourth integrating circuit and the second biasing circuit, and whether the outputs of the first summing circuit and the second summing circuit participate in the summation can be independently controlled.
7. The full-digital-control programmable titanium gemstone femtosecond oscillator carrier envelope offset frequency locking device according to claim 1, wherein the programmable amplitude limiting circuit comprises a fast integration amplitude limiting circuit and a slow integration amplitude limiting circuit, the fast integration amplitude limiting circuit and the slow integration amplitude limiting circuit both comprise an upper limit amplitude limiting circuit and a lower limit amplitude limiting circuit, the amplitude limiting range of the upper limit amplitude limiting circuit is 0V-10V, the amplitude limiting precision is 0.15mV, the amplitude limiting range of the lower limit amplitude limiting circuit is-10V-0V, and the amplitude limiting precision is 0.15mV.
8. The device for locking carrier envelope offset frequency of a fully digitally controlled programmable titanium sapphire femtosecond oscillator according to claim 1, wherein the anti-saturation integration circuit comprises a first comparator, a second comparator, a third comparator and a multiplexer, wherein the first comparator is used for judging the polarity of a current error signal, the second comparator is used for judging whether the output of the programmable integration circuit reaches an upper limit voltage, the third comparator is used for judging whether the output of the programmable integration circuit reaches a lower limit voltage, and the condition integration strategy of the anti-saturation integration circuit is as follows: When the polarity of the error signal is positive, if the output of the programmable integration circuit reaches the upper limit voltage, triggering the multiplexer to output an anti-saturation signal; when the polarity of the error signal is negative, if the output of the programmable integration circuit reaches the lower limit voltage, triggering the multiplexer to output an anti-saturation signal; When the polarity of the error signal is positive, if the output of the programmable integration circuit reaches the lower limit voltage, the multiplexer is not triggered to output an anti-saturation signal; when the polarity of the error signal is negative, if the output of the programmable integration circuit reaches the upper limit voltage, the multiplexer is not triggered to output an anti-saturation signal; When the programmable integrator circuit output has not reached either the upper or lower voltage limit, the multiplexer is not triggered to output the anti-saturation signal, regardless of the error signal polarity.
9. The carrier envelope offset frequency locking device of the all-digital-control programmable titanium-sapphire femtosecond oscillator according to claim 1, wherein the output buffer circuit comprises a first buffer circuit and a second buffer circuit, the first buffer circuit is used for outputting of a fast integration circuit, the second buffer circuit is used for outputting of a slow integration circuit, and the output circuit is used for isolating a load by adopting an optical coupler.

Description

Full-digital control programmable titanium precious stone femtosecond oscillator carrier envelope offset frequency locking device Technical Field The invention belongs to the technical field of femtosecond lasers in photoelectric information science, and particularly relates to a full-digital control programmable titanium gemstone femtosecond oscillator carrier envelope offset frequency locking device. Background The attosecond laser pulse is one of the most effective tools for researching ultra-fast physical processes, and can be used for carrying out tomography on molecular atoms, capturing hole density evolution after ionization of the atoms and even biological/chemical molecules in real time, and delaying ionization time of electrons in different states on gas molecules, atoms and solid surfaces. The attosecond pulse can not only study the movement of electrons on the outer layer, but also be combined with methods such as X-ray diffraction, electron diffraction and the like, provides an imaging technology with ultra-fast time resolution, is used for researching solid materials, biological materials and the like, and provides a brand-new research means for researching condensed state physics, new materials, ultra-fast chemistry, atomic nucleus physics and the like. The stability of the carrier envelope phase of the titanium sapphire femtosecond oscillator serving as a seed light source of the attosecond beam line plays a crucial role in generating isolated attosecond pulses. The carrier envelope phase (Carrier Envelope Phase, CEP) refers to the phase difference between the optical pulse envelope and the internal electric field peak. When laser pulse passes through medium, the group velocity and phase velocity of pulse are unequal due to dispersion, and the phase difference is generated between carrier peak and envelope peak of light pulse during propagationThe intensity distribution of the electric field in the pulse is affected, and the influence on the periodic magnitude pulse is obvious. When (when)The carrier coincides with the peak of the envelope when 0 or pi, the intensity of the envelope is highest, but whenAt other values, the electric field strength within the envelope decreases. Thus, carrier envelope phase control techniques are very important for titanium-sapphire oscillators to produce stable optical pulse outputs and become a critical technique in producing isolated attosecond pulses. The femtosecond laser pulse sequence is expressed as a comb-shaped longitudinal mode sequence with the oscillator repetition frequency f rep as an interval in a frequency domain, the frequency of the nth longitudinal mode can be expressed as f n＝nfrep+fceo,fceo as a starting point position of the whole comb-shaped spectrum structure, and the frequency is also called as carrier envelope offset frequency, and the carrier envelope offset frequency has the following relation with carrier envelope phase: thus, locking the carrier envelope phase may be achieved by locking the carrier envelope offset frequency. In the generation of isolated attosecond pulses, pulse sequences with the same carrier envelope phase need to be screened out from the optical pulses according to a certain period, and carrier envelope offset frequency needs to be locked to the repetition frequency of one-m times, so that the pulse sequences have the same carrier envelope phase every m pulses. The PI servo controller is the basis for ensuring high-precision locking of carrier envelope offset frequency and repetition frequency, and no integrated frequency locking device capable of directly locking the carrier envelope offset frequency of the titanium sapphire oscillator to one-m repetition frequency exists at present. The laser frequency locking device can be divided into two types of digital and analog, the bandwidth of the digital frequency locking device is generally only tens KHz, and meanwhile, high delay is brought by digital operation, so that the locking time is prolonged, and the locking is difficult, therefore, an analog PI controller is generally adopted for locking carrier envelope offset frequency. The conventional analog PI controller can achieve a bandwidth of several MHz, but P and I parameters are required to be manually adjusted, the adjusting steps are complicated, and high-precision tuning cannot be realized. In addition, the conventional analog PI controller has the problem of integral saturation, the integral saturation can introduce serious overshoot to a control system, and meanwhile, the output amplitude of the common PI controller is uncontrollable, so that the risk of damaging a controlled system exists. Finally, the conventional analog PI controller generally has only 1 integral loop, cannot quickly inhibit high-frequency and low-frequency interference, has poor loop dynamic performance, and can still drift slowly after a controlled system is locked, so that the risk of losing lock exists. Disclosure of Invention In