Lasers. Conditions of laser operation. Classification of lasers. Continuous wave lasers (He-Ne) Pulsed lasers (Nd-YAG, Ti:Sa)

Transcription

1 Lasers

2 Lasers Conditions of laser operation Classification of lasers Continuous wave lasers (He-Ne) Pulsed lasers (Nd-YAG, Ti:Sa) Ultrashort pulse generation Extreme energies Applications

3 Laser operation Pumping Stimulated emission Population inversion Amplification

4 Absorption and emission Absorption spontaneous emission Stimulated emission LASER = Light amplification by stimulated emission of radiation

5 Laser operation I 0 I 1 I 3 Laser active R = 100% medium R < 100% I 2 Stimulated emission takes place in the laser active medium The emitted photons are reflected from the end mirrors stumulating more photon emission A small part of the photons quit the resonator trough the output coupler

6 Population inversion Why do we need population inversion?

7 What do we need for population inversion? I I 0 I 1 I 3 Laser active R = 100% medium R < 100% I 2

8 Population inversion

9 Two, three and four level systems Two level system Three level system Four level system Fast relaxation Fast relaxation Pumping transition Laser transition Pump transition Laser transition Pumping transition Laser transition Fast relaxation In the best case we get equal population Hitting hard will result in lasing Easy laser operation

10 Classification of lasers By energy: I. class (harmless, laser pointers, CD players etc. ) II.class(< 1 mw, no danger due to the blink) III. class (needs extra attention, < 500 mw), IV. class (extremely dangerous, burning dangers, retina damage etc.)

11 Classification of lasers By the laser active medium: Gas lasers (He-Ne, Ar-ion, CO2, N2, krypton etc.) Solid state lasers (ruby, Nd-YAG, Nd-YLF, Nd-glass, titanium-sapphire) Diode lasers Dye lasers Chemical lasers (I, HF, HBr, stb.)

12 Classification of lasers By operation: CW = continuous wave Pulsed lasers : Q-switched lasers, mode-locking lasers

13 Ruby laser 694,3 nm The first ever operating laser (Theodore Maiman, 1960 ) The laser active medium is chromium doped syntetic sapphire

14 He-Ne laser 7:1 10:1 mixture of He and Ne gas Low pressure (3-7 mbar) Excited helium atoms collide with neon atoms Four level laser

15 Pulsed lasers Q-switched lasers Mode-locked lasers

16 Parameters of pulsed lasers Repetion frequency: 15 Hz 100 MHz Pulse length: ns - fs Energy in one pulse: nj-kj (1.85 National Ignition Facility)

17 National Ignition Facility

18 Rutherford Appleton Laboratory

19 Central Laser Facility, UK ASTRA VULCAN LSF Ultra-high intensity 2.6 kj in sub-picosecond pulses, 100 TW PW Fusion and Plasma Research Extreme UV generation Attosecond pulse generation research Smaller scale lasers Vibrational spectroscopy Imaging; laser tweezers and microscopy

20 Extreme Light Infrastructure

21 Q-switched lasers Maximazing the population inversion then switching out a giant pulse Pulse length: ns

22 Mode-locking

23 Mode locking Superposition of seven modes in random phase (A) And locked phase (B). (Forrás: Enoch Small,1991 2

24 Ultrashort lasers (Ti:sa) The working horse of femtosecond lasers Laser active medium: titanium doped sapphire very good termal properties, wide absorption spectrum) Pulse length: fs Energy: nj-mj Hungarian input: Femtolasers (Krausz Ferenc), R&D Ultrafast Lasers (Szipőcs Róbert)

25 Titanium-sapphire laser

26 Tranziens Biofizika 100 fs, 1 nj, 100 MHz, 800 nm 100 fs, ~ µj, 1 khz, 800 nm Ch BBO CaF 2 A pumpa és próba impulzus térben (és időben) átfed a mintában! St Fotodióda Minta Monokromátor F CCD

27 Applications Time correlated single photon counting (ns, ps, lasers) Microscopy : confocal microscopes, super resolution (CW lasers), two photon microscopy (Ti:sa lasers) FTIR (Fourier transformed infrared spectroscopy) Laser tweezers (CW) Raman spectroscopy (CW lasers) Transient absorption

28 LIBS analysis LIBS = Laser Induced Breakdown Spectroscopy

29 Cleaning the Acropolis

30 Cleaning the Acropolis

31 Laser cleaning

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33 Laser cleaning in Pécs

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