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ECE 631 (Photonics and Devices) Gas Laser (He-Ne) Presentation: Muhsin Caner GÖKÇE Instructor: Prof. Dr. Celal Zaim ÇİL Çankaya University Graduate School of Natural and Applied Sciences Department of Electronic and Communication Engineering
Table Of Contents • Background Information • How it works • Applications • Technical Properties • Pulse Mode (recent Improvements)
Background information Inventions: • 1954 Gordon, Zeiger, Townes: Maser • 1960 Maiman: Ruby-Laser (Al2O3, Solid) • 1961 Helium-Neon Laser (Gas) by Ali Javan in Bell Telephone Laboratories, USA • 1962 Semiconductor-Laser • 1985 Rontgen(X-ray)-Laser
Background information • It is a four level atom laser with a mixture of helium and neon(helium to neon (typically around 7:1 to 10:1) at a pressure of between 2 and 5 Torr (atmospheric pressure is about 760 Torr)). • It operates in Continuous Working (CW) mode(the Helium-Neon laser was the first continuous laser). • Superior beam quality(Gaussian irradiance profile, long coherence length, low divergence angle).
How It Works Excited levels of Helium at 20.61 eV is very close to a level in Neon at 20.66 eV Collision of a helium with neon atom, the energy can betransferred from the Helium to the Neon atom.
How It Works Neon is the lasing gas Visible light and IR Fast radiative transition (spontaneous) The lifetime of s-states is order longer than p states Relevant energy levels of the He-Ne laser. (Ref: Principles of Lasers Orazio Svelto 5. edition)
Applications Red (6328 Å) (Most Common) Yellow (594 nm) (Not efficient) Orange (604.6 and 611.9 nm) (Not Efficient) Green (543.5 nm) (Not efficient) Infrared (1,523.1 nm) (Fiber optic testing) Types of wavelengths
Applications Some of the important applications of He-Ne lasers: • Free-space optical communications • Bar-code scanners • Hologram generation • Fiber Optic Experimentation • Construction of laser light show • Surveillance (ie. audio surveillence) • Tachometer (measuring the rotation speed of a shaft or disk) • Burglar alarm • Gyroscope • Alignment • Interferometry (extracting information about the waves) • Laser printers
Technical Properties Totally reflective mirror Cavity Length (L) 2-5 Torr Rb =75 kΩ Partially reflective mirror 1.2 to3 kV DC Since the discharge has a negative resistance, a ballast resistance is to be used in series with the laser to make the overall impedance positive
Technical Properties FWHM:Gain is at least half of the peak value
CVI Melles Griot Company TEM00 Technical Properties Maximum output is 100mw Long Life (More than 10,000hours) Low divergence angle Rugged, compact and less expensive
CVI Melles Griot Company(TEM00) Technical Properties
CVI Melles Griot Company TEM00 Technical Properties
Technical Properties CVI Melles Griot Company TEM00
Pulse Modes Mode Locking: is a technique which converts CW beam to a periodic series of very short pulsesfrom picoseconds to a nanosecond. Advantages: • High power pulse • All the cavity modes are forced to be in phase Disadvantages: Implementation is diffucult
Pulse Modes (Recent Improvements) Applications: • Photon excitation microscopy • Nuclear fusion • 3D optical data storage • Metal Forming Nano structure
References • (Ref: Principles of Lasers 2010, Orazio Svelto 5. edition page: 444-460) • http://www.cvimellesgriot.com/ • http://www.repairfaq.org/sam/laserhen.htm#henhlc0 • http://www.worldoflasers.com/lasertypes2.htm • ECE 631 lecture notes: http://ece631.cankaya.edu.tr • http://hyperphysics.phy-astr.gsu.edu/hbase/optmod/lasgas.html#c1 • http://www.fou.uib.no/fd/1996/h/404001/kap04.htm