CN105811232B - A kind of adjusting method generating mode excitation optical path for passive optical resonant cavity - Google Patents

Abstract

The present invention provides a kind of adjusting method that mode excitation optical path is generated for passive optical resonant cavity, including builds beam path alignment model step；Beam path alignment step；Optical path coarse steps；Optical path fine tuning step.The more optical elements and adjust view mode that the present invention establishes, have the advantages that adjustment structure and adjustment process are clear, step is clear, judgement is effective, optical resonator can be made to reach best regulating effect.

Description

A method for adjusting the excitation light path of passive optical resonant cavity generation mode

technical field

The invention relates to the technical field of laser light path adjustment, in particular to a method for adjusting the excitation light path of a passive optical resonant cavity generation mode.

Background technique

With the development of laser technology, the design of optical resonant cavity has also appeared in many applications, such as: integrating cavity cavity, cavity enhancement cavity, cavity ring-down cavity and many other types. However, in general, these cavities belong to a kind of passive optical resonant cavity, and the research on its optical properties can be traced back to the 1960s, when Herriott et al. used this method to realize the delay or long optical path of light For absorption spectroscopy measurements, this type of multiple reflection cavity was commonly used in the previous research on Tunable Semiconductor Laser Absorption Spectroscopy (TDLAS).

In principle, the resonant cavity can be regarded as a long-distance Fabry-Perot cavity. However, the adjustment of the resonant cavity is the most critical work in the above-mentioned absorption spectroscopy technology. The fineness of the resonant cavity adjustment has an important impact on the sensitivity of the measurement. Not only does it require a lot of energy, but also enough patience and rich experience.

Contents of the invention

The purpose of the present invention is to provide an adjustment method for the excitation light path of the mode generated by the passive optical resonant cavity, so that the passive optical resonant cavity can achieve the best adjustment effect.

Technical scheme of the present invention is:

A method for adjusting the excitation light path of a passive optical cavity to generate a mode, comprising the following steps:

(1) Steps to build the optical path collimation model, including:

(11) Using He-Ne visible light laser as collimated light source;

(12) A semi-transparent mirror, a first total mirror and a second total mirror are arranged sequentially between the He-Ne visible light laser and the resonator, so that the He-Ne visible light output by the He-Ne visible light laser passes through the semi-transparent The reflection of the half-mirror, the reflection of the first total reflection mirror and the reflection of the second total reflection mirror can be irradiated onto the cavity mirror at the incident end of the resonant cavity;

(2) Optical path collimation steps, including:

(21) Set the first adjustable diaphragm and the second adjustable diaphragm between the half mirror and the first total mirror, and replace the resonant cavity with the third adjustable diaphragm and the fourth adjustable diaphragm respectively The incident end cavity mirror and the transmission end cavity mirror;

(22) Adjust the positions of the He-Ne visible light laser, the half mirror, the first total reflection mirror and the second total reflection mirror, so that the He-Ne visible light output by the He-Ne visible light laser passes through the first adjustable aperture at the same time , the small holes of the second adjustable diaphragm, the third adjustable diaphragm and the fourth adjustable diaphragm;

(3) Coarse optical path adjustment steps, including:

(31) Remove the third adjustable diaphragm and the fourth adjustable diaphragm, reinstall the cavity mirror at the incident end and the cavity mirror at the transmission end of the resonator, and keep the positions of other components unchanged;

(32) Adjust the relative parallelism between the cavity mirror at the incident end and the cavity mirror at the transmission end of the resonator, and observe the interference ring generated by He-Ne visible light on the receiving screen after passing through the resonator, until the fluctuation frequency of the interference ring and the scanning pressure The frequency of the control voltage of the electric ceramic is the same; the piezoelectric ceramic is arranged close to the outside of the cavity mirror at the incident end of the resonant cavity and has the same size as the cavity mirror at the incident end;

(4) Optical path fine-tuning steps, including:

(41) Use a tunable mid-infrared semiconductor laser as the excitation light source, so that the mid-infrared laser output by the tunable mid-infrared semiconductor laser can be transmitted through the half-transparent mirror, reflected by the first total mirror and reflected by the second total mirror in sequence. Irradiate on the cavity mirror at the incident end of the resonant cavity;

(42) Turn off the He-Ne visible light laser, turn on the tunable mid-infrared semiconductor laser, adjust the position of the tunable mid-infrared semiconductor laser, observe the direction of the mid-infrared laser output by the tunable mid-infrared semiconductor laser with a mid-infrared photosensitive plate, and make the mid-infrared semiconductor laser The infrared laser passes through the small holes of the first adjustable aperture and the second adjustable aperture at the same time;

(43) Observe the transmission peak of the resonator displayed on the oscilloscope, and continue to adjust the position of the tunable mid-infrared semiconductor laser to gradually increase the intensity of the transmission peak;

(44) When continuing to adjust the position of the tunable mid-infrared semiconductor laser cannot increase the intensity of the transmission peak, set the matching lens between the first adjustable diaphragm and the second adjustable diaphragm, and adjust the position of the matching lens , so that the intensity of the transmission peak increases gradually.

In the method for adjusting the excitation optical path of the passive optical resonant cavity generation mode, the step of fine-tuning the optical path further includes:

Jointly adjust the position of the tunable mid-infrared semiconductor laser, the position of the matching lens, and the positions of the incident end cavity mirror and the transmission end cavity mirror of the resonator, and observe the intensity change of the transmission peak on the oscilloscope and the number of cavity modes excited by the mid-infrared laser At the same time, the fineness of the resonant cavity is calculated, and the calculated fineness of the resonant cavity is compared with the theoretical fineness of the resonant cavity until the difference between the two is within a certain threshold range.

In the method for adjusting the excitation light path of the passive optical resonant cavity generation mode, the first total reflection mirror and the second total reflection mirror are both 45-degree total reflection mirrors.

The beneficial effects of the present invention are:

It can be seen from the above technical solution that the multi-optical elements and adjustment observation method established by the present invention have the advantages of clear adjustment structure and adjustment process, clear steps, effective judgment, and can make the optical resonant cavity achieve the best adjustment effect.

Description of drawings

Fig. 1 is method flowchart of the present invention;

Fig. 2 is a schematic diagram of the collimated light path of the present invention;

Fig. 3 is a schematic diagram of the coarse adjustment optical path of the present invention;

Fig. 4 is a schematic diagram of the fine adjustment optical path of the present invention.

Detailed ways

As shown in Figure 1, a method for adjusting the excitation light path of a passive optical cavity to generate a mode includes the following steps:

S1. Steps of building an optical path collimation model, including:

S11, using a He-Ne visible light laser as a collimated light source;

S12. Between the He-Ne visible light laser and the resonant cavity, a half mirror, a first total reflection mirror and a second total reflection mirror are sequentially arranged, so that the He-Ne visible light output by the He-Ne visible light laser passes through the semi-transmission and half-mirror sequentially. Mirror reflection, first total reflection mirror reflection and second total reflection mirror reflection can be irradiated onto the cavity mirror at the incident end of the resonant cavity;

Wherein, the reflection wavelength of the half-transparent mirror is 632nm, and the first total reflection mirror and the second total reflection mirror are both 45-degree total reflection mirrors.

S2. The step of collimating the optical path, including:

S21. A first adjustable aperture and a second adjustable aperture are arranged between the half mirror and the first total reflection mirror, and the third adjustable aperture and the fourth adjustable aperture are respectively used to replace the resonant cavity Incident end cavity mirror and transmission end cavity mirror;

S22. Adjust the positions of the He-Ne visible light laser, the half mirror, the first total reflection mirror and the second total reflection mirror, so that the He-Ne visible light output by the He-Ne visible light laser passes through the first adjustable diaphragm, The apertures of the second adjustable diaphragm, the third adjustable diaphragm and the fourth adjustable diaphragm.

S3, the rough adjustment step of the optical path, including:

S31. Remove the third adjustable aperture and the fourth adjustable aperture, reinstall the cavity mirror at the incident end and the cavity mirror at the transmission end of the resonator, and keep the positions of other components unchanged;

S32. Adjust the relative parallelism between the cavity mirror at the incident end of the resonator and the cavity mirror at the transmission end, and observe the interference ring generated after He-Ne visible light on the receiving screen passes through the resonator until the fluctuation frequency of the interference ring is the same as the scanning piezoelectric The frequency of the control voltage of the ceramics is consistent; the piezoelectric ceramics are arranged close to the outside of the cavity mirror at the incident end of the resonant cavity and have the same size as the cavity mirror at the incident end.

S4. Steps for fine-tuning the optical path, including:

S41. Using a tunable mid-infrared semiconductor laser as an excitation light source, so that the mid-infrared laser output by the tunable mid-infrared semiconductor laser can be irradiated after being transmitted through the half-transparent mirror, reflected by the first total mirror and reflected by the second total mirror. to the cavity mirror at the incident end of the resonator;

S42, turn off the He-Ne visible light laser, turn on the tunable mid-infrared semiconductor laser, adjust the position of the tunable mid-infrared semiconductor laser, observe the direction of the mid-infrared laser output by the tunable mid-infrared semiconductor laser with a mid-infrared photosensitive plate, and make the mid-infrared The laser light passes through the small holes of the first adjustable diaphragm and the second adjustable diaphragm at the same time;

S43. Observe the transmission peak of the resonator displayed on the oscilloscope, and continue to adjust the position of the tunable mid-infrared semiconductor laser, so that the intensity of the transmission peak increases gradually;

S44. When continuing to adjust the position of the tunable mid-infrared semiconductor laser cannot increase the intensity of the transmission peak, set the matching lens between the first adjustable diaphragm and the second adjustable diaphragm, and adjust the position of the matching lens, Make the intensity of the transmission peak gradually increase;

S45. Jointly adjust the position of the tunable mid-infrared semiconductor laser, the position of the matching lens, and the positions of the incident end cavity mirror and the transmission end cavity mirror of the resonator, and observe the intensity change of the transmission peak on the oscilloscope and the mid-infrared laser on the cavity mode At the same time, the fineness of the resonant cavity is calculated, and the calculated fineness of the resonant cavity is compared with the theoretical fineness of the resonant cavity until the difference between the two is within a certain threshold range.

Working principle of the present invention:

The correct adjustment of the resonator includes the following meanings: the incident laser only excites the fundamental mode of the resonator, and does not excite any high-order mode, or in other words, the position and size of the beam waist of the incident laser and the beam waist of the resonator should be exactly the same ( That is, the positions of the beam waists of the two coincide and the radii are equal). Therefore, the adjustment process of the resonant cavity is actually a process of selecting a matching lens with a certain focal length, determining the position of the matching lens in the optical path, and coordinating the positional relationship among the light source, matching lens and resonant cavity mirror. In the adjustment of the resonator, to meet the above requirements, the following points need to be done: first, the optical axis of the incident laser and the axis of the resonator should be coaxial; secondly, the positions of the beam waist of the incident laser and the beam waist of the resonator The size should be exactly the same. Otherwise, the excitation of high-order modes of the resonator will inevitably occur in the experimental operation, which will reduce the signal-to-noise ratio of the monitoring.

Since most of the incident laser light output by the mid-infrared laser light source cannot be directly observed by the eyes, the adjustment of the optical path first needs to be carried out with the help of visible light, and the adjustment steps can be roughly divided into rough adjustment and fine adjustment. It cannot be predicted, so it needs to be adjusted timely according to the actual situation.

Coarse adjustment process: During the adjustment process, a He-Ne visible light laser 2 is used as the light source of the collimated optical path, and the collimated optical path is shown in Figure 2. When the optical path is collimated, the two cavity mirrors of the resonator 5 are replaced by two adjustable diaphragms 63 and 64, and the He-Ne visible light laser 2, the half mirror 3 and the two total mirrors 41 are adjusted. , 42, He-Ne visible light passes through the small holes of the four adjustable diaphragms 61, 62, 63, 64 simultaneously. After the optical path is collimated, the resonant cavity 5 is first roughly adjusted with He-Ne visible light: the two cavity mirrors 51 and 52 of the resonant cavity 5 are fixed to the two ends of the resonant cavity 5, and the positions of other parts remain unchanged, such as Figure 3 shows. Adjust the relative parallelism between the two cavity mirrors 51 and 52, and observe the interference ring produced by He-Ne visible light on the receiving screen 8 passing through the resonator 5 and converging through the focusing lens 7 until the He-Ne through the resonator 5 Ne visible light produces an obvious interference ring. At this time, if a periodically changing control voltage is applied to the piezoelectric ceramic (the piezoelectric ceramic is placed close to the outside of the cavity mirror 51 at the incident end of the resonator and has the same size as the cavity mirror 51 at the incident end) , it can be observed that the fluctuating frequency of the interference ring is consistent with the frequency of the control voltage of the scanning piezoelectric ceramic, so far, it can be considered that the rough adjustment of the resonant cavity 5 is completed.

Fine adjustment process: Since He-Ne visible light can be directly observed by eyes, the rough adjustment of the resonant cavity 5 is relatively intuitive. The fine-tuning result can only be judged by the transmission peak displayed on the oscilloscope 10. Since the transmission peak intensity of the resonant cavity 5 is relatively weak, the data of the oscilloscope 10 needs to be averaged many times, so the response lags behind. The fine-tuning work adds a lot of difficulty. The fine-tuning process is as follows:

(1) Turn off the He-Ne visible light laser 2, turn on the tunable mid-infrared semiconductor laser 1, finely adjust the incident direction and position of the mid-infrared laser, observe the direction of the mid-infrared laser with a mid-infrared photosensitive plate, and make the beam pass through the optical path at the same time The small holes of the two adjustable diaphragms 61 and 62 observe the transmission peak signal of the resonant cavity 5 displayed on the oscilloscope 10 after the mid-infrared laser light passes through the resonant cavity 5 and is converged by the focusing lens 7 and detected by the detector 9, as shown in the figure 4.

(2) After observing the transmission peak signal of the resonator 5 on the oscilloscope 10, continue to fine-tune the incident direction and position of the mid-infrared laser. It can be seen that the transmission peak of the resonator 5 becomes regular, and the mode structure gradually appears. Because the incident laser light regularly excites a few cavity modes from the original scattered excitation of multiple modes, the energy of the excitation light gradually concentrates on the few excited cavity modes, so the intensity of the transmission peak of the resonant cavity 5 is gradually strengthened.

(3) If continuing to adjust the position of the incident laser light cannot increase the intensity of the transmission peak, the matching lens 11 should be added to the optical path, and the position of the matching lens 11 should be carefully adjusted to better meet the requirements between the incident laser light and the resonant cavity 5. The mode matching relationship, so that the excitation of the incident laser to the high-order mode of the resonator is further suppressed, so that most of the energy is concentrated on a few individual cavity modes. At this time, the transmission peaks of the resonant cavity 5 are not only more regular, but also stronger.

(4) If further adjustment is required, the position of the tunable mid-infrared semiconductor laser 1, the position of the matching lens 11, and the two cavity mirrors 51 and 52 must be adjusted jointly to finally achieve single-mode excitation of the incident laser to the resonator 5 , so that the transmission peak intensity of the resonant cavity 5 reaches the maximum. This adjustment process not only needs to observe the change of the intensity of the transmission peak and the number of cavity modes excited by the incident laser, but more importantly, it is necessary to continuously calculate the fineness of the resonator 5 by using the relationship F=FSR/FWHM, where FSR represents the free spectrum area, FWHM represents the half-width of the peak value, and is compared with the theoretical fineness of the resonant cavity 5 until the values of the two are relatively close.

The above-mentioned embodiments are only descriptions of the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, those skilled in the art may make various modifications to the technical solutions of the present invention. and improvements, all should fall within the scope of protection determined by the claims of the present invention.

Claims (3)

1. a kind of adjusting method for generating mode excitation optical path for passive optical resonant cavity, which is characterized in that including following step Suddenly：

（1）Beam path alignment model step is built, including：

（11）Using He-Ne visible laser as collimated light source；

（12）It is complete that semi-transparent semi-reflecting lens, the first total reflective mirror and second are set gradually between He-Ne visible laser and resonant cavity Anti- mirror, make He-Ne visible laser export He-Ne visible light successively pass through semi-transparent semi-reflecting lens reflection, the first total reflective mirror it is anti- Penetrating can be irradiated in the incidence end hysteroscope of resonant cavity with after the reflection of the second total reflective mirror；

（2）Beam path alignment step, including：

（21）First adjustable diaphragm and the second adjustable diaphragm are set between semi-transparent semi-reflecting lens and the first total reflective mirror, and can with third Light modulation door screen and the 4th adjustable diaphragm replace the incidence end hysteroscope and transmission end hysteroscope of resonant cavity respectively；

（22）The position for adjusting He-Ne visible laser, semi-transparent semi-reflecting lens, the first total reflective mirror and the second total reflective mirror, makes He-Ne Visible laser output He-Ne visible light simultaneously pass through the first adjustable diaphragm, the second adjustable diaphragm, third adjustable diaphragm and The aperture of 4th adjustable diaphragm；

（3）Optical path coarse steps, including：

（31）Third adjustable diaphragm and the 4th adjustable diaphragm are removed, again by the incidence end hysteroscope of resonant cavity and transmission end hysteroscope It loads onto, the position of other each elements remains unchanged；

（32）The opposite depth of parallelism between the incidence end hysteroscope and transmission end hysteroscope of resonant cavity is adjusted, He-Ne on receiving screen is observed The interference ring generated after visible light-transmissive resonant cavity, until the scan-control voltage of the vibration frequency and piezoelectric ceramics of interference ring Frequency is consistent；It is arranged on the outside of the incidence end hysteroscope of the piezoelectric ceramics abutting resonant cavity and identical as incidence end hysteroscope size；

（4）Optical path fine tuning step, including：

（41）Using tunable middle infrared semiconductor laser as excitation light source, keep tunable middle infrared semiconductor laser defeated Mid-infrared laser out can successively irradiate after semi-transparent semi-reflecting lens transmission, the reflection of the first total reflective mirror and the reflection of the second total reflective mirror Onto the incidence end hysteroscope of resonant cavity；

（42）He-Ne visible laser is closed, tunable middle infrared semiconductor laser is opened, is adjusted infrared by half in tunable The position of conductor laser, infrared photographic plate observes the mid-infrared laser of tunable middle infrared semiconductor laser output in Direction makes mid-infrared laser while passing through the aperture of the first adjustable diaphragm and the second adjustable diaphragm；

（43）The transmission peaks of the resonant cavity shown on observation oscilloscope continue the position for adjusting tunable middle infrared semiconductor laser It sets, gradually increases the intensity of transmission peaks；

（44）When the position for continuing to adjust tunable middle infrared semiconductor laser cannot be such that the intensity of transmission peaks continues growing, Matching lens are arranged between the first adjustable diaphragm and the second adjustable diaphragm, adjusts the position of matching lens, makes transmission peaks Intensity gradually increases.

2. the adjusting method according to claim 1 for generating mode excitation optical path for passive optical resonant cavity, feature It is, the optical path fine tuning step further includes：

To the position of tunable middle infrared semiconductor laser, the position of matching lens and the incidence end hysteroscope of resonant cavity and thoroughly The position for penetrating end hysteroscope carries out joint adjusting, and the Strength Changes of transmission peaks and mid-infrared laser excite cavity mold on observation oscilloscope The number of quantity, while calculating the fineness of resonant cavity, and by the theory of the fineness for the resonant cavity being calculated and resonant cavity Fineness compares, until the difference of the two is in certain threshold range.

3. the adjusting method according to claim 1 for generating mode excitation optical path for passive optical resonant cavity, feature It is, first total reflective mirror and the second total reflective mirror are 45 degree of total reflective mirrors.