Chapter 878: Using Light as a Sword

Looking at the titles on the curtain, everyone present highlighted the joys of some families and the sorrows of others.

Whether it is a pulse laser or a continuous laser, it can be said that Chang Haonan has firmly set it up.

Especially for Academician Hou, it felt like he punched nothing and then dodged his waist.

Fortunately, although the process was a bit tortuous, the results are still relatively optimistic.

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

The physical preparation was not in vain, which is always a good thing.

Hou Xun took a few deep breaths and tried to calm down.

The face that had just flushed gradually returned to normal.

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

They were in the opposite situation to Hou Xun. They originally came to the capital with great expectations, but in the end they were disappointed.

But I couldn’t say anything——

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

Moreover, they actually never said what specific technical route they would pursue.

It's just that the Nature article that Chang Haonan published before was indeed very influential, so the people who were sent here speculated that he would continue to work on continuous lasers along the lines of the paper in accordance with academic conventions.

Unauthorized expectation and unauthorized breach of defense are considered appropriate.

However, breaking defense is breaking defense.

To say that there is such a violent reaction to this...

That's not the case.

First of all, Chang Haonan, who is in charge of the project, and Academician Hou Xun, who has the most influence on the scene, have reached an agreement. No matter what the reasons are, others do not have the confidence to oppose 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, the research on this by other units has basically stayed at a superficial level, and the time, energy and money invested are limited.

The sunk costs are not high.

So at most it feels a bit pity.

There will be no frustration like Hou Xun had before when "the work he has been working on for half his life has been denied in principle".

In short, after a small interlude, 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 from the paper you published in Nature..."

The other party hesitated a little.

Obviously, this issue is somewhat sensitive and it is difficult to ask straightforwardly.

If you are not careful, you may be considered to be provoking trouble.

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

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

He answered bluntly:

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

While speaking, he switched to another PPT page.

Shown above are several key figures from the paper.

At this point, Chang Haonan continued:

“In fact, according to our calculations, it is indeed possible to use continuous lasers to perform multi-degree-of-freedom scanning drilling with variable path, beam quality and power to avoid oxidation, stress damage and contour roughness caused by traditional thermal processing. Bad question.”

"It's just that the hardware requirements for lasers are too high. We... let alone us, even developed countries cannot come up with equipment that meets the requirements in a short time. Ultra-short pulse lasers, especially the duration Picosecond or even femtosecond lasers below the lattice relaxation time cannot activate thermal effects in principle, so they are completely cold processing and are more suitable as a key research direction for a developing country. "

When hearing this, the eyes of most people in the venue gradually changed when they looked at Chang Haonan——

You guys in the military industry have really dirty hearts...

Give others a glimmer of light in the wrong direction.

But this glimmer of hope is still real.

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

Just tell me whether you want to follow or not!

As long as there is a little bit of instability in the heart, it will definitely turn into a smile...

Immediately afterwards, Chang Haonan showed several pictures about the calculation process:

"The mechanism of thermal effect machining is relatively clear and is not the focus of our research, so the calculation at the theoretical level is not difficult. I have also demonstrated it in the paper, so I will only give a brief explanation today. The focus is to show you a method The idea of ​​using mathematical methods to guide materials science 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 most likely not understand at least one-third of the content.

That is the part involving mathematical principles.

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

Therefore, Chang Haonan first spent about twenty minutes explaining his results like 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 introduction is to help others build confidence in computational materials science.

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

…

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

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

"Professor Chang, can you tell me specifically what aspects of work we need to be responsible for next?"

"certainly."

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

"Comrades who have been studying ultrashort pulse lasers should be aware that so far, regarding the interaction mechanism between laser and materials, the industry generally still uses the two-temperature equation proposed by Soviet scientists in 1974, that is, The temperatures of the electronic system and the lattice system are represented by the Fourier heat conduction equation, and the two equations are related by the energy transfer term. "

“This equation is simple enough in form, but it can only describe the energy conversion and temperature changes between electrons and crystal lattice, but 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 theoretical 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 provide different corrections for each processing link, and the correction method in turn requires a lot of experiments to obtain, so there is no guidance..."

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

In his past research, he was really troubled by the description error of the two-temperature model.

"So, we need a new model..."

Chang Haonan did not switch the PPT this time, but got up and went to a blackboard placed in the corner of the conference room, and wrote a few big words on it——

Ablation threshold model.

"This is an idea I put forward based on the principles of molecular dynamics. Of course, it is still in a relatively preliminary state."

Chang Haonan wrote another character below.

φ.

“The ablation threshold, I define, is the laser energy flux that is sufficient to destabilize the crystal lattice, cause irreversible damage to the system, and remove at least one layer of material.”

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

“In the process of molecular dynamics calculations, I found that for pulse waves of picosecond or shorter time, the deviation of the ablation threshold is very small, causing ablation to transform 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 material itself and of course the characteristics of the laser source.”

Even people who don't understand the previous mechanical part will see their eyes light up at this time.

"If we only need to consider materials and laser sources, then the complexity of this system... wouldn't it be 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 knowledge of the hardness, stiffness, thermal expansion coefficient, shear strength, etc., of materials and tools in advance, which we collectively refer to as mechanical properties.”

"But ultra-short laser processing is a different set of logic. What we need to do is to find these properties that correspond to mechanical properties and can determine the optical processing effect, and then combine them with the ablation model, and finally achieve the same results as mechanical means. , controllable processing of any known material!”