1. 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

2. Table Of Contents  Background Information  How it works  Applications  Technical Properties  Pulse Mode (recent Improvements)

3. Background information Inventions: 1954 Gordon, Zeiger, Townes: Maser 1960 Maiman: Ruby-Laser (Al 2 O 3, Solid) 1961 Helium-Neon Laser (Gas) by Ali Javan in Bell Telephone Laboratories, USA 1962 Semiconductor-Laser 1985 Rontgen(X-ray)-Laser

4. 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).

5.  How It Works

6. 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 be transferred from the Helium to the Neon atom.

7.  How It Works Relevant energy levels of the He-Ne laser. (Ref: Principles of Lasers Orazio Svelto 5. edition) Neon is the lasing gas Visible light and IR Fast radiative transition (spontaneous) The lifetime of s-states is order longer than p states

8.  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

9.  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

10.  Technical Properties 1.2 to3 kV DC R b =75 kΩ 2-5 Torr Partially reflective mirror Totally reflective mirror 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 Cavity Length (L)

11.  Technical Properties FWHM: Gain is at least half of the peak value

12. CVI Melles Griot Company TEM00  Technical Properties Maximum output is 100mw Low divergence angle Long Life (More than 10,000 hours) Rugged, compact and less expensive

13. CVI Melles Griot Company(TEM00)  Technical Properties

14. CVI Melles Griot Company TEM00  Technical Properties

15. CVI Melles Griot Company TEM00

16. Pulse Modes Mode Locking: is a technique which converts CW beam to a periodic series of very short pulses from picoseconds to a nanosecond. Advantages:  High power pulse  All the cavity modes are forced to be in phase Disadvantages: Implementation is diffucult

17. Pulse Modes (Recent Improvements) Applications: Photon excitation microscopy Nuclear fusion 3D optical data storage Metal Forming Nano structure

18. 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.trhttp://ece631.cankaya.edu.tr http://hyperphysics.phy- astr.gsu.edu/hbase/optmod/lasgas.html#c1 http://hyperphysics.phy- astr.gsu.edu/hbase/optmod/lasgas.html#c1 http://www.fou.uib.no/fd/1996/h/404001/kap04.htm

19. Thanks for Your Attention