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 SciencesDepartment of Electronic and Communication Engineering

Table Of Contents

Background InformationHow it worksApplicationsTechnical PropertiesPulse 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

How It WorksExcited 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.

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

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

ApplicationsSome 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

1.2 to3 kV DC

Rb =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)

Technical Properties

FWHM: Gain is at least half of the peak value

CVI Melles Griot Company TEM00

Technical Properties

Maximum output is 100mwLow divergence angle

Long Life (More than 10,000 hours)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 ModesMode Locking:is a technique which converts CW beam to a periodic series of very short pulses from picoseconds to a nanosecond. Advantages:High power pulseAll the cavity modes are forced to be in phaseDisadvantages: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#he

nhlc0• http://www.worldoflasers.com/lasertypes2.htm• ECE 631 lecture notes:

http://ece631.cankaya.edu.tr• http://hyperphysics.phy-astr.gsu.edu/hbase/opt

mod/lasgas.html#c1• http://www.fou.uib.no/fd/1996/h/404001/kap04

.htm

Thanks for Your Attention