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May 02002 Chuck DiMarzio, Northeastern University 10100-9-1 ECE-1466 Modern Optics Course Notes Part 9 Prof. Charles A. DiMarzio Northeastern University.

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Presentation on theme: "May 02002 Chuck DiMarzio, Northeastern University 10100-9-1 ECE-1466 Modern Optics Course Notes Part 9 Prof. Charles A. DiMarzio Northeastern University."— Presentation transcript:

1 May Chuck DiMarzio, Northeastern University ECE-1466 Modern Optics Course Notes Part 9 Prof. Charles A. DiMarzio Northeastern University Spring 2002

2 May Chuck DiMarzio, Northeastern University Lecture Overview Basics of CW Lasers –Gain –Feedback Pulsed Lasers –MOPA –Gain-Switched –Q-Switched –Mode-Locked

3 May Chuck DiMarzio, Northeastern University Some Material Properties Absorption Energy Emission StimulatedSpontaneous Absorption Emission

4 May Chuck DiMarzio, Northeastern University Laser Gain Materials –Solid Insulating Materials Semiconductors –Liquid eg. Dyes –Gas Pump Mechanisms –Electrical Discharge –Electrical Current –Light Flashlamp Laser –Chemical –Thermal –Other

5 May Chuck DiMarzio, Northeastern University Rate Equations for 2 Levels Energy Populations Photons Actual Rate Equations Include Other Levels as Well

6 May Chuck DiMarzio, Northeastern University Typical Laser Materials Energy Level Pump Fast Laser Energy Level Pump Fast Laser

7 May Chuck DiMarzio, Northeastern University Level Steady State, No Lasing Energy Level Pump

8 May Chuck DiMarzio, Northeastern University Gain vs. Pump R 03 g R 13 g 4-Level 3-Level

9 May Chuck DiMarzio, Northeastern University Feedback f Gain Round Trip

10 May Chuck DiMarzio, Northeastern University Threshold Gain f Gain Round Trip Amplitude Equation

11 May Chuck DiMarzio, Northeastern University Laser Frequency f Gain f Cavity Modes Round Trip Phase Equation

12 May Chuck DiMarzio, Northeastern University Steady State f Gain f Cavity Modes Round Trip Amplitude Equation

13 May Chuck DiMarzio, Northeastern University Gain Saturation Mechanism Laser Light Depletes Upper-State Population Lower Level Has a Fast Decay Time –Laser Does Not Pump Upper Level Populations End Nearly Equal Energy

14 May Chuck DiMarzio, Northeastern University Gain Saturation Modes ff Homogeneously Broadened Line Inhomogeneously Broadened Line

15 May Chuck DiMarzio, Northeastern University Master Oscillator & Power Amp Master Oscillator (CW Laser) Typically a few Watts Modulator Typically E/O With Pulsed Input Power Amplifier 30 dB? for kilowatts output Faraday Isolator Rejects Reflected Light

16 May Chuck DiMarzio, Northeastern University Gain Switched Laser t Pump Gain Power

17 May Chuck DiMarzio, Northeastern University Q-Switched Laser t Pump Gain Power Cavity Q

18 May Chuck DiMarzio, Northeastern University Mode-Locked Laser Modulator at f=FSR Gain Medium f Gain f Cavity Modes

19 May Chuck DiMarzio, Northeastern University Mode Locking Example “Laser” Frequency 10 GHz. (for illustration only) FSR = Modulation Frequency = 100 MHz. 11 Modes Laser Modes Sum Irradiance

20 May Chuck DiMarzio, Northeastern University Second Harmonic a vx (Electron as a Mass on a Spring) a v x

21 May Chuck DiMarzio, Northeastern University Energy Level Diagrams Fluorescence 2-photon

22 May Chuck DiMarzio, Northeastern University Some Lasers (1) Helium Neon –Gas; Elect. Discharge –633 nm Wavelength –milliwatts CW Argon Ion –Gas; Elect. Discharge –514, 488, and others –Watts CW Nd:YAG –Glass; Flashlamp or Laser Pumped –1064 nm –Watts Average Carbon Dioxide –Gas; Elect. Discharge –Around 10.6  m –Watts to kWatts, either CW or pulsed

23 May Chuck DiMarzio, Northeastern University Some Lasers (2) Diode –Elect. Current Low Voltage –Red to NIR –mW and up –Pulsed, Modulated to GHz, and CW –Small non-circular beam output Dyes –Usually Pumped by Another Laser –Typically Visible Wavelengths Usually Quite Widely Tunable (eg. Grating) –nJ or more –Limited Lifetime (often requires flow)

24 May Chuck DiMarzio, Northeastern University Green “Laser” Pointer Laser Diode Nd:YAG Laser Frequency Doubler Battery 780 nm 1064 nm532 nm

25 May Chuck DiMarzio, Northeastern University Titanium Sapphire Laser Laser Diode Nd:YAG Laser Frequency Doubler Power 780 nm 1064 nm532 nm Titanium Sapphire Red to NIR Very Broad Band and Can Be Mode- Locked


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