Chapter 878: Light as a Sword

Looking at the title on the screen, everyone present felt some were happy while others were sad.

Whether it was pulse laser or continuous laser, it could be said that Chang Haonan had made a solid fool of them.

Academician Hou, in particular, felt as if he had punched in the air and then sprained his waist.

Fortunately, although the process was a bit tortuous, the result is still relatively optimistic.

It doesn't matter if your mental preparation is in vain.

It’s always a good thing that the physical preparation is not in vain.

Hou Xun took a few deep breaths, trying to calm himself down.

The face that had just turned red gradually returned to normal.

Of course, there are also some people whose faces are not so good.

Their situation was the opposite of Hou Xun. They came to the capital with great expectations, but were greatly disappointed in the end.

But I can't say anything -

This project is obviously closely related to military industry, so it is normal to keep it secret before it officially starts.

Moreover, they have never actually said what specific technical route they are going to take.

It’s just that the Nature paper that Chang Haonan published before did have a great influence, so the people who were sent here guessed, according to academic convention, that he would continue to work on continuous lasers along the lines of the paper.

To expect without authorization and to break the defense without authorization is...

However, breaking the defense is still breaking the defense.

To say that there was such a strong reaction to this...

That's not the case.

Firstly, Chang Haonan, who was in charge of the project, and Academician Hou Xun, who had the greatest influence on the scene, had already reached an agreement. No matter what the reasons were, others would not have the confidence to go against these two people at the same time.

Furthermore, as Chang Haonan said before, China's accumulation in laser processing is quite weak.

Except for the Haojing Institute of Optics and Mechanics, other units' research on this issue has basically remained at the superficial level, and the time, energy and money invested are limited.

The sunk costs are not high.

So at most I just feel a little bit regretful.

There will not be the frustration that Hou Xun had before, that "the work I have worked hard for half my life has been denied in principle."

In short, after a small episode, the meeting quickly got back on track.

A researcher from the Institute of Applied Optics hesitated for a moment and then raised his hand:

"Professor Chang, I don't mean anything else...but the data in the paper you published in Nature..."

The other party was a little hesitant.

Obviously, this question is a bit sensitive and it is better not to ask it directly.

If you are not careful, you might be considered as causing trouble.

However, it was not difficult for Chang Haonan to understand the meaning.

"All the data, calculation process, and conclusions are of course true."

He answered bluntly:

"When it comes to academic ethics, our research team is quite strict."

As he spoke, he switched to another page of PPT.

Shown above are some of the key graphs from the paper.

At this point, Chang Haonan continued:

"In fact, according to our calculations, it is indeed possible to circumvent the problems of oxidation, stress damage and poor contour roughness caused by traditional hot working by using continuous laser for multi-degree-of-freedom scanning drilling with variable path, beam quality and power."

"However, the hardware requirements for lasers are too high. We... not to mention us, even developed countries cannot produce equipment that meets the requirements in a short period of time. Ultrashort pulse lasers, especially picosecond or even femtosecond lasers with a duration below the lattice relaxation time, cannot activate thermal effects in principle. Therefore, they are completely cold processing and are more suitable as a key research direction for us as a developing country."

When hearing this, the way most people in the venue looked at Chang Haonan gradually changed -

You military guys have really dirty hearts...

Leave a ray of hope for others in the wrong direction.

But this ray of hope is real.

It seems that you can get it if you work hard.

Just tell me whether you will follow or not!

If you have a little bit of hesitation in your heart, you will definitely catch a black bass...

Then, Chang Haonan showed several pictures of the calculation process:

"The mechanism of thermal effect processing is relatively clear, and it is not the focus of our research, so the theoretical calculation is not difficult. I have demonstrated it in my paper, so today I will only give a brief explanation. The focus is to show you a way of using mathematical methods to guide materials research... I call it computational materials science!"

The paper published by Chang Haonan was not long, but he judged that most researchers in the field of materials science would probably not understand at least one-third of its content.

That is the part that involves mathematical principles.

And this happens to be the core technology that he will use to guide the direction of the project.

Therefore, Chang Haonan spent about twenty minutes explaining his achievements as if he was holding a group meeting.

What is the result...

In fact, I still received a blank look.

But that doesn't matter.

The calculation process itself will be completed by Chang Haonan himself.

The purpose of his presentation this time is to help others build confidence in computational materials science.

Otherwise, if you carry out your work with a skeptical attitude, problems will easily arise.

……

Under the continuous bombardment of theory and reality, the ideas at the symposium were gradually unified.

After Chang Haonan finished the first part of the introduction, Academician Hou spoke first:

"Professor Chang, can you tell us specifically what kind of work we will be responsible for next?"

"of course."

Chang Haonan picked up the cup, took a sip of water, and continued:

"Those who are already studying ultrashort pulse lasers should know that, so far, the industry generally still uses the dual-temperature equation proposed by Soviet scientists in 1974 to study the interaction mechanism between lasers and materials. That is, the temperatures of the electronic system and the lattice system are respectively expressed by the Fourier heat conduction equation, and the two equations are then related by the energy transfer term."

"This equation is simple enough in form, but it can only describe the energy conversion and temperature change between electrons and the lattice, but it cannot explain the statistical laws of microscopic particle motion, nor can it simulate the state of the material after laser processing."

"Even though many scholars have subsequently made parameter corrections based on this model, the shortcomings of the two-temperature model are in principle and cannot be overcome by simply adding fixed terms."

"If you want to use the dual-temperature model to guide industrial production, you need to make different corrections for each processing link, and the correction method in turn requires a lot of experiments to obtain, so there is no guidance at all..."

Not everyone could understand Chang Haonan's introduction to the mechanism, but Academician Hou, who was sitting in the first seat on his left, nodded frequently.

In his past research, he was indeed troubled by the descriptive errors of the two-temperature model.

“So, we need a new model…”

This time, Chang Haonan did not switch the PPT. Instead, he stood up and walked to a blackboard in the corner of the conference room and wrote a few big words on it -

Ablation threshold model.

"This is a concept I proposed based on the principles of molecular dynamics. Of course, it is still in a relatively preliminary stage."

Chang Haonan wrote another character below.

φ。

"I define the ablation threshold as the laser energy flux that is sufficient to destabilize the lattice, irreversibly damage the system, and remove at least one layer of material."

"This threshold does not distinguish between action mechanisms and can be used to describe both cold and hot ablation."

"During the molecular dynamics calculation process, I found that for pulse waves of picoseconds or shorter, the deviation of the ablation threshold is very small, which means that ablation can be transformed from a statistical property to a relatively deterministic behavior. In this way, we eliminate the uncertainty of the processing parameters and only need to consider the characteristics of the processed material itself and, of course, the laser source."

Even those who didn’t understand the previous part of the mechanism would be enlightened at this moment.

"If we only need to consider the material and the laser source, then the complexity of this system...isn't it similar to traditional machining?"

Perhaps due to excitement, Academician Hou's voice was a little distorted.

"exactly."

Chang Haonan turned around and returned to the conference table, but did not sit back in his seat:

"Traditional machining requires knowing the hardness, stiffness, thermal expansion coefficient, shear strength, etc. of the material and tool in advance, which we collectively call mechanical properties."

"But ultrashort laser processing has a different logic. What we need to do is to find the properties that correspond to the mechanical properties and can determine the optical processing effect, and then combine them with the ablation model. Finally, we can achieve controllable processing of any known material just like mechanical means!"