Conversion efficiency of 6.X nm Emitted from Nd:YAG and CO 2 Laser Produced Plasma

Transcription

1 S29, Tuesday Morning Conversion efficiency of 6.X nm Emitted from Nd:YAG and CO 2 Laser Produced Plasma Shinsuke Fujioka 1 1 Institute of Laser Engineering, Osaka University!! H. Nishimura 1, M. Miyake *,1, T. Ugomori 1,! M. Yoshida *, H. Azechi 1! * Dep. Eng., Kinki University, Japan!!! 2011 International Workshop on EUV and Soft X-ray Sources Dublin, Ireland, November 7 10, 2011!!

2 Summary Conversion efficiency, angular distribution, spatial profile of 6.X nm emission were measured by using Co/C multilayer mirrors % of the conversion efficiency has been attained with 1 x x W/cm 2 of Nd:YAG laser intensity and Gadolinium targets. Conversion efficiency depends weakly on durations of Nd:YAG laser pulse. Minimum thickness of Gadolinium layer is 400 nm for sufficient 6.X nm emission. Punch-out scheme will be studied to supply minimum mass Gadolinium targets.

3 6.X nm is selected, because La/B 4 C and Mo/B 4 C multilayer mirror has high reflectivity for the light. 100 Reported reflectivity of MLMs in EUV range 6.7 nm 13.5 nm 80 Reflectivity (%) Wavelength (nm)

4 The 6.X calorimeter consists of two Co/C mirrors and a photodiode. Co/C mirror Co/C mirror Laser diode Co/C mirror Iris B Co/C mirror Laser diode! Entrance Aperture! (3.8 mmφ) Iris Pinhole! (1 mmφ) Al mirror Entrance! Aperture! (3.8 mmφ)! Iris A Iris C Iris D Pinhole! (1 mmφ) Al mirror! (movable) cigar! (scale reference) Al mirror! Al mirror! Breadboard X-ray photodiode Breadboard X-ray photodiode! We have prepared the following diagnostics: Mini-calorimeter to measure angular distribution of emission. Monochromatic 6.X nm imager to identify emission dominant region lines/mm reflective grating spectrometer lines/mm transmission grating spectrometer.

5 The Co/C mirrors has a wide bandwidth. Flexible for change of the targeted wavelength. 3.0 Measured reflectivity of Co/C in EUV range Reflectivity (%) nm Wavelength (nm) Fabricated by Rigaku Innovative Technology

6 Energy, spectrum, in-band image, and angular distribution were measured. Spectrometer In-band imager Nd:YAG laser Wavelength: 64 µm Pulse duration: 2 ~ 10 ns (tunable) Energy: 0.1 ~ 50 J (tunable) Spot size 100 or 250 µm (tunable) Laser Mini-calorimeter 30,45,60,75,90 degs. CO 2 laser Wavelength: 10.6 µm Pulse duration: 30 ~ 40 ns (fixed) Energy: 0.1 J (fixed) Spot size 100 µm (fixed) Calorimeter

7 6.X images show the emission region becomes lager by longer duration of irradiated laser pulse. In-band images of Gd plasmas 3 ~ 4 ns LASER Normalized intensity ~ 4 ns 7 ~ 9 ns LASER Normalized intensity Position (µm) 7 ~ 9 ns Position (µm)

8 Angular distribution for 7-9 ns is more anisotropic (γ = 0.63) compared to that for 3-4 ns (γ = 0.55). Angular distribution of 6.7 nm light emission ~ 4 ns 7 ~ 9 ns Relative intensity Relative intensity Angle (deg.) cos 0.55! cos 0.63! Angle (deg.) 80 This is consistent with the in-band images.

9 6.X nm CEs depend weakly on the pulse duration % of CEs are attained with Nd:YAG laser. Energy conversion efficiency from laser to 6.7 nm within 2%BW (a) 2.0 (b) 2.0 Conversion efficiency (%) Conversion efficiency (%) Intensity (W/cm 2 ) 3-4 ns 7 9 ns Intensity (W/cm 2 ) Dependence of EUV-CEs on pulse duration is small compared to that on a Sn-based 13.5 nm source.

10 Spectrum and CE have been measured to identify thickness required for sufficient in-band emission. Intensity (arb. unit) Spectrum vs. Thickness 100 nm 50 nm 30 nm Bulk Normalized CE CE vs. Thickness Thickness Glass Gadlinium 100, 50, 30, 10 nm! 400 nm nm Wavelength (nm) Layer thickness (nm) 400 nm thickness is required for sufficient in-band emission.

11 Punch-out scheme will be studied to supply minimum mass Gd targets for a clean and powerful source. Schematic of the punch-out scheme Transmissive substrate! Thin Gd layer! Punched-out Gd (pre-expanded)! Heating laser Punch-out laser ~ 10 9 W/cm 2 > 100 m/s! Minimization of ionic- and neutral debris generation. High-speed and -repetition supply of Gd target. Easy to synchronize with the heating laser.

12 High melting temperature (1600 K) of Gadolinium may be preferable for the punch-out scheme. Shadow images of punched-out Sn mm Scattered image 10mm 5mm 2µs 4µs 6µs 8µs 10µs 12µs Melted tin layer is broken into particles and droplets.

13 Summary Conversion efficiency, angular distribution, spatial profile of 6.X nm emission were measured by using Co/C multilayer mirrors % of the conversion efficiency has been attained with 1 x x W/cm 2 of Nd:YAG laser intensity and Gadolinium targets. Conversion efficiency depends weakly on durations of Nd:YAG laser pulse. Minimum thickness of Gadolinium layer is 400 nm for sufficient 6.X nm emission. Punch-out scheme will be studied to supply minimum mass Gadolinium targets.