Types of Lasers

1. Types of Lasers • Solid-state lasers • Dye lasers • Gas lasers

2. Absorption blue Green l (nm) 300 400 500 600 700 Rapid non-radiative transitions Flashtube High reflector mirror Semi-transparent mirror Ruby Rod Metastable state Output green blue 694.3 nm Ground state Power supply Energy levels of chromium ions in ruby The Ruby Laser ถูกสร้างในปี 1960 โดย Ted Maiman เป็นเลเซอร์ชนิดแรก ตัวกลางขยายแสงคือทับทิม เป็นผลึกของ Al2O3 ที่ ไอออนส่วนน้อยของ Al3+ ถูกแทนที่ด้วยไอออนของ Cr3+ แสงสีเขียว, น้ำเงินจากหลอดซีนอนเป็นตัวกระตุ้นอะตอมโครเมียม

3. pumping bands non-radiative decay Flash lamp or diode laser pumping 1.064 mm non-radiative decay Ground state Energy levels of Nd3+:YAG Nd3+:YAG Laser Nd3+- dopedYAGNd = NeodymiumYAG = Y3Al5O12= Yttrium Aluminium Garnet

4. pumping bands phonon emission laser pumping tunable laser emission Energy levels of Ti3+:Al2O3 Ti3+:sapphire Laser *Titanium-doped sapphire

5. P-type N-type Current control Semiconductor Diode Lasers

6. Gas Lasers

7. The Helium-Neon Laser He: Ne = 5:1

8. Carbon Dioxide Laser The CO2 laser operates analogously. N2 is pumped, transferring the energy to CO2.

9. The Helium Cadmium Laser The population inversion scheme in HeCd is similar to that in HeNe’s except that the active medium is Cd+ ions. The laser transitions occur in the blue and the ultraviolet at 442 nm, 354 nm and 325 nm. The UV lines are useful for applications that require short wavelength lasers, such as high precision printing on photosensitive materials. Examples include lithography of electronic circuitry and making master copies of compact disks.

10. The Argon Ion Laser Argon lines: WavelengthRelative Power Absolute Power 454.6 nm .03 .8 W 457.9 nm .06 1.5 W 465.8 nm .03 .8 W 472.7 nm .05 1.3 W 476.5 nm .12 3.0 W 488.0 nm .32 8.0 W 496.5 nm .12 3.0 W 501.7 nm .07 1.8 W 514.5 nm .40 10.0 W 528.7 nm .07 1.8 W

11. The Krypton Ion Laser Krypton lines WavelengthPower 406.7 nm .9 W 413.1 nm 1.8 W 415.4 nm .28 W 468.0 nm .5 W 476.2 nm .4 W 482.5 nm .4 W 520.8 nm .7 W 530.9 nm 1.5 W 568.2 nm 1.1 W 647.1 nm 3.5 W 676.4 nm 1.2 W

12. Dye lasers Dye lasers are an ideal four-level system, and a given dye will lase over a range of ~100 nm.

13. Dyes cover the visible, near-IR, and near-UV ranges.

14. Absorption and emission spectra of Ti:Sapphire Upper level lifetime: 3.2 msec Al2O3 lattice oxygen aluminum Titanium: Sapphire (Ti:Sapphire) Ti:Sapphire lases from ~700 nm to ~1000 nm.

15. Diode Lasers

16. Some everyday applications of diode lasers A CD burner Laser Printer

17. Laser Safety Classifications • Class I - These lasers are not hazardous. • Class IA - A special designation that applies only to lasers that are "not intended for viewing," such as a supermarket laser scanner. The upper power limit of Class IA is 4 mW. • Class II - Low-power visible lasers that emit above Class I levels but at a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person. • Class IIIA - Intermediate-power lasers (cw: 1-5 mW), which are hazardous only for intrabeam viewing. Most pen-like pointing lasers are in this class. • Class IIIB - Moderate-power lasers (~ tens of mW). • Class IV - High-power lasers (cw: 500 mW, pulsed: 10 J/cm2 or the diffuse reflection limit), which are hazardous to view under any condition (directly or diffusely scattered), and are a potential fire hazard and a skin hazard. Significant controls are required of Class IV laser facilities.

19. He-Ne Laser

21. Laser Diode • F.B. ผ่าน pn junction เป็นการฉีด e และ hole ไป recombine เกิด แสง • กระจก 2 อันห่างกัน L ทำหน้าที่สะท้อนแสงกลับไป-มา เป็น Fabry-Perot อีก 2 ด้านเป็นผิวหยาบเพื่อให้โฟตอนทะลุผ่านออกไป ดังนั้นโฟตอนเฉพาะ resonance modes ที่จะไปกระตุ้นให้กิดเลเซอร์ต่อไป

22. Table 3. Semiconductor Laser Materials. Wavelength Wavelength Material Material (ต m) (ต m) ZnS 0.33 GaAs 0.84-0.95 ZnO 0.37 InP 0.91 Gan 0.40 GaSb 1.55 ZnSe 0.46 InAs 3.1 CdS 0.49 Te 3.72 ZnTe 0.53 PbS 4.3 GaSe 0.59 InSb 5.2 CdSe 0.675 PbTe 6.5 CdTe 0.785 PbSe 8.5