In one sentence, describe what the following article is about: Lasers work, or "lase," by stimulating electrons to emit light of a particular wavelength. (This process was first proposed in 1917 by Albert Einstein.) For electrons to emit light, they must first absorb energy to boost them to a higher orbit, then discharge that energy as light when returning to their original orbit. These energy sources are known as "pumps." Small lasers, such as those in CD and DVD players and laser pointers, use electronic circuits to provide electric current to diodes, which serves as the pump. Carbon dioxide lasers are pumped with electrical discharges to excite their electrons. Excimer lasers get their energy from chemical reactions. Lasers built around crystals or glasses use strong light sources such as arc or flash lamps. A gain medium, or active laser medium, amplifies the power of the light given off by the stimulated electrons. Gain media can be any of the following items: Semiconductors made of materials such as gallium arsenide, aluminum gallium arsenide, or indium gallium arsenide. Crystals such as the ruby cylinder used in the Hughes Laboratories laser. Sapphire and garnet have also been used, as have fibers of optical glass. These glasses and crystals are treated with ions of rare earth elements Ceramics, which have also been treated with rare earth ions. Liquids, usually dyes, although an infrared laser was produced by using a gin and tonic as the gain medium. Gelatin dessert (Jell-O) has also been used successfully as a gain medium. Gases, such as carbon dioxide, nitrogen, mercury vapor, or a helium-neon mixture. Chemical reactions. Electron beams. Nuclear materials. A uranium laser was first produced in November, 1960, six months after the first ruby laser. These mirrors, or resonators, keep the light within the laser chamber until it builds up to the desired energy level for release, either through a tiny aperture in one of the mirrors or through a lens. The simplest resonator setup, the linear resonator, uses two mirrors placed at opposite sides of the laser chamber. It produces a single output beam. A more complicated setup, the ring resonator, uses three or more mirrors. It may create a single beam, with the help of an optical isolator, or multiple beams. Along with the mirrors, the lens helps concentrate and direct the light so that the gain medium receives as much as possible.
Summary: Provide a source of energy. Channel the energy through a gain medium. Set up mirrors to contain the light. Use a focusing lens to direct the light through the gain medium.

In one sentence, describe what the following article is about: Click on the "Edit" button to the right of the option if you want to be notified by email and/or text message/push notification when someone tries to log into your Facebook using a computer or mobile device you have never used before. Mark the appropriate box with a check. Click on the "Edit" button for Login Approvals, and tick the box that appears if you want your account to require a security code when it is accessed from unknown browsers. Click on the "Edit" button for Code Generator if you want to enable and set up another way to get security codes. Leave unchecked if you want to disable Code Generator. This option defaults at "Code Generator is enabled." Click on the "Edit" button for App Passwords if you want to generate and use special passwords to log into your apps instead of using your Facebook password or Login Approval codes. Click on the "Edit" button for Trusted Contacts if you want to add friends who can securely help you if you ever have trouble accessing your account. The window will then expand to display a clickable "Choose Trusted Contacts" tab so you can add up to five friends to this privileged list. Click on the "Edit" button for Trusted Browsers to review browsers you saved as the ones you often use. When you log into your account using a browser that is not on your Trusted Browsers list, you will be notified. You can remove browsers you don't want to use on this page too. Click on the "Edit" button to Where You're Logged In to review and manage the places where you are logged into Facebook. Should you notice any unfamiliar devices or locations, click on "End Activity" to end the session.
Summary: Edit your login notifications. Impose a security code using Login Approvals. Use your Facebook app to get security codes using Code Generator. Set special passwords using App Passwords. Choose 35 friends to be your Trusted Contacts. Set your Trusted Browsers. Review your login locations via Where You're Logged In.

In one sentence, describe what the following article is about: The rivet should be long enough to get through the material you're using with about 1/8 inch (0.3 cm) to spare. Stack your materials together and measure their height, then add the additional 1/8 inch to find out how long your rivet should be. If your rivets will only be visible from one side like if you're decorating on a leather bag no one will see the inside of you can use a single cap rivet. This will give your project a finished look. If you're making something that you can see the front and back of like the strap of a purse, for example use double-sided rivets. You install these the same way as single cap rivets they just give your project a more finished look. Copper rivets are stronger than regular, silver, "quick" rivets. They're great for using on any leather work that needs some extra strength.
Summary:
Match the length of your rivet to the thickness of your materials. Choose single cap rivets for one-sided projects. Use a double cap rivets for two-sided projects. Select copper rivets for a sturdier finish.