## On-line beam diagnostic method for high energy laser with large beam profile

Optics Express, Vol. 15, Issue 19, pp. 11763-11768 (2007)

http://dx.doi.org/10.1364/OE.15.011763

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### Abstract

A novel on-line beam diagnostic method for continuous-wave high energy laser (HEL) is presented. The system based on this method is mainly consisted of a scanning circular reflector and a photodetector array disposed spatially. Laser beam passes through the system except a little part of whole beam is sampled and reflected into the detector array by the circular reflector. Through the arithmetic of spatial mapping and image restoration with the output signal of detector array, the spatial-temporal distribution parameters of the laser beam are obtained. The HEL beam of several hundred millimeters in diameter can be on-line measured with spatial resolution of 2 mm and temporal resolution of 30~50ms.

© 2007 Optical Society of America

## 1. Introduction

4. R. Kramer, H. Schwede, and V. Brandl, “Laser beam diagnostics according to ISO and their impact on practical application,” Proc. SPIE **59622H**, 1–8 (2005). [CrossRef]

6. D. Martinen, I. Decker, and H. Wohlfahrt, “Fast spatial-resolved diagnostics of high-power CO_{2} laser beams,” Proc. SPIE **2870**, 225–232 (1996). [CrossRef]

4. R. Kramer, H. Schwede, and V. Brandl, “Laser beam diagnostics according to ISO and their impact on practical application,” Proc. SPIE **59622H**, 1–8 (2005). [CrossRef]

6. D. Martinen, I. Decker, and H. Wohlfahrt, “Fast spatial-resolved diagnostics of high-power CO_{2} laser beams,” Proc. SPIE **2870**, 225–232 (1996). [CrossRef]

7. J. V. Gilse, S. Koczera, and D. Greby, “Direct laser beam diagnostics,” Proc. SPIE **1414**, 45–54, (1991). [CrossRef]

8. G. Rabczuk, P. Kukiello, and R. Zaremba, “Experimental analysis of industrial 1kW CO_{2} laser beam properties,” Proc. SPIE **3571**, 102–106, (1999). [CrossRef]

## 2. Configuration and principle of the system

## 3. Arithmetic of spatial mapping and image restoration

## 3.1 Spatial mapping

*η*detectors are fixed on the aluminous pan evenly, and detector A can be defined as numbered

*i*anti-clockwise from +x axis.

*BC*|=|

*BO*=

*r*| is the radius of the circular reflector, and |

*OA*|=

*R*is the radius of the aluminous pan, ∠

*ABO*=

*α*. Then we can get

*C*(

*ρ*,

*β*) is

*R*and

*r*are constants, so the coordinate of

*C*is only correlative with

*θ*. Thus we can get the mapping polar coordinates of all the detectors from Eqs. (1), (4) and (5) by changing

*θ*. When the reflector is rotated to

*θ*

^{′}from the position of -x axis, that also can be regard as detector array is rotated

*θ*

^{′}relatively,

*θ*should be changed to

*θ*+

*θ*

^{′}. Then we get a matrix of power density of mapping points of all detectors after the circular reflector finished a round trip.

^{-2}mm which can be neglected compared to the system’s spatial resolution of 2 mm, the arithmetic above can be used in not only static condition but also when the reflect rotate continuously.

## 3.2 Image restoration

*k*is the dimension of the pixel, so there are (

*d*/

*k*)·(

*d*/

*k*) pixels distributed evenly in the measurement field of

*d*·

*d*. The process of image restoration and display is shown as Fig. 4.

*F*

^{″}(

*x*

^{′},

*y*

^{′}) in the course of the conversion, which means more than one power density value is “given” to a pixel. So a counter is built to every pixel of

*F*

^{″}(

*x*

^{′},

*y*

^{′}), and the power density values are averaged in the same pixel. Thus we get the power density value of every pixel, and the beam profiles of the measured laser beam as well.

## 4. Experimental applications

## 5. Conclusion

## References and links

1. | C. B. Roundy, “Instrumentation for laser beam profile measurement,” Proc. SPIE |

2. | C. Wang, J. Zhao, and Y. Yuan, “The diagnosis on the spot and drift of CW-COIL laser beam,” Proc. SPIE |

3. | A. R. Marrujo, “High energy laser beam diagostics,” Proc. SPIE |

4. | R. Kramer, H. Schwede, and V. Brandl, “Laser beam diagnostics according to ISO and their impact on practical application,” Proc. SPIE |

5. | T. Yagi, Y. Matsumi, and K. Ohta, “A diagnostic system for an excimer laser beam,” Proc. SPIE |

6. | D. Martinen, I. Decker, and H. Wohlfahrt, “Fast spatial-resolved diagnostics of high-power CO |

7. | J. V. Gilse, S. Koczera, and D. Greby, “Direct laser beam diagnostics,” Proc. SPIE |

8. | G. Rabczuk, P. Kukiello, and R. Zaremba, “Experimental analysis of industrial 1kW CO |

**OCIS Codes**

(040.1240) Detectors : Arrays

(040.5160) Detectors : Photodetectors

(100.3020) Image processing : Image reconstruction-restoration

(120.3940) Instrumentation, measurement, and metrology : Metrology

**ToC Category:**

Instrumentation, Measurement, and Metrology

**History**

Original Manuscript: June 5, 2007

Revised Manuscript: July 25, 2007

Manuscript Accepted: August 7, 2007

Published: August 31, 2007

**Citation**

Shao-wu Chen, Qun-shu Wang, and Hong Zhao, "On-line beam diagnostic method for high energy laser with large beam profile," Opt. Express **15**, 11763-11768 (2007)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-19-11763

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### References

- C. B. Roundy, "Instrumentation for laser beam profile measurement," Proc. SPIE 1625, 318-329 (1992). [CrossRef]
- C. Wang, J. Zhao, and Y. Yuan, "The diagnosis on the spot and drift of CW-COIL laser beam," Proc. SPIE 2869, 289-293, (1997). [CrossRef]
- A. R. Marrujo, "High energy laser beam diagostics," Proc. SPIE 1871, 256-276, (1993).
- R. Kramer, H. Schwede, and V. Brandl, "Laser beam diagnostics according to ISO and their impact on practical application," Proc. SPIE 59622H, 1-8 (2005). [CrossRef]
- T. Yagi, Y. Matsumi, K. Ohta, "A diagnostic system for an excimer laser beam," Proc. SPIE 1031, 378:384, (1988).
- D. Martinen, I. Decker, and H. Wohlfahrt, "Fast spatial-resolved diagnostics of high-power CO2 laser beams," Proc. SPIE 2870, 225-232 (1996). [CrossRef]
- J. V. Gilse, S. Koczera, and D. Greby, "Direct laser beam diagnostics," Proc. SPIE 1414, 45-54, (1991). [CrossRef]
- G. Rabczuk, P. Kukiello, and R. Zaremba, "Experimental analysis of industrial 1kW CO2 laser beam properties," Proc. SPIE 3571, 102-106, (1999). [CrossRef]

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