Paper code: <service mark, don’t fill this>
OPTICAL CHARACTERISTICS OF DIFFRACTIVE VARIABLE ATTENUATORS FOR HIGH POWER LASERS
A.G. Poleshchuk, V.P. Korolkov, A.R. Sametov, V.V. Dontsova Institute of Automation and Electrometry SB RAS, Novosibirsk, 630090, Russia
High-power laser radiation is widely used in an industry, medicine and scientific researches. Laser radiation control is a problem facing many laser users. Phase diffractive optical elements (DOE) do not absorb optical radiation but redistribute it in diffraction orders. That is why DOEs are very convenient to control high-power laser radiation especially in UV and DUV spectral ranges.
DOEs usually use the first orders which propagate at an angle to the optic axis. The zero diffraction order propagates without angular deflection, has no restriction on the diffraction efficiency. Zero-order DOEs have some features that make them promising for application in optical systems with high-power lasers. In this paper we report on the optical characteristics of zero order diffractive variable attenuators (DVA) with a binary profile of the structure [1].
The diffractive attenuator is the binary relief microstructure (Fig.1a) fabricated on the surface of the fused silica substrates.
Microstructure looks like a chain of circular sells with about 2 μm period and from 0.3 to 1.6 μm diameter. The attenuator area can be rather large (hundreds of square centimeters) while the minimal sizes of the structure for the UV is about wavelength: 0.35 μm. Laser writing system with circular scanning CLWS-300IAE [2] was used in our experiments for DVA fabrication.
Design of DVA is optimized for λ0, but it can operate over larger spectral range with minor attenuation range decreasing. Thus 1064 nm attenuator with attenuation value about η=100 can work at 920nm wavelength with η=20. Notice that DVA works also at about 1/3 and 1/5 of design wavelength λ0 (see Fig. 1b). Functional dependence of transmission function is remained the same.
Fig. 1c,d shows typical dependence of attenuator transmission from rotation angle. Dynamic range of laser beam transmission adjustment was about η=100-150 from one sample to another sample. DVA can be designed for linear or stepped dependence of transmission from rotation angle. Deviation from linearity was no more then ±5%. Damage threshold was estimated no smaller then 1-2 J/cm2 at 5nc laser pulses duration.
a
Transmission (%)
Wavelength, nm b
Transmission (%)
Transmission (%)
c
Rotation Angle (Degrees) Rotation Angle (Degrees)
d
Fig.1. Relief pattern of DVA (a), spectral response (b) and experimental dependences of attenuator transmission from rotation angle (c, d).
This study was sponsored by Siberia Branch of Russian Academy of Science as a part of the interdisciplinary project №112, fundamental project № 24-8 and Russian Foundation for Basic Research as part of projects №12-02-00974-а и №12-02-01118-а.
References
1. A. G. Poleshchuk, D. E. Denk, A. I. Malyshev. “High-energy diffractive variable attenuator”, Proc. SPIE 6735, 67350R (2007).
2. A.G. Poleshchuk, E.G. Churin, V.P. Koronkevich, V.P. Korolkov, etc. “Polar coordinate laser pattern generator for fabrication of diffractive optical elements with arbitrary structure”, Appl. Opt., 38, pp.1295-1301 (1999).
