Terminology and History - The first device using amplification by stimulated emission operated at microwave frequencies and was called a maser. - When similar optical devices were developed, they were first known as optical masers. - Today, all devices operating at frequencies higher than microwaves are called lasers (e.g. infrared lasers, ultraviolet lasers, X-ray lasers, gamma-ray lasers). - Devices operating at microwave or lower radio frequencies are called masers. - The back-formed verb to lase is frequently used in the field, meaning to give off coherent light. - The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories. - Theoretical work by Charles H. Townes and Arthur Leonard Schawlow contributed to the development of the first laser. - The word 'laser' originated as an acronym for light amplification by stimulated emission of radiation. - The acronym LOSER (light oscillation by stimulated emission of radiation) has been humorously noted as a more correct option. - The terms 'laser' and 'maser' are also used for naturally occurring coherent emissions in astrophysical and atom lasers. - Albert Einstein established the theoretical foundations for the laser and the maser in 1917. - Rudolf W. Ladenburg confirmed the existence of stimulated emission and negative absorption in 1928. - Valentin A. Fabrikant predicted the use of stimulated emission to amplify short waves in 1939. - Willis E. Lamb and R.C. Retherford found apparent stimulated emission in hydrogen spectra in 1947. - Alfred Kastler proposed the method of optical pumping in 1950. - Joseph Weber presented the idea of using stimulated emissions to make a microwave amplifier in 1951. - Charles H. Townes and his team produced the first microwave amplifier in 1953. - Nikolay Basov and Aleksandr Prokhorov independently solved the problem of continuous-output systems in the Soviet Union. - Prokhorov and Basov suggested optical pumping of a multi-level system as a method for obtaining population inversion in 1955. - Charles H. Townes, Nikolay Basov, and Aleksandr Prokhorov shared the Nobel Prize in Physics in 1964.

Fundamentals of Laser Physics - A laser produces a narrow beam of light in a single wavelength. - Light and other forms of electromagnetic radiation are described as the group behavior of fundamental particles known as photons. - Photons are released and absorbed through electromagnetic interactions with other fundamental particles. - The release of a photon in a laser is triggered by the nearby passage of another photon, known as stimulated emission. - This process allows for the possibility of a chain reaction, where photons trigger stimulated emission in other atoms. - Electrons and their interaction with electromagnetic fields are important in understanding chemistry and physics. - Discrete energy levels of electrons in an atom play a role in absorption and emission of photons. - Stimulated emission and its characteristics are explained by quantum mechanics.

Design and Characteristics of Lasers - Lasers are characterised by their coherence, both spatial and temporal. - Spatial coherence is expressed through the output being a narrow beam, which can be focused to tiny spots or have low divergence. - Temporal coherence implies a polarised wave at a single frequency, with phase correlation along the beam. - Lasers can emit a broad spectrum of light or different wavelengths simultaneously. - Certain lasers are not single spatial mode and have light beams that diverge more than the diffraction limit. - Gain medium, laser pumping energy, high reflector, output coupler, and laser beam are components of a laser. - Mode-locked lasers are capable of emitting extremely short pulses. - The pulses repeat at the round-trip time of the resonator. - Mode-locked lasers are used in femtosecond physics, femtosecond chemistry, and ultrafast science. - Titanium-doped, artificially grown sapphire (Ti:sapphire) is a suitable gain medium for mode-locked lasers. - Consecutive pulses from a mode-locked laser are phase-coherent and identical.

Applications of Lasers - Lasers are used in optical disc drives, laser printers, barcode scanners, DNA sequencing instruments, and fiber-optic communication. - They are also used in semiconducting chip manufacturing, laser surgery and skin treatments, cutting and welding materials, and military and law enforcement devices. - Lasers are employed in laser lighting displays for entertainment purposes. - Semiconductor lasers in the blue to near-UV are used in car headlamps. - Lasers have replaced light-emitting diodes (LEDs) in some applications to excite fluorescence as a white light source.

Operation and Types of Lasers - Lasers can operate in continuous or pulsed mode. - Continuous-wave lasers have constant power output over time. - Many lasers lase in multiple longitudinal modes simultaneously. - Pulsed lasers produce optical power in pulses at a certain repetition rate. - Some lasers cannot be operated in continuous mode due to limitations. - Pulsed pumping is another method of achieving pulsed laser operation. - Flash lamps and other pulsed sources are used to pump the laser material. - Pulsed pumping was historically used with dye lasers. - Three-level lasers require pulsed pumping. - Excimer lasers and copper vapor lasers cannot be operated in continuous wave mode.