“LASERS” Light Amplification by the Stimulated Emission of Radiation

“LASERS” ….. small Tunable Diode Laser - about 2mm x 2mm chip - used to measure water vapor concentration in the near-IR - used to detect low-levels of gas concentration (ppm, ppb)

“LASERS” ….. Large!!! NOVA Laser at LLNL

“LASERS” Laser Guide Stars - VLT 8.2m telescopes - creates an artificial star at an altitude of 90 km -yellow sodium line - part of the VLT’s Adaptive Optics system

“LASERS” top: CAD model bottom: laser-cut part - 0.5mm thick stainless steel Laser Cutting Laser Welding CO 2, Nd:YAG E ≈ 1MW/cm 2 f beam <.5mm carbon steel, stainless steel, aluminum, titanium

“LASERS” ….. History Albert Einstein describes the photon and points out that stimulated emission of light could occur Arthur Schawlow and Charles Townes publish their theoretical paper "Infrared and Optical Masers" in Physical Review, Theodore Maiman invents the first laser, the optical version of the maser, using a man-made ruby crystal. First operated on May 16, HeNe gas laser is invented by Ali Javan, et al., Bell Labs. -first laser to emit a continuous (CW) beam of light -first output was at 3.39 microns, in the infrared -visible output at microns (633 nm) in "workhorse of the laser industry“ CO 2 gas laser is invented by Patel, Bell Labs Argon ion laser is invented by Bridges, Hughes Research Labs Organic Dye (liquid) laser is invented. 1970's--Semiconductor lasers are run at room temperature, paving the way for their practical use today.

“LASERS” … , the 50 th Anniversary! “A solution looking for a problem.”

“LASERS” ….. Basic Principle Light Amplification by the Stimulated Emission of Radiation Atoms absorb energy… A population inversion is created… The atoms return to their non-energetic states by emitting radiation (“light”--UV, visible, or IR) through stimulated emission… Feedback in an optical cavity amplifies this light… Some of this light is emitted in the form of laser light!

“LASERS” ….. Stimulated Emission

“LASERS” ….. Characteristics of Laser Light

“LASERS”“LASERS” ….. Laser Speckle (random interference pattern)

"How to Make a Laser" "Gain medium (to provide for population inversion)" + "Input source of energy (electricity, light, etc.)" + "Resonant cavity (provides optical feedback and sustains stimulated emission)" “LASERS” ….. Fundamental Parts

“LASERS” ….. Example: The Ruby Laser The RubyLaser - Sapphire crystal doped with chromium ions ( ≈ 0.05%) - The sapphire rod has flat, polished ends coated with gold - The chromium ions absorb the input white-light and emit the laser light - Wavelength of 694 nm (ruby-red color) - Output beam is pulsed - Needs high voltage to run the flash lamp

“LASERS” ….. Example: The Ruby Laser

“LASERS” ….. Example: He-Ne Laser

“LASERS”“LASERS” ….. Example: Red laser pointer

“LASERS” Red Laser Pointer - direct output of red light from the Laser Diode (“LD”) λ = 633nm, 650nm, 670nm, etc. - output is monitored by the built-in photodiode detector (“PD”) -beam expands and is collimated by the aspheric lens “LASERS” ….. Example: Red laser pointer

5mW beam λ = 532 nm “LASERS” ….. Example: Green laser pointer

“LASERS” Diode-Pumped Solid State “DPSS laser” - 808nm (near-infrared) pump diode laser 808nm energy converted to 1064nm by the Nd:YVO 4 crystal nm energy converted to 532nm green light by the KTP crystal - this is a non-linear process called “frequency-doubling” - the input frequency is doubled, and the output wavelength is cut in half - beam is expanded - beam is collimated - beam is filtered to block the (powerful) original IR energy at 808nm “LASERS” ….. Example: Green laser pointer

“LASERS” – Red vs. Green Reference: “Sam’s Laser FAQ”Sam’s Laser FAQ

λ = 405 nm “blue” P = 150 mW λ = 532 nm “green” P=50mW “LASERS” – Red, Green and now Blue!

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