CN104518418A - High-power 671 nm laser obtaining method - Google Patents

Abstract

The invention relates to a high-power 671 nm laser obtaining method, and belongs to the technical field of laser application. The method comprises the following steps: carrying injection locking on seed laser with weak power into a high-power laser diode with a normal temperature wavelength of 658 nm, and using a threshold value adjusting method to find the optimal injection points, so as to achieve the purpose of obtaining 220 mW single mode laser with the wavelength of 670.98 nm. The high-power 671 nm laser obtaining method disclosed by the invention is high in operability; the obtained lithium atom cooled laser is good in single mode performance and high in power.

Description

A method of obtaining high-power 671nm laser

technical field

The invention relates to proposing a high-power 671nm laser acquisition method, which belongs to the technical field of laser applications.

Background technique

In recent years, how to obtain high-power lithium D-line resonance laser has attracted much attention in the cold atom experiment of lithium and the study of quantum degenerate gases. The wavelength of the laser in air is 670.98nm, which requires good single-mode performance. The current acquisition scheme is either expensive or has low output power.

Currently limited by the influence of semiconductor doping materials and processes, the optical power of semiconductor lasers with a wavelength of 671nm is not high, only within 50mW, and external cavity frequency-stabilized lasers made with such laser tubes can often only work below 10mW , far below the power required by cold atom experiments.

Since the Bose Einstein condensate of lithium was realized at Rice University in 1995, lithium has gradually become a new favorite in the field of cold atoms. Lithium has two major advantages for atomic cooling. One is that it has a very simple energy level structure, which contains cyclic transition levels, and the other is that it has a strong coupling effect with electromagnetic fields. These two advantages determine that lithium is very suitable for the application of laser cooling technology. The natural abundance of lithium consists of two isotopes 6Li and 7Li. 6Li is a fermion, and 7Li is a boson, so that two kinds of quantum statistical physics can be studied with lithium. For these two isotopes, we can conveniently apply the Feshbach resonance to tune their s-wave scattering lengths. Lithium's wide resonance point and very low mass are properties that are favored in ultracold atom experiments.

In order to obtain larger samples of cold atoms, magneto-optical trap technology is often used to pre-cool the atoms. In order to optimize the magneto-optical trap, the general practice is to fix the intensity of the cooling laser near the saturation intensity, and then increase the laser power as much as possible to increase the radius of the laser. As the radius of the cooling laser increases, the loading rate increases. Another factor is that the laser spatial mode requires good single mode. The D-line resonant laser of lithium is the cooling laser used in cooling lithium atoms. Its acquisition is currently limited to two ways: dye lasers and external cavity frequency-stabilized lasers. The advantage of dye lasers is that they can output monochromatic light in the order of watts. Its disadvantages are that maintenance is cumbersome, inherently noisy, and requires expensive pump lasers. In order to obtain good spatial mode quality, the characteristic output power of the external cavity frequency stabilized laser is limited within 50mW. Therefore, follow-up laser amplification measures are needed to increase the laser power. The two amplification methods used are tapered amplifiers and laser injection locking. The former approach is to couple the seed laser with a good output mode of the external cavity frequency-stabilized laser to the tapered amplifier. The photons are avalanche-amplified in the tapered cavity, and the output power can reach 500mW. , it is easy to burn out the tapered amplifier. The latter approach is similar, but the current approach is limited by the selection of the laser tube and the adjustment technology of injection locking, so the laser power obtained is low, only about 80mW, and using it as the cooling light of the magneto-optical trap limits the The mass of a cold atomic sample. Recently, another solution has appeared, which adopts the method of all-solid-state laser source to double the frequency of 1342nm laser to obtain a laser with high power output of 671nm. However, this solution is technically difficult and is not conducive to popularization.

Contents of the invention

The purpose of the present invention is to overcome the disadvantages of high cost and high technical difficulty in obtaining 220mW lithium atom cooling laser, and propose a method for obtaining high-power 671nm laser. In this method, a low-power seed laser is injected into a high-power laser diode with a wavelength of 658nm at room temperature to achieve the purpose of obtaining a 220mW 670.98nm single-mode laser.

The present invention is realized by following technology:

Step 1: Use a laser tube with a wavelength of 658nm±1nm at room temperature (25°C) and a power of more than 300mW as the second-level slave laser, and use a laser with a wavelength of 675nm at room temperature as the first-level slave laser.

Step 2: Select the laser generated by the 670nm external cavity laser as the seed laser, and adjust the seed laser to a single-module 670.98nm output with a power of 1.4mW by adjusting the current, temperature and the length of the external cavity. Use the threshold adjustment method to inject the seed laser into the first-stage slave laser at the best injection point.

The concrete method of described threshold adjustment method is:

Step 2.1, adjust the temperature of the first-stage slave laser to about 5°C, so that the first-stage slave laser outputs at the threshold value, and monitor the optical power of the first-stage slave laser with an optical power meter;

Step 2.2, after the first-level slave laser passes through the isolation and coupling optical path, use two mirrors to couple the seed laser into the first-level slave laser;

Step 2.3, repeatedly adjusting the two mirrors used to couple the seed laser into the first slave laser, so that the reading in the optical power meter reaches the maximum;

Step 2.4, then reduce the operating current of the first-stage slave laser, repeat steps 2.2-2.3 until the maximum reading of the optical power meter reaches 3 times that of when the seed laser is not injected, and take the injection locking state at this time as the best Inject the lock point.

The premise of the threshold method adjustment is that the difference between the wavelength of the first-stage slave laser at the threshold and the wavelength of the seed laser is no more than about 4 nm.

Step 3: The second-stage slave laser outputs the second-stage slave laser at the threshold value, and uses a temperature controller to stabilize the temperature of the second-stage slave laser at 70 degrees, so that the wavelength of the second-stage slave laser increases by 10nm.

Step 4: After the second-stage slave laser is isolated and coupled to the optical path, inject the first-stage slave laser obtained in step 2 after injecting the seed laser into the second-stage slave laser, and use the threshold adjustment method to adjust until the best injection is found. lock point.

Step 4.1, after the second-level slave laser passes through the isolation and coupling optical path, use two mirrors to couple the first-level laser into the second-level slave laser; use an optical power meter to monitor the optical power of the second-level slave laser;

In step 4.2, inject the second-stage slave laser through the Fabry-Perot cavity (FP cavity) after injecting the first-stage slave laser, and observe the spectral lines of the second-stage slave laser;

Step 4.3, repeatedly adjusting the two reflectors used to inject the first-stage slave laser into the second-stage slave laser, so that the reading in the optical power meter reaches the maximum;

Step 4.4, then lower the temperature of the second-stage slave laser to 40 degrees, increase the operating current of the second-stage slave laser, and make the second-stage slave laser form a smooth curve from the bottom of the laser line by observing the signal in the FP cavity. The injection locking status of is used as the optimal injection locking point. At this time, the second-level slave laser is a 220mW 670.98nm single-mode laser.

Beneficial effect

The method of the invention has strong operability, and the obtained lithium atom cooling laser has good single-mode property and high power.

Description of drawings

Fig. 1 is a flow chart of the inventive method;

Fig. 2 is the optical path diagram of the 671nm two-stage laser injection locking device in the specific embodiment;

Reference numerals: 1a-first photodiode, 1b-second photodiode, 1c-third photodiode, 2-FP cavity, 3a-first optical isolator, 3b-second optical isolator, 3c-third optical Isolator, 4a-first polarizing beam splitter, 4b-second polarizing beam splitter, 4c-third polarizing beam splitter, 4d-fourth polarizing beam splitter, 5a-first mirror, 5b-second Mirror, 5c-third mirror, 5d-fourth mirror, 5e-fifth mirror, 5f-sixth mirror, 5g-seventh mirror, 5h-eighth mirror, 5i-ninth mirror Mirror, 5j-the tenth reflective mirror, 6a-the first cylindrical mirror, 6b-the second cylindrical mirror, 6c-the third cylindrical mirror, 6d-the fourth cylindrical mirror, 6e-the fifth cylindrical mirror, 6f - sixth cylindrical mirror, 7a - first λ/2 filter, 7b - second λ/2 filter, 7c - third λ/2 filter, 7d - fourth λ/2 filter, 7e - first Fifth λ/2 filter, 7f-sixth λ/2 filter, 7g-seventh λ/2 filter,

Detailed ways

The invention proposes a high-power laser diode with a wavelength of 658nm at normal temperature injected into a low-power seed laser to obtain a 220mW 670.98nm single-mode laser.

The specific operation process is as follows:

Around 658nm, there are cheap laser tubes up to 300mW. In this embodiment, ML101F27 and LPC826 produced by Mitsubishi Corporation are selected, and the price of both is about 45 yuan.

Select ML101F27 and LPC826 laser tubes with long wavelengths at room temperature, and the wavelengths of the emitted lasers at 22°C are 658.6nm and 657.6nm respectively. The main laser is a 670nm external cavity laser produced by TOPTICA, with a maximum output power of 2mW. Through the adjustment of the current, temperature and the length of the external cavity, the main laser is adjusted to a single-module 670.98nm output with a power of 1.4mW. Since the power of the main laser is only 1/200 of the power of the slave laser, which is far lower than the requirement of injection locking, a two-stage injection locking scheme is chosen: first inject a 675nm slave laser with a maximum output power of 15mW with the master laser, and then use the first stage Inject from the laser to lock the second stage from the laser.

The current output of the two current sources in the laser controller can reach 650mA, and the accuracy is below 1μA. The temperature control range of the temperature controller is 10°C to 75°C. The difficulty of this injection locking lies in how to adjust the optical path so that the seed light matches the mode of the slave laser. To adjust the threshold, the specific method is: first adjust the slave laser to the vicinity of the threshold output, inject the seed light, and after isolating and coupling the optical path, use a power meter to monitor the optical power of the slave laser. At this time, the adjustment is used to couple the seed light into the slave The two reflectors of the laser are adjusted repeatedly to maximize the reading in the optical power meter, then further reduce the working current from the laser, and repeat the previous operation until the maximum reading of the optical power meter is about 3 times that of when no seed light is injected. After the threshold adjustment method, it can be considered that the seed light matches well with the mode of the slave laser, and then increase the current of the slave laser, and by observing the signal in the FP cavity, the best injection locking point can be easily found. The premise of the threshold method adjustment is that the difference between the wavelength of the slave laser at the threshold and the wavelength of the seed light does not exceed about 4nm, otherwise the power signal will not increase because the wavelength exceeds the injection range, and the first-stage slave laser injection locking can easily pass the threshold method accomplish. Since the wavelength difference between the second-stage slave laser and the seed light is 13nm, if you want to use the threshold method, you must first increase the slave laser wavelength: use a temperature controller to stabilize the temperature of the second-stage slave laser tube at about 70 degrees, increase the slave laser wavelength Larger than 10nm, then use the threshold adjustment method to make the first-stage slave laser and slave laser mode match and overlap well, then lower the temperature of the second-stage slave laser tube to 40 degrees, increase the operating current, and find the injection locking point. If the injection point cannot be found by increasing the current, increase the temperature slightly until a good injection locking point is found.

This embodiment proposes a 671nm two-stage laser injection locking device, including a wavelength meter a, an oscilloscope, a first slave laser, a second slave laser, a master laser, a wavelength meter b, a first photodiode, a second photodiode, a third Photodiode, FP cavity, first optical isolator, second optical isolator, third optical isolator, first polarizing beam splitter, second polarizing beam splitter, third polarizing beam splitter, fourth polarizing beam splitting , ten identical mirrors, six identical cylindrical mirrors, and eight identical λ/2 filters.

The connection relationship is: the wavelength meter a is connected to the first photodiode; the oscilloscope is connected to the second photodiode, and the optical path of the second photodiode passes through the central axis of the FP cavity, the first polarization beam splitter, and reaches the second reflection mirror; directly above the first polarizing beam splitter is the first mirror, and directly below is the first λ/2 filter; the center of the first mirror is on a straight line with the wavelength meter a and the first photodiode; the first The right side of the polarization beam splitter is the second mirror, and the third mirror is directly below the second mirror; the second polarization beam splitter is directly below the first λ/2 filter, and the second polarization beam splitter The center of the polarizing beam splitter is directly to the left of the third reflector; directly below the second polarizing beam splitter is the third λ/2 filter; on the right left of the polarizing beam splitter are the second λ/2 filter, the An optical isolator, a second cylindrical lens, a first cylindrical lens, and a second-stage slave laser; the fourth reflector is directly below the third λ/2 filter, and the fifth reflector is directly to the right of the fourth reflector mirror, the sixth mirror is directly below the fifth mirror, and the third polarizing beam splitter is directly to the left of the sixth mirror; the fourth λ/2 filter is in turn to the direct left of the third polarizing beam splitter , the second optical isolator, the fourth cylindrical lens, the third cylindrical lens, the first slave laser optical device; the fifth λ/2 filter is directly below the third polarizing beam splitter, and the fifth λ/2 filter The seventh reflector is directly below the sheet, the eighth reflector is directly to the right of the seventh reflector, the ninth reflector is directly below the eighth reflector, and the fourth polarizing beam splitter is directly to the left of the ninth reflector ; The left side of the fourth polarizing beam splitter is the sixth λ/2 filter, the third optical isolator, the sixth cylindrical mirror, the fifth cylindrical mirror, and the seed laser; the fourth polarizing beam splitter Directly below is the seventh λ/2 filter, directly below the seventh λ/2 filter is the tenth reflective mirror, directly to the left of the tenth reflective mirror is the third photodiode, and the third photodiode is connected to the wavelength meter b.

The optical path and working process of the 671nm two-stage laser injection locking device are as follows: the seed laser adopts the laser generated by the 670nm external cavity laser produced by TOPTICA Company, the seed laser is adjusted to a single module 670.98nm output, the power is 1.4mW, and the seed laser passes through the focal length respectively The fifth cylindrical mirror and the sixth cylindrical mirror are 150mm and 50mm, and then pass through the third optical isolator, the seventh λ/2 filter, the fourth polarizing beam splitter, the ninth mirror, and the eighth mirror , The seventh mirror and the first-stage slave laser are injection-locked; the first-stage slave laser passes through the cylindrical mirror, optical isolator and filter in the same way to reach the third polarization beam splitter; the first-stage laser passes through the reflection The mirror reaches the second polarization beam splitter, and then passes through the optical isolator, injects and locks the second-stage slave laser, makes the generated light pass through the FP cavity and wavelength meter a, and observes, when it is found that the spectral line of the second-stage slave laser is absorbed If it is combined with the spectral line of the seed laser, and the bottom is smooth, the injection locking of the second-stage slave laser is completed. At this time, the wavelength of the seed laser is displayed in the wavelength meter, and finally a 670.98nm single-mode laser with 220mW is obtained.

Claims (2)

1. A high-power 671nm laser acquisition method, characterized in that: specifically comprises the following steps: Step 1: Use a laser tube with a wavelength of 658nm ± 1nm at room temperature and a power of more than 300mW as the second-level slave laser, and use a laser with a wavelength of 675nm at room temperature as the first-level slave laser; Step 2: Select the laser generated by the 670nm external cavity laser as the seed laser, and adjust the seed laser to a single module 670.98nm output with a power of 1.4mW by adjusting the current, temperature and the length of the external cavity; The laser is injected into the first stage slave laser at the best injection point; The concrete method of described threshold adjustment method is: Step 2.1, adjust the temperature of the first-stage slave laser to 5°C, so that the first-stage slave laser outputs at the threshold value, and monitor the optical power of the first-stage slave laser with an optical power meter; Step 2.2, after the first-level slave laser passes through the isolation and coupling optical path, use two mirrors to couple the seed laser into the first-level slave laser; Step 2.3, repeatedly adjusting the two mirrors used to couple the seed laser into the first slave laser, so that the reading in the optical power meter reaches the maximum; Step 2.4, then reduce the operating current of the first-stage slave laser, repeat steps 2.2-2.3 until the maximum reading of the optical power meter reaches 3 times that of when the seed laser is not injected, and take the injection locking state at this time as the best injection lock point; Step 3, the second-stage slave laser outputs the second-stage slave laser at the threshold value, and uses a temperature controller to stabilize the temperature of the second-stage slave laser at 70 degrees, so that the wavelength of the second-stage slave laser increases by 10nm; Step 4: After the second-stage slave laser is isolated and coupled to the optical path, inject the first-stage slave laser obtained in step 2 after injecting the seed laser into the second-stage slave laser, and use the threshold adjustment method to adjust until the best injection is found. lock point; Step 4.1, after the second-level slave laser passes through the isolation and coupling optical path, use two mirrors to couple the first-level laser into the second-level slave laser; use an optical power meter to monitor the optical power of the second-level slave laser; In step 4.2, inject the second-stage slave laser through the Fabry-Perot cavity after injecting the first-stage slave laser, and observe the spectral lines of the second-stage slave laser; Step 4.3, repeatedly adjusting the two reflectors used to inject the first-stage slave laser into the second-stage slave laser, so that the reading in the optical power meter reaches the maximum; Step 4.4, then lower the temperature of the second-stage slave laser to 40 degrees, increase the operating current of the second-stage slave laser, and observe the signal in the Fabry-Perot cavity to form the second-stage slave laser line bottom The smooth curve takes the injection-locked state at this moment as the best injection-locked point; the second-level slave laser obtained at this time is a 220mW 670.98nm single-mode laser. 2. A high-power 671nm laser acquisition method according to claim 1, characterized in that: the premise of the threshold method adjustment is that the difference between the wavelength of the first-stage slave laser at the threshold and the wavelength of the seed laser is less than or equal to 4nm.