We all know that lasers are widely used in daily life, so do you know how lasers emit light? What is the working principle of laser diode? Let's take a look at it together.

In daily life and industrial production, lasers can be seen everywhere: the scanning gun at the checkout counter in the supermarket, the medical equipment in the operating room, the laser cutting machine in the factory, and even our commonly used optical fiber communication are all inseparable from lasers. So the question is, how does the laser shine? How does the laser diode work? Today, we will give you a comprehensive interpretation in simple language.

First, the difference between laser and ordinary light

Everyone knows that light bulbs and LEDs can also emit light, so why do you need a "laser"?

1. Ordinary light (such as LED)

The light is messy and divergent in all directions;

Mixed colors, wide wavelength;

Not suitable for long-distance transmission and high-precision machining.

2. Laser

Good monochromaticity: almost a single wavelength, it looks like a kind of "pure light";

Strong directivity: the beam divergence is very small and can spread far;

Good coherence: the fluctuation of light is "uniform" and the energy is concentrated;

High brightness: the energy density per unit area is much higher than that of ordinary light.

This is why laser can be used for precision measurement, information transmission and high-energy processing.

Second, how does the laser shine?

The core principle of laser has three key processes:

1. stimulated radiation

When excited by external energy, atoms or electrons will jump to high energy levels;

When the high-energy electron falls back to the low-energy state, it will release a photon;

If you happen to meet another photon with the same frequency, you will be "stimulated" to release a photon exactly the same as it;

The two photons continue to "copy", thus forming light with the same direction, frequency and phase.

2. The number of particles is reversed

In order to make stimulated radiation continue to occur, it is necessary to make more electrons in high energy state than in low energy state;

This process is called "population inversion", which is a necessary condition for generating laser.

3. Optical resonator

Reflecting back and forth between two mirrors, the number of photons is constantly amplified;

One of the mirrors is partially transparent, and the light that finally "leaks" is the laser we see.

Third, the working principle of laser diode

So, how does Laser Diode, LD) turn these physical principles into reality?

1. Basic structure

Laser diode is a special semiconductor device, which consists of P-type semiconductor and N-type semiconductor.

An active layer (quantum well) is formed in the middle of the PN junction for emitting light;

The two ends form an optical resonant cavity through mirrors (usually directly using the cutting surface of the chip).

2. Working process

When direct voltage is added to the laser diode, electrons are injected from N region and holes are injected from P region.

Electrons and holes recombine in the active layer to release photons;

These photons reflect back and forth in the resonant cavity, inducing more electrons to recombine and producing stimulated radiation;

When the accumulated light intensity reaches the "threshold current", the laser diode will emit coherent laser.

3. The characteristics of laser diode

Small size: compared with gas lasers and solid-state lasers, LD devices are small and easy to integrate;

High efficiency: electric energy is directly converted into light energy, and the efficiency can reach more than 30%;

Controllable cost: mature mass production, widely used in consumer electronics, industry and medical care;

Wavelength adjustable: covering from visible light to infrared band.

Fourth, the application scenarios of laser diodes

Communication field: optical fiber communication and data transmission require high stability and narrow spectrum width;

Measurement field: laser ranging and laser radar, which require extremely high beam directivity;

Industrial processing: laser welding, cutting and marking require high-power multimode LD;

Medical beauty: laser therapy and skin beauty have special requirements for wavelength accuracy and power;

Consumer electronics: optical storage (DVD, blue light), projection display.

The luminous principle of laser is "stimulated radiation+population inversion+resonant cavity amplification";

The working principle of laser diode is to inject carriers into the semiconductor PN junction, generate stimulated radiation in the active layer, and then amplify it through the resonant cavity, and finally output high-quality laser.

With the advantages of small size, high efficiency and adjustable wavelength, laser diode has become one of the most widely used and demanding core devices in the laser device.

As a professional laser diode supplier, we can provide customers with a full range of products from single mode to multimode, from low power to high power, covering visible light to near infrared band, and support customized services. If you have any requirements for laser diode application or purchase, please feel free to contact us and we will provide you with the most professional solution.