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The Laser: A Solution Looking for A Problem ?

The Laser: A Solution Looking for A Problem ?. Cockcroft Institute Laser Lectures April 2008. Graeme Hirst STFC Central Laser Facility. This Lecture Series. TODAY 1. The Laser: A Solution Looking for a Problem 2. Radiation Sources: Horses for Courses APRIL 21st

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The Laser: A Solution Looking for A Problem ?

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  1. The Laser: A Solution Looking for A Problem ? • Cockcroft Institute Laser Lectures • April 2008 Graeme HirstSTFC Central Laser Facility

  2. This Lecture Series • TODAY • 1. The Laser: A Solution Looking for a Problem • 2. Radiation Sources: Horses for Courses • APRIL 21st • 3. Laser Science: Come on, How Hard Can It Be ? • 4. Laser Technology or Why is My Ray-Gun so Expensive ? • APRIL 28th • 5. Lasers as Accelerator Subsystems or “What’s the Problem Bob ? • I Don’t Know Alice, It Must Be The Laser.” • 6. Laser Accelerators: The Technology of The Future (They Always Have Been and They Always Will Be ?)

  3. OPPORTUNITIES • Combinations of accelerators and lasers can do things that neither can do on their own • THREATS • If you’re in the accelerator-based light source business then lasersare your most significant competitor • Other accelerator designers are exploiting the possibilities that lasers offer • Laser-based accelerators are being suggested as alternatives to conventional machines • A FACT • Laser technology develops much more quickly than accelerator technology, so things which aren’t an issue today may wellbecome one tomorrow Why Should I Care ?

  4. Prof Colin Webb FRS Health Warning ! “There are two kinds of laser scientist: Those who regard the laser as a black box out of which comes light, And those who regard the universe as a black box into which goes light !” It is important to establish as quickly as possible which kind you’re talking (or listening) to ...

  5. Lecture 1 Plan • Introduction • What’s “the thing” about lasers ? • What types of laser are there ? • Where do lasers fit with respect to accelerators ? • What else are they used for ? • What about safety ?

  6. The Thing(s) About Lasers STIMULATED EMISSION In lasers the light acts on the laser medium to“stimulate” the coherent emission of more light COHERENCE Because laser amplification is coherent, selectivetechniques can be used to generate well-definedbeams from optical noise with high efficiency

  7. The Tree of Life Simplified from http://www.tellapallet.com/tree_of_life.htm Bacteria Archaea PondScum Plants SlimeMoulds Fungi Animals

  8. DiodeLasers The Tree of Life Lasers Simplified from http://www.tellapallet.com/tree_of_life.htm Bacteria Archaea PondScum Plants SlimeMoulds Fungi Animals

  9. The Diode Laser Business • Other • Laser pumping Revenuegrowthhas beenachievedby raisingvolume asunit pricehas fallen • Optical storage (CD, DVD) • Telecommunications • Data from Laser Focus World magazine • Diode laser sales ($M)

  10. DiodeLasers ConventionalLasers The Tree of Life Lasers Simplified from http://www.tellapallet.com/tree_of_life.htm Bacteria Archaea PondScum Plants SlimeMoulds Fungi Animals

  11. The Non-Diode Laser Business • Other • Instrumentation Researchlasersmake up6% of thenon-diodemarket • Basic research • Medical therapeutics • Materials processing • Data from Laser Focus World magazine • Diode laser sales ($M)

  12. DiodeLasers FELs ConventionalLasers The Tree of Life Lasers Simplified from http://www.tellapallet.com/tree_of_life.htm Bacteria Archaea PondScum Plants SlimeMoulds Fungi Animals

  13. It might cost: ~£400k for the laser system, ~£100k for additional optics, diagnostics etc ~£300k+ for a lab with optical tables, utilities, safety systems, HVAC etc +£400k for upgrade to 1J/10Hz Laser Light Sources A “general-purpose” laboratorylight source might give: ~100fs pulses at 800nm ~10nJ/pulse at 80MHz and~2mJ/pulse at 1kHzi.e. Pave 1 watt Near transform-limited anddiffraction-limited output Tunability from >2000nm to<300nm with conversionefficiency from <1% to >10%

  14. Lasers in Accelerators Modern accelerators incorporate lasers for: Photogeneration ofelectron bunches “Heating” of the particle beam Spatial beam diagnosisby “laser wire” X-ray generation byCompton scattering Temporal beam slicing Ultra-low noise clockgeneration and distribution

  15. Lasers as Accelerators High intensity laser pulses induce large electron density changes in plasmas The E-field arising from the electron-ion charge separation can be ~GV/cm Electrons travelling with the plasma wave can acquireGeV energies with DE/E of ~1% and low emittance Issues include: • shot rate i.e. average current • shot-to-shot reproducibility • further reduction of DE/E • length scaling

  16. Attosecond pulse trains can be generated in the VUV by phaselocking laser harmonics Science 305 p1267 (2004) Very Short Pulse Lasers The shortest “direct” pulses come from laserswhose media have gain over a wide spectralbandwidth (Fourier) and whose opticalcavities contain elements which (phase) lockmany cavity modes Commercially available lasers can deliver7 fs pulses at 800 nm where the period is 2.7 fs Time (fs) E field Intensity Intensity envelope

  17. RF Reference Laser locked to RF Laser free-running Free-running fibrelasers have just afew femtosecondsof phase noise atfrequencies above~10kHz (1 partin 1010 stability) w1 wref 2w1 They are becoming the clock of choicefor time-critical acceleratorapplications Very Temporally Stable Lasers Atomic transitions with linewidths <<1Hz are now known and can beused as timing references with stability (much) better than a part in 1015 An issue is the development of an “optical clockwork” to divide the opticalfrequency down to a countable value One approach uses the frequency comb produced by modelocked lasers wref sets the absolute frequencyand beating w1 with 2w1 allowsthe comb spacing to be stabilised (See 2005 Nobel Prize for physics)

  18. A Very Large Laser Schematic The NationalIgnition Facilityat LawrenceLivermoreNational Lab Laser amplifiers Laser pulsegenerator 1.8MJ will bedelivered in192 beamsto a sub-mmDT cryo target Spatial filters Beam transport Targetchamber Nanosecond ablation ofthe target surface will compressthe interior, heating it to a temperaturesufficient to ignite a nuclear fusion reaction

  19. A Very Large Laser

  20. A Very Large Laser France is also buildingone of these

  21. “A gas dynamiclaser is anexplosionwith a cavityround it” The Airborne Laser uses a “MW class” Chemical Oxygen Iodine Laser Chemical efficiency is >30% and supersonic gasflow quickly removes the heat Very High Average Power Lasers Average laser power is limited by: • Efficiency of conversion from pump to output • Ability to cool the laser medium

  22. Fibre lasers’ alternativearchitecture allows easypump coupling and cooling The University of Southampton’sYb-doped “large mode aperture”fibre lasers can deliver>1kW cw Very High Average Power Lasers Laser diodes can be >70% wall-plug efficient and optically-pumpedsolid state stages can be nearly as good The SSHCL at LawrenceLivermore National Labhas delivered 67kWfor 10 seconds and canrun at 10% duty cycle Connections to~MW battery Pump diodes Nd:GGG orNd:YAG/ceramicslabs

  23. SDI - Star Wars In 1983 President Reagan challenged the scientific community “to give usthe means of rendering ... nuclear weapons impotent and obsolete” One option, discussed by Edward Teller, was an array of space-basedDirected Energy Weapons using X-ray lasers pumped by nuclear explosions An independent review* estimated the required on-target fluence to be 3 kJ/cm2and listed many problems with generating and projecting this This idea was judged weaker than “Brilliant Pebbles” *Rev Mod Phys 59 (3) S1, 1987

  24. 3.7 mi.d. Star Wars - Pt 2 S P Bugaev et al,“A 2-kJ,wide-apertureXeCl laser”, Quantum Electronics34 (9) 801, 2004

  25. Laser Safety Laser hazards include: • High power electrical supplies in close proximity to cooling water • Tripping over cables in darkened laboratories • Laser eye damage • Crushing by heavy equipment • Laser skin damage (burns, UV) • Toxic substances • Fire • Collateral radiation (ionising, optical) Maximum permissible exposuresare only ~5 times below the 50%damage threshold The corneal MPE for a sub-10ps,800nm beam is 2.4×10-4 J/m2 The NWSF laser on ERLPgenerates 280 J/m2 unfocused(0.8J, f=60mm, 100fs)

  26. Laser burnedlesion Opticnerve Macula Laser Safety Laser hazards include: • High power electrical supplies in close proximity to cooling water • Tripping over cables in darkened laboratories • Laser eye damage • Crushing by heavy equipment • Laser skin damage (burns, UV) • Toxic substances • Fire • Collateral radiation (ionising, optical)

  27. Conclusions • The range of laser types and capabilities is extremely wide • A multi-billion dollar industry supports diverse applications in telecoms, IT, medicine and manufacturing • In 45 years lasers have gone from a scientific curiosity toan essential laboratory tool • Significant developments continue on timescales of justa few years • So what’s the next problem ... ?

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