光电子课件lesson_7

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+ laser Ar
structure
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Working chatacteristic
Threshold current, 488nm and 514.5nm (lowest) Drive current
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Absorption and emission spectra of Rhodamine 6G
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Energy level
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Absorption and emission process
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Gas lasers classification
Neutral-atom gas lasers He-Ne laser Cu atom vapor laser Ion gas lasers + Argon (Ar ) ion laser Molecular gas lasers Carbon dioxide (CO2) laser Nitrogen (N2) gas laser Excimer laser
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Liquid lasers
Classification organic dye laser Inorganic liquid laser Advantage wide variety of wavelength (from 340nm to 1.2μm) Narrow spectrum line-width (10~50MHz) ultrashort pulse laser (femto second, 10-15s) Sing pulse energy 10J 8 Peak power 10 W applications: Biomedical, chemical Isotopic separation
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Exciting mode
Optical pumping Electron impact excitation Thermal excitation Chemical energy excitation
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Electron impact excitation
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Working parameters
Mixture gas ratio CO2:N2:He:Xe:H2=1:1.5:8:0.3:0.05 Working pressure: Pd=4400 (Pa· mm) Current: 20mA Voltage: 20kV small-signal gain: G=(0.012~0.0025)d (cm) Saturation gain: Is=72/d2 (W/cm2) Output power: P=14.4 π(I0/ Is)
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Melles Griot company
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Energy level diagram
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The plasma tube
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Working parameters
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Energy level diagram
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Lambda photometrics company
•528.7nm to 476.2nm wavelengths •Up to 7 Watts output power •SHG version giving 200mW @ 257nm •Low noise and excellent beam quality •Multiline mirror holder for all lines operation
Г=R/L
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Carbon dioxide (CO2) laser
Developed in 1965 by Bell Lab Most powerful , most efficient Power: 4000 W in 1967, now 2 × 104W (CW), 1012W (pulse) Energy transfer efficiency: 20%~25% Wavelength: 10.6μm. Applications: cut, weld, scribe, engrave, mark distance test, medical, biology
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Gas lasers
Active medium: gas or vapor Wavelength: from ultraviolet to infrared Excellent beam quality, better than solid-state laser Advantages High output power High transfer efficiency Structure simple Low cost Applications Industry, manufacture Biology, medicine Agriculture
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Vibration modes of CO2 molecule
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Energy level of CO2 molecule
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Essential feature of CO2 laser
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Laser classifications
Active mediums: solid gas liquid semiconductor Wavelength Output time characteristics: mode-locked pulse Q-switched pulse normal-mode pulse continous wave(CW)
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Optical pumping
Definition Normal construction
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Optical pumping
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He-Ne laser
First CW laser, first gas laser Wavelength: visible light, near infrared, 632.8nm
Characteristic: good beam quality, low cost, small size, long operating life, convection cooled, easy power services Volume applications: collimation, test, guidance, accuracy measure, holographical, biology
Definition Two electron impact Process Resonance energy transfer A*+B→A+ B*±∆ E (He-Ne, CO2 laser) Charge transfer A++B→A+ (B+)*±∆ E Penning ionization A * +B→A+ (B+)*±e (slow) (metal vapor laser) Electron collision A+e (fast)→ A*+ e (slow) (N2, Ar+ laser)
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Potential energy curves
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Excimer lasers structure
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Argon ion laser
Highest output power in visiual laser, hundrieds W Wavelength: 488.8nm, 514.5nm Applications DNA sequencing Flow cytometry Semiconductor inspection and repair Hematology High speed printing Photo processing
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Coherent company
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Excimer lasers
Virtus: highly efficiency, featuring compact design, easy installation and operation. Wavelength: from ultraviolet visible light Applications Refractive Surgery Dye Laser Pumping Material Processing and Analysis for Physics, Chemistry Micromachining Marking