8 Carbon Dioxide LaserThe CO2 laser operates analogously. N2 is pumped, transferring the energy to CO2.Vibrational energy level diagram depicting the 10.6 micron infrared transition in the carbon dioxide molecule. (The nitrogen vibrational levels shown on the right are used to enhance lasing in laboratory lasers)Image from
9 The Helium Cadmium Laser The population inversion scheme in HeCd is similar to that in HeNe’s except that the active medium isCd+ ions.The laser transitions occur in the blue and the ultraviolet at 442 nm, 354 nm and 325 nm.The UV lines are useful for applications that require short wavelength lasers, such as high precisionprinting on photosensitive materials. Examples include lithography of electronic circuitry and makingmaster copies of compact disks.Text from
10 The Argon Ion Laser Argon lines: Wavelength Relative Power Absolute Power454.6 nm W457.9 nm W465.8 nm W472.7 nm W476.5 nm W488.0 nm W496.5 nm W501.7 nm W514.5 nm W528.7 nm WPopulation inversion is achieved in a two step process. First of all, the electrons in the tube collidewith argon atoms and ionize them according to the scheme:Ar (ground state) + lots of energetic electronsÞ Ar+ (ground state) + (lots + 1) less energetic electrons .The Ar+ ground state has a long lifetime and some of the Ar+ ions are able to collide with moreelectrons before recombining with slow electrons. This puts them into the excited states according to:Ar+ (ground state) + high energy electrons Þ Ar+ (excited state) + lower energy electrons .Since there are six 4p levels as compared to only two 4s levels, the statistics of the collisional processleaves three times as many electrons in the 4p level than in the 4s level. Hence we have populationinversion. Moreover, cascade transitions from higher excited states also facilitates the populationinversion mechanism. The lifetime of the 4p level is 10 ns, which compares to the 1 ns lifetime of the4s level. Hence we satisfy tupper > tlower and lasing is possible.Table fromEnergy level diagram from
11 The Krypton Ion Laser Krypton lines Wavelength Power 406.7 nm .9 W
12 Dye lasersDuarte and Piper, Appl. Opt. 23,Dye lasers are an ideal four-level system, and a given dye will lase over a range of ~100 nm.
13 Dyes cover the visible, near-IR, and near-UV ranges.
14 Titanium: Sapphire (Ti:Sapphire) Absorption and emission spectra of Ti:SapphireUpper level lifetime:3.2 msecoxygenaluminumAl2O3 latticeSlide used with permission from Dan MittlemanTi:Sapphire lases from ~700 nm to ~1000 nm.
16 Some everyday applications of diode lasers Slide provided by Optics I student Kham Ho, 2004A CD burnerLaser Printer
17 Laser Safety Classifications Class I - These lasers are not hazardous.Class IA - A special designation that applies only to lasers that are "not intended for viewing," such as a supermarket laser scanner. The upper power limit of Class IA is 4 mW.Class II - Low-power visible lasers that emit above Class I levels but at a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person.Class IIIA - Intermediate-power lasers (cw: 1-5 mW), which are hazardous only for intrabeam viewing. Most pen-like pointing lasers are in this class.Class IIIB - Moderate-power lasers (~ tens of mW).Class IV - High-power lasers (cw: 500 mW, pulsed: 10 J/cm2 or the diffuse reflection limit), which are hazardous to view under any condition (directly or diffusely scattered), and are a potential fire hazard and a skin hazard. Significant controls are required of Class IV laser facilities.Slide provided by Optics I student Kham Ho, 2004
19 He-Ne Laser ก๊าซ He 1.0 มมปรอท + Ne 0.1 มมปรอท e excite อะตอม He ไปยังหลาย ๆ สถานะ แต่มีสองสถานะที่เป็นอุปสเถียร lifetime = 5ms, 100 msอะตอม He ชนกับอะตอม Ne ถ่ายเทพลังงานให้ Ne ถูก excite เกิด Laser หลาย ๆ ความถี่The excited Ne*(2p4) atom rapidly deexcites to its ground state by emitting additional photons or by collisions with the plasma tube walls. Because of the extreme quickness of the deexcitation process, at any moment in the HeNe plasma, there are more Ne atoms in the 3s2 state than there are in the 2p4 state, and a population inversion is said to be established between these two levels.ใช้ resonator เลือกความถี่ ที่ต้องการ เป็นกระจกสะท้อน 95-99% และกระจกที่สะท้อน 100% เลเซอร์ที่ออกไปมีความเข้มเพียง 1% ของใน resonance cavity