I just want to be a quiet scholar

Chapter 79

In fact, as early as the early 20th century, physicists noticed that light exerts radiation pressure on atoms. Due to the limitations of instruments and equipment, the laser cooling technology of atoms was not substantially realized until the invention of laser cooling devices in recent decades. develop.

In 1985, Mr. Steven Chu used a three-dimensional laser beam to form a magneto-optical trap to trap atoms in a small area for cooling, and obtained a lower-temperature optical glue in [-].

After more than ten years of painstaking research, Mr. Zhu and his scientific research partners went to the next level. They used this technology to obtain extremely low temperatures below the photon recoil limit.With this achievement, Mr. Zhu, Cohen-Danoke, and Phillips won the Nobel Prize in Physics at the same time in 1997.

After more than 20 years and entering the 21st century, in the laboratory of Nangang No. [-] Middle School, Mr. Mu proposed a question based on the research results of the Nobel Prize in Physics: "In the laser cooling experiment of atoms, considering the recoil effect, What is the minimum temperature that exists?"

The students in the audience scratched their ears and scratched their cheeks: "Mr. Mu, we are only high school students. We won't win the Nobel Prize if we have such a brain hole?"

Only Shen Qi remained silent. He understood what Teacher Mu meant. She didn't expect any high school student to have the level of the Nobel Prize.

This question is about laser emitters and atomic trapping. At first glance, it is very high-end. In the final analysis, the laser cooling experiment of atoms is a verification of the theoretical assumptions of Doppler, de Broglie and others, and it has been promoted and improved gradually.

In high school physics textbooks, high school students learn about the Doppler effect, de Broglie waves, wave-particle duality of light, the Bohr energy level model, alpha particle bombardment, and the basic theory of atomic electrons.Of course, these are some of the hardest parts of high school physics to understand.

Shen Qi has learned big things by himself, and the obstacles to his understanding are relatively small.

As far as problem solving is concerned, if you cannot master the necessary mathematical tools (formulas, deductions, theorems, etc.) Calculate in small amounts.

"It doesn't require a brain hole at the Nobel Prize level. You only need a brain hole at the level of a physics competition." Teacher Mu smiled and asked, "Do you think this problem is difficult?"

"Disaster!"

"IPhO's medium-difficulty test questions, or CPhO's national final theory questions, are almost the same difficulty." Teacher Mu glanced at the next week and said, "You must know that when you participate in the competition, no one will show you a teaching video, you can watch it. Without the 3D demo animation, the only clue is the schematic plan on the roll. Well, it is similar to this plan on the screen. So I played the animation for you, played it twice, and explained it to you synchronously, you shouldn't show it Curious baby's ignorant expression. Future physicists, come up with some real skills, please don't let me down."

The audience was silent for a moment.

The level of the players of the competition team is naturally not too bad, and Shen Qi is not the only one who has taught themselves electives or some knowledge about major things.

All the team members picked up their pens, immersed themselves in writing and drawing on the scratch pad, and deduced calculations.

Shen Qi didn't bring a pen or paper. He came empty-handed, staring at the two-dimensional schematic diagram of the atomic reference frame on the screen, concentrating on something.

"Brother, it's impossible for you to calculate the minimum temperature in your head, right?" Lin Xingyu wrote and found Shen Qi sitting next to him with arms folded.

"Mental arithmetic? It doesn't exist." Shen Qi shook his head and spread out his palm: "Come with a pen."

Lin Xingyu's pencil case contained a bunch of pens, and he took out the most expensive water-based pen and handed it to Shen Qi.

"Paper." Shen Qi spread his palms again.

sizzle.

Lin Xingyu tore a page out of his draft book and handed it to Shen Qi.

Thinking that one page of scratch paper should not be enough, Lin Xingyu tore a few sheets.

"One piece of scratch paper is enough." Shen Qi waved his hand, holding a pen to deduce on the scratch paper.

In the laser cooling experiment of this atom, to calculate the minimum temperature value, the amount of calculation is not large, but the derivation steps are relatively cumbersome. Shen Qi must make a draft, and he must also properly grasp the scale according to the actual situation.

Brush brush.

Shen Qi moved his pen like flying, and quickly filled the front and back of the scratch paper.

"Huh... That's what it is." Shen Qi raised his head and sighed, twisting his neck, he was done.

Teacher Mu noticed Shen Qi: "It seems that Shen Qi has already achieved results?"

Snapped.

Shen Qi snapped his fingers: "Yes."

popping.

Teacher Mu snapped his fingers on his left hand and right hand: "Then ask Shen Qi to show your results."

After cleaning the submarine question on the blackboard, Mr. Mu invited Shen Qi to come on stage to answer.

Shen Qi came to the stage and took a piece of chalk and wrote on the blackboard.

The first step in this problem is to obtain the frequency of the laser, which can be obtained according to the classical Doppler effect:
ω(1+vx/c)

In fact, it is impossible for Doppler himself to realize that the theoretical effect he proposed in a flash of inspiration was widely used in various countries and fields around the world after 200 years.

Today's color Doppler ultrasound in hospitals is based on the Doppler effect, which is also widely used in the military, as well as at the atomic microscopic level.

Shen Qi ordered Doppler to open an exit for the Pioneer Officer. Combined with the topic setting, the Doppler Pioneer Officer entered the enemy camp and made a raid first.

If the electron is coming towards us with a positive velocity v, a backward motion can be obtained, and the lateral size of the entire graph will shrink by the ratio of cv to c.

After taking the second derivative, Shen Qi can calculate an electric field. When the high-energy electrons pass through, they emit radiation in the forward direction. This is Bremsstrahlung. The Doppler pioneer's wave output ends here, and he has completed the order issued by Shen Qi. Task.

Next, it was General De Broglie's turn to go out.

In fact, de Broglie wave has already touched on the preliminary quantum mechanics. The high school physics textbooks are not general, but the essence is written in the textbooks, but there are many conclusive descriptions and few specific explanations.

Shen Qi ordered De Broglie's General Ma Ta to the company's camp. He gave the momentum of an atom absorbing a photon on the blackboard as:
ω0/c
Assuming that the temperature is T, the corresponding de Broglie wavelength is:

λ=/root sign mkT
Wavenumber is the rate of change of phase versus distance, frequency is the rate of change of phase versus time, and ω and k are analogous to time and space in one spatial direction.

Mr. Steven Chu used a three-dimensional laser beam to form a magneto-optical trap to trap atoms in a small space for cooling. The 3D animation played by Mr. Mu just simulated the experimental process. The propagation of light in three-dimensional space interacts with atoms, absorbs The number of atoms after the photon, and the momentum generated by each absorption and radiation of the atom surfaced... Shen Qi filled the blackboard on the left, and the solution process was nearly half completed.

Teacher Mu quietly kept watching. Lin Xingyu, who was under the stage, had the draft that Shen Qi had just typed in front of him.

Lin Xingyu looked down at Shen Qi's draft, and looked up at the solution process on the blackboard. This is not right. Shen Qi's draft is different from what he wrote on the blackboard.

Lin Xingyu could basically understand more than half of the content on the blackboard, but when he looked at Shen Qi's scratch paper, he couldn't understand it at all.

Because what Shen Qi wrote on the scratch paper were relatively independent core steps, and his thinking was so jumpy that few people other than himself could understand what he wanted to express.

Shen Qi took the core steps as the guideline, and started to solve the detailed solution on the blackboard. Soon, the answer will come out soon.

(End of this chapter)