The word "laser" is actually the acronym for "Light Amplification by Stimulated Emission of Radiation", or "Amplification of light by means of the stimulated emission of radiation". The first laser in history was developed in 1960 at the Hughes laboratories in California, and used a silver-coated ruby cylinder as a resonator. Nowadays lasers are used for various applications, from measurements to reading encoded data, and they can be built in different ways, depending on the budget available and technical skills.
Steps
Part 1 of 2: Understanding the Principle of Operation of a Laser
Step 1. Provide the power source
The physical principle on which the operation of a laser is based is that of stimulated emission, which consists in stimulating electrons to emit light at a particular wavelength (this process was initially proposed by Albert Einstein in 1917). In order for them to emit light, the electrons must absorb enough energy to allow them to jump to an orbit farther from the nucleus, and then discharge this energy, in the form of light, when they return to their original orbit. The sources of energy are called "pumps".
- Small lasers, such as those used in CD / DVD players and laser pointers, use electrical current supplied to the diode through electronic circuits as a “pump”.
- Carbon dioxide lasers are "pumped" through electrical discharges that excite electrons.
- Excimer lasers obtain energy from chemical reactions.
- Crystal or glass-based lasers employ powerful light sources, such as arc lamps or flashes.
Step 2. Channel energy through an active medium
An active medium (called "gain medium" or "active laser medium") amplifies the power of the light emitted by the stimulated electrons. Depending on the type of laser, the active medium can consist of:
- Semiconductor materials, such as gallium arsenide, aluminum gallium arsenide, or indium gallium arsenide.
- Crystals, such as the ruby cylinder used for the construction of the first laser in the Hughes laboratories. Sapphire and garnet were also used, as were optical fibers. These glasses and crystals are treated with rare earth ions.
- Ceramics, also treated with rare earth ions.
- Liquids, usually dyes, although an infrared laser was made using gin and tonic water as the active medium. A jelly dessert (the popular US "Jell-O") has also been used successfully as an active medium.
- Gases, such as carbon dioxide, nitrogen, mercury vapor, or a mixture of helium and neon.
- Chemical reactions.
- Electron beams.
- Radioactive materials. A uranium laser was first built in November 1960, just six months after the first ruby laser.
Step 3. Assemble the mirrors to hold the light
These mirrors, called resonators, keep the light inside the laser cavity until, once the desired level is reached, the energy is released through a small opening in one of the mirrors, or through a lens.
- The simplest resonator scheme is the linear resonator, which employs two mirrors placed at the ends of the laser cavity. In this way, a single beam is generated at the exit.
- A more complicated scheme, called a ring resonator, is based on the use of three or more mirrors. It is possible to generate a single beam, with the help of an optical isolator, or a multiple beam.
Step 4. Use a focusing lens to direct light through the active medium
Together with the mirrors, the lens helps to concentrate the light and direct it as much as possible towards the active medium.
Part 2 of 2: Building a Laser
Method 1: Assembling a Laser in Kit
Step 1. Find a reseller
You can go to an electronics store or search the internet for a "Laser Kit", "Laser Module", or "Laser Diode". A complete laser kit includes:
- A driver circuit. Try to get a driver circuit that allows you to regulate the current (the driver circuit is sometimes sold separately).
- A laser diode.
- An adjustable collimation lens (Adjustable Lens) made of glass or plastic. Typically the diode and lens are already assembled together in a small tube (sometimes these components are sold separately from the driver circuit).
Step 2. Assemble the driver circuit
Many laser kits require the assembly of the pilot circuit. These kits provide the motherboard and related parts, which must be soldered on the board following the attached diagram. Other kits may instead include the pilot circuit already assembled.
- With a little experience in electronics, it is also possible to design the driver circuit yourself. The LM317 driver circuit is a great starting scheme for designing your circuit. In this case, be sure to use an RC circuit (resistor-capacitor) in order to protect the output power from voltage peaks.
- Once the driver circuit is assembled, you can test it by connecting an LED diode to it. If the LED doesn't light up, try adjusting the potentiometer. If the LED still doesn't light up, check the circuit and make sure all connections are okay.
Step 3. Connect the driver circuit to the diode
If you have a digital multimeter available, you can connect it to the circuit and monitor the current received by the diode. Most diodes operate between 30 and 250 milliamps (mA), and produce a sufficiently powerful beam between 100mA and 150mA.
Although a greater power of light emitted by the diode results in a greater power of the laser beam, the further increase in current required to obtain such power would quickly burn the diode
Step 4. Connect the power supply (battery) to the driving circuit
The diode should now emit quite bright light.
Step 5. Adjust the collimation lens to focus the laser beam
If you're aiming at a wall, adjust the lens until you get a sharp, bright spot.
Once in focus, place a match in the path of the laser beam and adjust the lens again until the match head begins to catch fire. You can also try popping a balloon or burning a sheet of paper
Method 2: Build a Laser by Retrieving the Diode from a Burner
Step 1. Get an old DVD or Blu-Ray burner
Look for a device with a write speed of at least 16x. These devices employ diodes with at least 150 milliWatts (mW) of power.
- DVD writers employ a red light diode, with a wavelength of 650 nenometers (nm).
- Blu-Ray writers use a blue light diode, with a wavelength of 450 nm.
- Even if it is unable to complete a burn, the burner must be functional (in other words, the diode inside it must be working).
- Do not use a DVD player or CD player / burner in place of a DVD burner. A DVD player contains a red light diode, but with less power than a DVD burner. The diode of a CD burner, on the other hand, has sufficient power, but emits light in the infrared field (not visible to the human eye), and therefore it would be impossible for you to see the beam.
Step 2. Remove the diode from the burner
First you need to turn the player upside down; at this point you will see four or more screws that must be unscrewed in order to access the diode.
- Once the player is disassembled, you will see a couple of metal rails held by screws. These guides support the optical head. Once the guides are removed, you can also remove the print head.
- The diode will be smaller than a dime. It has three feet and could be mounted on a metal support, with or without a protective transparent window, or naked.
- At this point, the diode must be removed from the head. It may be easier to remove the heatsink before taking out the diode. If you have an antistatic bracelet available, use it while removing the diode.
- Handle the diode with care, especially if it does not have a metal support. In this case, you may need an antistatic container to preserve the diode until it is time to install it in the laser.
Step 3. Get a converging lens
The light beam from the diode will need to pass through the lens for it to act as a laser. You can achieve this in two ways:
- Using a magnifying glass to focus: To get a laser beam, you'll need to adjust the position of the lens until you get a point, and you'll have to repeat this every time you use the laser.
- By directly procuring a laser module equipped with a collimator: laser modules with low power diodes (around 5 mW) are quite cheap; you can buy one of these laser modules, and replace the diode inside with the one taken out of the DVD burner.
Step 4. Obtain or assemble the driver circuit
Step 5. Connect the diode to the driver circuit
Connect the positive pin of the diode (anode) to the positive lead of the circuit and the negative pin of the diode (cathode) to the negative lead of the circuit. The position of the pins in the diode differs depending on whether it is a red light diode on a DVD writer or a blue light diode on a Blu-Ray writer.
- Hold the diode with the pins facing you, and rotate it so that the pin heads form a triangle pointing to the right. In both cases, the upper foot is the anode (positive).
- In DVD burner red light diodes, the middle pin, which represents the tip of the triangle pointing to the right, is the cathode (negative).
- In the blue light diodes of Blu-Ray writers, the bottom pin is the cathode (negative).
Step 6. Connect the driver circuit to the power supply (battery)
Step 7. Adjust the collimation lens to focus the laser beam
Advice
- The more concentrated the laser beam, the greater its power. The laser, however, will only be effective at the distance for which it is in focus: if you focus the beam at a distance of one meter, it will only be effective at one meter. When you're not using the laser, out-of-focus the lens until you get a beam the diameter of a ping-pong ball.
- To protect the newly assembled laser, you can use a metal box as a container: for example, the casing of an LED lamp or a battery charger, depending on the size of the driving circuit you used.
Warnings
- Always wear protective goggles calibrated for the wavelength of your laser (specifically the wavelength of the laser diode). The color of the protective goggles is complementary to that of the laser beam: they will be green for a 650 nm red light laser, and red-orange for a 450 nm blue light laser. Never use a welding mask, blackout glasses or sunglasses instead of protective goggles.
- Do not look directly into the laser beam, and do not point it at other people. Class IIIb lasers, such as the one described in this article, can damage your eyes even if you are wearing protective eyewear. It is also illegal to indiscriminately aim a laser of this type.
- Do not aim the laser at reflective surfaces. A laser is a beam of light, and, like light, it is reflected, although the consequences can be more serious.
