CN-119984762-B - Method for measuring equivalent cavity length of self-injection seed laser

CN119984762BCN 119984762 BCN119984762 BCN 119984762BCN-119984762-B

Abstract

The invention discloses a method for measuring the equivalent cavity length of a self-injection seed laser, which comprises a self-injection seed laser (1) and a balanced homodyne noise detection device (2). The self-injection seed laser self-injection method is characterized in that firstly, intensity noise of the self-injection seed laser is measured by a photoelectric detector in a stable operation state of the self-injection seed laser, relaxation oscillation frequency of the laser in an intensity noise spectrum line is read, then, according to actual parameters of the self-injection seed laser during laser intensity noise measurement, a function graph with the equivalent cavity length of the laser as an independent variable and the relaxation oscillation frequency of the laser as a dependent variable is made by utilizing a theoretical function of the relaxation oscillation frequency of the laser, and finally, the relaxation oscillation frequency value of the laser obtained by measuring in the first step is enabled to be equal to the relaxation oscillation frequency value in a theoretical simulation function graph in the second step, and a value of a corresponding abscissa in the theoretical function graph is read, so that the equivalent cavity length of the self-injection seed laser is obtained. The invention is suitable for measuring the equivalent cavity length of the self-injection seed laser under stable operation.

Inventors

GUO YONGRUI
XU XUESEN
ZHOU XU
ZHANG NANA
Li Renbu

Assignees

重庆邮电大学

Dates

Publication Date: 20260508
Application Date: 20250224

Claims (2)

1. A method of measuring the equivalent cavity length of a self-injection seed laser, comprising the steps of: (1) Measuring intensity noise of laser by using photoelectric detector, and reading relaxation oscillation frequency value of laser from laser intensity noise spectral line ; (2) According to the actual parameters of the laser when measuring the intensity noise of the laser, the theoretical function of the relaxation oscillation frequency of the laser is utilized to make the equivalent cavity length L of the laser as an independent variable and the relaxation oscillation frequency of the laser Graph of function as a dependent variable; (3) Let the relaxation oscillation frequency in the function graph Equal to the relaxation oscillation frequency in the measured intensity noise line Reading in a function graph The corresponding abscissa value is the actual equivalent cavity length of the laser crystal in the running state; the equivalent cavity length L of the laser is taken as an independent variable, and the relaxation oscillation frequency of the laser is taken as the relaxation oscillation frequency In the graph of the function of the dependent variable, Is calculated by using the formula (1): (1); Wherein 2 x Cavity decay rate for laser output mirror coupling mirror, 2 × The cavity decay rate, t, and t, for the laser cavity losses The output coupling mirror transmissivity and intra-cavity linear loss, The equivalent cavity length of the self-injection seed laser resonant cavity is the equivalent cavity length of the self-injection seed laser resonant cavity; (2); Wherein, the Is the stimulated radiation rate of the coupling between the laser crystal atomic transition and the laser cavity mode, sigma s is the stimulated emission section of the laser, For the doping atomic density in the gain medium, For an atomic density corresponding to a doping atomic concentration of 1.0%, For the doping concentration of the gain medium, In order to achieve the light velocity, the light beam is, For the doping length of the laser crystal atoms, Is the refractive index of the laser crystal; (3); Wherein, the In order to be the number of photons in the cavity, For the rate of spontaneous emission at the lower energy level, For the rate of spontaneous emission at the upper energy level, To reverse the fluorescence lifetime of the particles for the upper energy level, For the probability of the ground state particle number distribution, Expressed as: , wherein, For the pumping rate of the pump, Expressed as: , wherein, To measure the pumping power of the laser diode in the corresponding laser when the laser intensity noise is measured, For pump light transmission efficiency, i.e. the ratio of pump light power into the gain medium to pump light power output by the laser diode, , Is the absorption coefficient of the gain medium for the pump laser, In order for the quantum efficiency to be high, In order to output the laser frequency, For the pumping laser frequency, Is a constant of planck, which is set to be the planck's constant, The number of dopant ions utilized in the laser medium is expressed as: , wherein, For pumping the mode volume of the laser at the laser crystal, it is expressed as: , wherein, To pump the beam waist radius of the laser at the center of the laser crystal, Is the wavelength of the pump laser.
2. The method for measuring equivalent cavity length of self-injection seed laser according to claim 1, wherein the laser crystal equivalent cavity length measurement is performed in a self-injection seed all-solid continuous 1064nm continuous laser with four-mirror annular cavity structure, the laser resonant cavity is a butterfly-shaped annular cavity formed by four mirrors, two of which are two plane mirrors, and the other two of which are two curvature radii are Is a plano-concave lens of (c).

Description

Method for measuring equivalent cavity length of self-injection seed laser Technical Field The invention relates to the technical field of laser, in particular to a method for measuring the equivalent cavity length of a self-injection seed laser, which is particularly suitable for measuring the equivalent cavity length of the self-injection seed laser in an actual running state and provides theoretical reference and technical guidance for the preparation of a low-intensity noise laser. Background Self-injection seed lasers are a technique to optimize the output characteristics of the laser by feeding back a portion of its own output light to the resonator as a seed light source. The self-injection seed laser feeds back one arm of the bidirectional output laser path into the laser resonant cavity, so that laser intensity difference is formed between bidirectional lasers, and unidirectional operation of the laser is realized. Compared with a ring laser adopting an optical isolator to realize unidirectional operation, the self-injection end of the self-injection seed laser can compensate noise introduced by loss of the output coupling mirror, and is beneficial to low-intensity noise laser output. Currently, engineering preparation of low-intensity noise self-injection seed lasers still faces technical problems, mainly because the equivalent cavity length of the laser required in preparation of a self-injection seed laser engineering model cannot be determined. The equivalent cavity length of the self-injection seed laser is simultaneously influenced by factors such as the transmissivity of the output coupling mirror of the laser, the optical cavity length of the self-injection feedback end, the reflectivity of the self-injection feedback end reflecting mirror and the like. Currently, the intensity noise of the output laser can only be represented by an intensity noise measurement means under the influence of the composite cavity structure of the self-injection seed laser, so that the preparation of the low-intensity noise self-injection seed laser can only be passively realized by manually changing the parameters of the resonant cavity for a plurality of times and adjusting the resonant cavity for a plurality of times. The actual intensity noise of the self-injection seed laser is not only related to the cavity-shaped structural parameters of the laser, but also influenced by the coherence characteristics of the self-injection feedback laser (related to the transmissivity of the output coupling mirror of the laser, the optical cavity length of the self-injection feedback end and the reflectivity of the self-injection feedback end reflecting mirror). Characterization of the intensity noise of a self-injection seed laser requires measuring the equivalent cavity length of the laser. Meanwhile, engineering preparation of a low-intensity noise self-injection seed laser also requires measuring the equivalent cavity length of the laser. Therefore, the invention develops a measuring method capable of measuring the equivalent cavity length of the self-injection seed laser in the actual running state, and can provide reference for key parameters in engineering preparation of the low-intensity noise self-injection seed laser. CN201010173127.5, an acoustic resonance cavity characteristic length measuring device, which calculates the cavity length by utilizing the change of the diameter of an equal-inclination interference ring of He-Ne and a semiconductor laser and combines multi-wavelength synthesis to expand the range. The method has the defects that the structure of the device is complex, the parallelism of the flat crystals at the two ends of the acoustic resonance cavity is extremely high, and the existing processing technology is difficult to meet. The lack of parallelism can lead to the deformation or blurring of the equal-inclination interference ring, obviously increases the difficulty of image processing, and finally influences the cavity length measurement accuracy. Moreover, the measuring method is only suitable for a straight cavity (F-P cavity structure), greatly increases the measuring difficulty for a laser with an annular cavity structure, and especially has no capability for a self-injection seed laser with a composite annular cavity structure (consisting of an annular cavity and a seed self-feedback section). The method for measuring the equivalent cavity length of the self-injection seed laser is applicable to lasers with straight cavities, standing wave cavities and annular cavity structures, and is particularly applicable to measuring the equivalent cavity length of the self-injection seed laser. Disclosure of Invention The present invention is directed to solving the above problems of the prior art. A method for measuring the equivalent cavity length of a self-injection seed laser is provided. The technical scheme of the invention is as follows: a method of measuring the equivalent cavity length of