LASER VÀ ỨNG DỤNG (TS. Nguyễn Thanh Phương) - CHƯƠNG 4 potx

LASER VÀ ỨNG DỤNG TS. Nguyễn Thanh Phương Bộ môn Quang học và Quang điện tử Chương IV: Các loại laser và ứng dụng 17/04/2011 3 Chương IV: Các loại laser và ứng dụng Nhắc lại: những yếu tố cấu thành laser • tương tác giữa ánh sáng và vật chất • đảo mật độ tích lũy • môi trường khuếch đại thích hợp • buồng cộng hưởng quang học • tương tác giữa một buồng cộng hưởng quang học và khuếch đại bên trog BCH: -ngưỡng phát laser - so sánh mode và lọc lựa mode - bão hòa khuếch đại -phương trình tốc độ của laser - we now want to get an overview about the different types of lasers, which are practically relevant. IV.1. Laser rắn Chương IV: Các loại laser và ứng dụng 17/04/2011 9 …Ruby (Rubin) continued optical and laser properties of ruby at room temperature IV.1. Laser rắn 17/04/2011 10 Neodymium Lasers 6.3.2. Neodymium LasersIV.1. Laser rắn 17/04/2011 11 • crystal - Nd:YAG is the most important material used for solid state laser systems. YAG stands for Yttrium-Aluminum-Garnet, Y 3 Al 2 O 12 , a colourless, isotropic crystal. For a Nd:YAG laser rod ~1% of the Y 3+ ions is replaces by Nd 3+ ions. The YAG-structure is very stable from lowest to highest temperature, its mechanical stability and workability (growing, grinding, polishing) as well as the achievable optical quality are good. • first realized with glass1961, with YAG 1964. absorption spectrum of Nd:YAG IV.1. Laser rắn 17/04/2011 12 … Nd:Lasers continued - level scheme of Nd:YAG - "strongest" laser transition at 1064.1 nm - lasing is mainly supported by the R 2 sub-level of the 4 F 3/2 level. At room temperature ~40% of 4 F 3/2 atoms are in R 2 (Ê Boltzmann). - lower laser level is 4 I 11/2 with various sub-levels, which all give slightly different emission wavelength. - lower laser levels are thermally not populated, so inversion can easily be achieved, even for cw-operation. - Nd:YAG is a four-level laser, it is homogeneously broadened τ ~240µs fast, non- radiative decay fast, non- radiative decay IV.1. Laser rắn 17/04/2011 13 • applications - material processing (cw and pulsed lasers) welding (Schweißen), marking, writing, drilling (Bohren) (sizes of few µm possible), cutting - illumination and ranging (military) - medical, especially ophthalmology (Augenheilkunde) - pumping of other lasers (e.g. frequency doubled Nd:YAG for pumping of Ti:Sa lasers) and non-linear optics (e.g. frequency doubling [532 nm], tripling [355 nm], quadrupling [256 nm], parametric conversion). - Nd:glass lasers and corresponding amplifiers are also used for laser fusion experiments IV.1. Laser rắn 17/04/2011 14 • discharge pumping - cw-lasers are pumped by diode lasers at ~ 810nm or various types of discharge lamps or filament lamps, pulsed lasers by flash lamps. - energy corresponding to non-radiative decays limits quantum efficiency to ~ 76%. Excess power (~24%) is converted into heat, which has to be dissipated. Light not absorbed by the pump bands is also partially converted into heat - examples for pumping cw-Nd:YAG lasers IV.1. Laser rắn [...]... selection" - the shortest HeNe lasers (~20cm) provide single axial mode oscillation! 17/ 04/ 2011 41 IV.2 Laser khí • common HeNe laser parameters 17/ 04/ 2011 42 IV.2 Laser khí Ar-Ion (Ar+) Lasers 17/ 04/ 2011 43 IV.2 Laser khí • active medium (reminder, see 2.3.5) transition wavelength [nm] - discharge parameters: 3 0-1 50 A/cm2, ~300 K - efficiency (wall plug-to-optical) only ~0.1% → larger Ar+ lasers generate... 17/ 04/ 2011 29 IV.1 Laser rắn • other solid state lasers 17/ 04/ 2011 30 IV.1 Laser rắn … other solid state lasers continued Tuning range for various transition metal solid state lasers large tuning range of Ti:Sa is basis for ultra-short pulse operation 17/ 04/ 2011 31 IV.1 Laser rắn cw-Ti:Sa laser system Coherent MBR 110, tuning range - further information regarding Ti:Sa lasers see 2.3 .4 17/ 04/ 2011 32 Chương. .. better beam profiles - holography (but see comment above) - typical Ar+ laser parameters - medical applications (but see comment above) - laser light shows (but see comment above) 17/ 04/ 2011 45 IV.2 Laser khí • emission wavelength of various nobel gas lasers 17/ 04/ 2011 46 IV.2 Laser khí Excimer Lasers 17/ 04/ 2011 47 IV.2 Laser khí • excimers - excimers are diatomic molecules which do not posses a stable... thermal load ! 17/ 04/ 2011 44 IV.2 Laser khí • applications - Ar+ lasers have been extensively used as pump lasers for dye lasers and cw-TiSa lasers They are now being replaced by all-solid-state laser system, which are based on frequency doubled NdYag lasers (10 64 nm → 532 nm), that are more compact, much more efficient, cheaper, more stable and typically provide better beam profiles - holography (but... lasers see 2.3 .4 17/ 04/ 2011 32 Chương IV: Các loại laser và ứng dụng IV.1 Laser rắn IV.2 Laser khí IV.2 Laser khí • pumping there are different methods of pumping - most common type is based on a continuous or pulsed discharge - optical pumping (with another laser) - gas-dynamical lasers: through fast adiabatic expansion, the gas is transferred to a non-equilibrium state It approaches a new equilibrium... crystal) 17/ 04/ 2011 20 IV.1 Laser rắn … discharge pumping continued - different slab geometries exist single (dual) flash lamp design multiple flash lamp design 17/ 04/ 2011 21 IV.1 Laser rắn … discharge pumping continued - disk geometry beneficial for ultra-high power pulsed solid-state laser systems like those used for laser fusion (at Lawrence Livermore National Laboratory): - better cooling, - larger... stripe diode lasers, 1D-arrays ("bars") or 2D-arrays can be used 17/ 04/ 2011 23 IV.1 Laser rắn … diode pumping continued - there are several geometries for optical pumping with laser diodes • end pumped systems (single and double) - pump light can be matched to mode volume 17/ 04/ 2011 26 IV.1 Laser rắn … diode pumping continued • side pumping of a rod - direct coupling (diodes close to amplifier) - coupling... spin-flip is required (which can not be provided by a fast radiative (i.e electric dipole) transition) 17/ 04/ 2011 38 IV.2 Laser khí HeNe Lasers Note: we have already discussed the HeNe laser amplifier in sec 2.3.5 17/ 04/ 2011 39 IV.2 Laser khí • level scheme (reminder, see 2.3.5) For further information refer to sec 2.3.5 collisions with wall 17/ 04/ 2011 40 IV.2 Laser khí • typical setup - HeNe lasers... (diodes close to amplifier) - coupling with optics - fiber coupling (!) • achievable: optical cw-pumping at ~10kW, cw-output typical 100W, up to ~1kW 17/ 04/ 2011 27 IV.1 Laser rắn … Nd:Lasers continued - physical, optical, thermal properties of Nd:YAG A MISER oscillator (Monolithic Isolated Single-mode End-pumped Ring), or alternatively, an NPRO (Non-Planar Ring-Oscillator): the crystal itself constitutes... typically not compete with dye lasers, solid state lasers, or diode lasers 17/ 04/ 2011 37 IV.2 Laser khí • the role of collisions collisions (between electrons and laser atoms, between gas atoms or between laser atoms and the containing walls) play an important role for gas lasers - collisions with e- transfer atomic population into the upper laser level - collisions between atoms can transfer energy from . LASER VÀ ỨNG DỤNG TS. Nguyễn Thanh Phương Bộ môn Quang học và Quang điện tử Chương IV: Các loại laser và ứng dụng 17/ 04/ 2011 3 Chương IV: Các loại laser và ứng dụng Nhắc. relevant. IV.1. Laser rắn Chương IV: Các loại laser và ứng dụng 17/ 04/ 2011 9 …Ruby (Rubin) continued optical and laser properties of ruby at room temperature IV.1. Laser rắn 17/ 04/ 2011 10 Neodymium Lasers 6.3.2 trog BCH: -ngưỡng phát laser - so sánh mode và lọc lựa mode - bão hòa khuếch đại -phương trình tốc độ của laser - we now want to get an overview about the different types of lasers, which