"Professor Li, what kind of technology are you using, as far as I know, the mold-locking technology used for the test should still be self-locking, right?" Lin Hanwen said in a deep voice.

Everyone set their eyes on Li Kaishan.

Li Kaishan smiled and said: "That's right, in essence, it is still the category of Kerr lens mode locking, and even in the test you just saw, the mode locking technology we used is the technology that was improved by the Institute of Optoelectronics of the Chinese Academy of Sciences two years ago." ”

"This can't be ......" Lin Hanwen immediately vetoed: "According to the principle of mode locking of Kerr lens, after mode locking, if there are 2n+1 longitudinal modes in the cavity, then the peak power of the light intensity resulting from the coherent superposition of so many modes is 2n+1 squared.

In other words, the pulse peak power after clamping will be 2n+1 times that of the unclamped mode.

From the basic formula, it can be easily deduced that the longer the cavity length of the laser, the larger the linewidth value of fluorescence, the greater the number of longitudinal modes, and thus the greater the peak power of the mode-locked pulse.

At this point, two problems arise. ”

Lin Hanwen paused, and continued: "First of all, the problem of pulse peak power, per unit time, the pulse power of this test is as high as 1MW, and when everyone in China is still doing pulse power within 1KW per unit time, you will reach 1MW, which has increased thousands of times, which is incredible."

Secondly, it is the problem of the number of longitudinal modes, not to mention the cavity length, the value is very ordinary, and the cavity length of the resonator we usually use is about the same.

So, the problem comes back to the problem of fluorescence line width.

But as far as I know, it is impossible for all the fluorescent light sources of lasers to have such a large linewidth value as yours. ”

After Lin Hanwen finished speaking, an expert added: "Yes, the line width is directly proportional to the number of laser modes, and the number of modes is the reciprocal of the pulse width under normal circumstances.

Therefore, this pulse width can be approximately regarded as the reciprocal of the fluorescence spectrum width of the laser, or the width of the gain curve, which is inversely proportional to the two.

If you want the pulse width to be narrower, shorter, and smaller, the fluorescence line width must be larger. ”

Lin Hanwen et al. are right, after the advent of mode-locking technology, the minimum pulse duration of a laser pulse can actually be calculated by formula.

Judging from the original results, the laser pulse test conducted by Li Kaishan is not quite in line with the calculation results, so they are very puzzled and questioned.

Li Kaishan was not annoyed when he heard this, but patiently explained: "I understand your feelings and doubts, but the method used by our laboratory to obtain the light source may not be quite the same as what you know, so the fluorescence line width produced is not what you are familiar with. ”

"What's the difference, Professor Li, can you elaborate?" Luo Xianjun hurriedly said.

"Of course. "The related technology has been registered for the patent, and the production technology of this new ultraviolet laser light source will be popularized all over the world in the future.

Therefore, at this time, there is no problem of leaking secrets and revealing to Lin Hanwen and others.

Li Kaishan said: "You should be familiar with the light that believes in the angular momentum of the orbit, and what I am going to talk about next is related to this." ”

"Orbital angular momentum?" the experts looked thoughtful.

But after thinking about it, I still don't know what the relationship between the light of this orbital angular momentum is related to the fluorescence line width.

Li Kaishan: "If two strong infrared laser pulses are emitted into the argon cloud, the gas will be ionized.

And when the ionized electrons violently collide with the argon atoms, the excess energy is released in the form of ultraviolet light with orbital angular momentum.

Everyone should be able to understand this, right?"

Everyone nodded.

Li Kaishan pointed to the big screen, on which some pictures and materials appeared, and continued: "But if the first two infrared laser pulses have different orbital angular momentum, and there are trillions, trillions, or even trillions of a second of async between each other, some wonderful things will happen.

Through our research tests, it was found that a doughnut-shaped pulse of light was formed, just like on a screen.

When the beam is added, the doughnut-shaped pulses of light are superimposed in a strange way, causing the spiral-shaped ultraviolet beam to rapidly accelerate and distort.

They look like a corkscrew, with a gradual change in the rotation of the spiral, resulting in periodic changes in wavelength and frequency, but constant energy and light intensity.

And, if you shine this ultraviolet laser on a flat surface, you will find that it turns from a doughnut into a waning moon. ”

Hearing this, everyone was confused.

"Professor Li, is there any correlation between this line width?"

Li Kaishan said with a smile: "Of course, there is a connection, the line width of this light is no longer the two-dimensional shape of the Gaussian function, but will be three-dimensional in the time domain, and it is periodic.

Therefore, when passing through the resonator, the number of longitudinal modes becomes very large, even if it is only 1 cm in length, and millions of longitudinal modes can be coupled together to produce optical pulses as short as 500 aseconds.

In addition to this, it has a self-torque ......"

In fact, the reason why the self-torque infrared of the black bone health bracelet can form a unique and huge radio wave differential database after reflection is used to target and describe various diseases, is because it is related to the self-torque of this rotating light.

This is a completely new and milestone new light feature that can revolutionize optics.

Li Kaishan: "By greatly inputting the frequency and energy of the infrared laser pulse, it is completely possible to produce this kind of rotating light, and then accurately introduce it into the resonator, and through the simple saturable absorber mode-locking technology, the laser pulse below femtosecond can be obtained."

By increasing the cavity length of the resonator, you can also get more longitudinal mode modes, and in this case, through the stimulated radiation generated by the phase interference between them, you can obtain a UV laser pulse with a shorter pulse duration, such as the 99.6 attosecond pulse you just saw. ”

Why such a short pulse is generated, the principle Li Kaishan has basically explained clearly.

The experts present also understood.

But for a while, the scene was silent, and everyone fell into a silent shock.

After a long time, Lin Hanwen asked in a trembling voice: "Professor Li, the kind of rotating ultraviolet light you are referring to can really produce millions of longitudinal molds in a 1cm chamber alone?"

Unconsciously, when Lin Hanwen called Li Kaishan, he had already used the honorific title of 'you'.

"Of course, if you don't believe it, you can go back and try it yourself, if I Li Kaishan lies, you can insult me as much as you want. Li Kaishan smiled confidently.

"I believe it!" Lin Hanwen added: "It's just that the output power of 1MW needs to be ionized with a high-energy infrared laser pulse to hit the argon atoms, and this process is very difficult to control accurately, and it will cause the equipment to explode if you are not careful, which is too dangerous."

And then you have to introduce the newly generated rotating UV beam into the resonator, and the chance of error in this process is too great, how do you use to avoid the error?"

......