Lasers Design and Laser Systems

Lasers Design and Laser Systems Tel: 04-8563674 Nir Dahan Tel: 04-8292151 nirdahan@tx.technion.ac.il Thank You 1

Example isn't another way to teach, it is the only way to teach. -- Albert Einstein Course Subjects Introduction and basic principles The laser medium Resonators Gas lasers Diode lasers Solid-state lasers Other lasers 2

Gas Lasers CO 2 Laser 10.6 micron (9.4 micron) HeNe Laser 632.8nm Argon Ion Lasers 514.5 & 488 & 363.8 & 351.1nm Excimer Lasers F 2 157nm ArCl 175nm ArF 193nm KrCl 222nm KrF 248nm XeBr 282nm XeCl 308nm XeF 351nm Krypton Laser red and yellow lines Metal Vapor Lasers Copper 578 & 510nm Gold 628nm HeCd 325 @442nm CO Laser lines in the window 5-6 microns N 2 Laser 337.1nm Chemical Lasers (HF) The Disciplines in Gas Laser Systems Engineering Physics Chemistry Mechanical (and Opto-Mechanical) design Thermal Design Mirrors & Optical Bench Vacuum & Gas Flow System Control Electrical Engineering Electronics (and microelectronics) circuits Power Supplies Software Industrial design HMI (Human-Machine Interface) System Layout & Packaging Safety Etc. 3

The CO2 Molecule Vibration Modes (V,0,0) (0,V,0) (0,0,V) The CO 2 Energy Levels 4

The CO2 Excitation The CO 2 non-direct Excitation 5

The CO 2 Relaxation He Atoms The CO 2 Direct Current (DC) Excitation V b R V b Slope=1/R Work Line 6

The CO 2 Electrical DC Discharge The CO 2 RF Excitation (Trumpf) 7

The CO 2 RF Excitation (Coherent) The Gas Mixture CO 2 the medium (5%-10%) N 2 excitation interface (for high efficiency) (10%-15%) He relaxation and cooling (80%) Dissociation CO 2 + e CO +O +e ( CO +O - ) CO anti-dissociation H 2 O - anti-dissociation Gold - anti-dissociation catalyst Xe discharge regulation/anti-dissociation (electrons energy distribution) 8

The Gas Mixture The first Solution The Cooling problem and solutions Above 300ºC gas temperature no laser Diffusive Low power and air cooling Water jacket (or other cooling liquid) Axial gas flow (along the tube), or Sealed-off Transverse flow Fast axial flow (FAF) Fast transverse flow Super-sonic nozzle Slab laser (mostly RF excited) + diffusive cooling Combinations of the above 9

The Cooling problem and solutions Simple gas flow 10

Cooling solutions Water jacket cooling in sealed off laser Rofin CO 2 laser Transverse gas flow FAF - Fast Axial Flow Cooling CO 2 Laser 80% He; 15% N 2 ; 5% CO 2 Gas Mixture M=9.6 ρ=0.43 gr/liter (STP); C p =2.46 J/gr K; Assume: Τ=300 K; η=15%; P out =1.5 kw Then: (Heat to be removed) = Q=[P out /η]*(1-η)=8.5 kw And: the mass flow to remove the heat: m=q/[c p Τ]= 11.5gr/sec 26.75 liters/sec (STP); @ 30 torr pressure this is 677 liters/sec Φ=2cm V=2156 m/sec this flow velocity is WAY TOO HIGH!!! 11

Cooling solutions Fast Flow FAF - Fast Axial Flow Cooling CO2 Laser V=270 m/sec Divide the flow into N parallel - flow tubes to reduce the velocity: Reduces the pressure drop (and the pump size ) Reduces the Discharge Voltage drop on the tube 12

FAF - Fast Axial Flow Cooling CO 2 Laser FAF - Fast Axial Flow Cooling CO 2 Laser 13

FAF - Fast Axial Flow Cooling CO 2 Laser FAF - Fast Axial Flow Cooling CO 2 Laser 14

Fast flow along the tubes (Trumpf) Fast flow along the tubes (Trumpf) 15

Fast Flow Benefits Super-sonic nozzle Gas-Dynamic Laser Gas Flow 16

Slab laser + Diffusive Cooling Diffusive Cooling Scaling Rules P max L η = 4 κ T π L 1 η max η 2 π ( a+ b) L PL = 4 κ T 1 η h Max = 80 W/m Max = 30 kw/m 2 17

The CO 2 RF Excitation Scaling with the Electrodes Gap 2 18

Scaling with the Electrodes Width The Resonators 19

Annular RF Excited Laser (Alumor) ICCL Family (Optomic ) Annular Lasers 20

ICCL 1600 (Optomic Lasers) ICCL 1600 TEM 01* Mode 21

Annular Laser Structure (Trumpf) Efficiency of High Power Lasers 22

Sealed-off medical laser (Lumenis) Sealed-off medical laser (Lumenis) 23

Sealed-off medical laser (Lumenis) DC Excited laser main modules The laser head tube including resonator The DC switching power supply The control (electronics & software) 24

DC Excited laser main modules The beam delivery system (application specific) The Team Physicists Physical-Chemistry expert High Voltage Electrical Engineers Opto-Mechanical Engineers Mechanical Engineers Optical Designer Electronics Engineers Real-time Software team Industrial designer Safety expert Medical Applications Expert 25

The Laser Tube structure The internal glass pipe About 10mm diameter Special glass and straight bore site Thin gold coating (pink) The ring hollow cathode Special alloy low sputtering at high voltage (few KV) The output coupler Flat coupler about 90% reflectivity Fixed location vacuum sealing adhesive around the polished pipe facet The Laser Tube structure The rear mirror Spherical full reflective few meters radius of curvature Mounted on a metallic flange Adjustment by screws that push the second flange Glass to metal sealing for the second flange The cooling liquid jacket Part of closed cooling circuit Organic liquid (lower efficiency but no ionization of metal parts) Turbulent (circular) flow in the jacket 26

The Laser Tube structure The gas reservoir Few liters volume Coaxial reservoir The resonator holder symmetric axial expansion The gas path Very long path eliminates external path electric discharge Spring gas pipe or maze path (Laser Industries patent) The sealing High quality vacuum sealing pure glass, Glass to metal, metal gaskets, vacuum adhesive The Fabrication Process Internal glass pipe (in USA) The whole tube internal unique glass shop Thin layer gold coating Front facet polishing using laser alignment Gluing the output coupler around the pipe Assembling the rear mirror Rear mirror preliminary alignment Vacuum pumping for few days & leak tests Low pressure discharge to burn debris CO discharge to initiate the gold catalyst 27

The Fabrication Process Mixture discharge and lasing test burn in Final vacuum pumping Final mixture fill and glass sealing Final burn in discharge for few hours Final laser alignment (power and mode) Some Parameters Model Power (W) Diameter (mm) Length mm Stability (%) Trigger voltage (kv) Operation voltage (kv) Operation current (ma) CO2-SL-34-250 4 φ34 1 250 < 5 6.5-8 4.5-5.5 6-7 CO2-SL-34-280 6 φ34 1 280 < 5 7-8.5 5-6.5 7-8 CO2-SL-34-350 7 φ34 1 350 < 5 9-11 6.5-8 8-12 CO2-SL34-380 8 φ34 1 380 < 5 10-12 7-8.3 8-12 CO2-SL34--400 10 φ34 1 400 < 5 11-13 7.3-8.5 10-12 CO2-SL-34-420 11 φ34 1 420 < 5 11.5-13.5 7.5-9 11-13 CO2-SL-34-450 14 φ34 1 450 < 5 12-15 7.8-9.3 12-15 CO2-SL-38-500 16 φ38 1 500 < 10 13-16 8.5-10 14-18 CO2-SL-54-630 20 φ54 2 630 < 10 15-19 9-10.5 15-20 CO2-SL-54-700 25 φ54 2 700 < 10 16-20 11-12 15-20 CO2-SL-54-800 32 φ54 2 800 < 10 17-22 10-12 20-25 CO2-SL-54-900 35 φ54 2 900 < 10 17-22 11-12 20-25 CO2-SL-54-950 40 φ54 2 950 < 10 17-22 10-12 20-25 CO2-SL-54-1000 45 φ54 2 1000 < 10 20-25 14-15 20-25 CO2-SL-54-1200 55 φ54 2 1200 < 10 22-28 16-17 22-28 CO2-SL-60-1400 60 φ60 2 1400 < 10 25-30 13-17 30-35 CO2-SL-60-1600 70 φ60 2 1600 < 10 28-33 14-18 30-35 28

CO 2 Laser Tube Power vs. Mode 29

CO2 Laser Tube The System Assembly System holder Laser tube in metal vertical pipe HeNe laser red pointer HV switching power supply Closed cooling system Beam delivery articulated arm - alignment High pressure air stream (puff) Cover Safety titles Final tests 30

OEM Modules Sealed-off medical laser 31

Coaxial Laser Old Design 32