Kontakt

Apl. Prof. Dr. Benno Willke
Apl. Prof. Dr. Benno Willke
Group leader Laser Development & Advanced LIGO
Telefon:+49 511 762-2360Fax:+49 511 762-2784

Benno Willke's homepage

References

[1] T. Kane et al., IEEE J. Quantum Electron. 21, 1195 (1985).

[2] P. Kwee and B. Willke, Appl. Opt. 47, 6022 (2008).

[3] Wiechmann et al., Lasers and Electro-Optics, 1998. CLEO 98. Technical Digest, p 232-233

[4] B. Willke et al., AIP Conference Proceedings 523, 215 (2000); doi: 10.1063/1.1291860

[5] Barillet et al., Meas. Sci. Technol. 7 (1996) 162–169.

[6] Nagano et al., Review of Scientific Instruments 73, 2136 (2002); doi: 10.1063/1.1470230

[7] Willke, Laser & Photon. Rev. (2010) p. 780-793

[8] Winkelmann et al., Applied Physics B: Lasers and Optics (2011) 102, 529-538

[9] Kwee et al., Opt. Express (2012) 20, 10617-10634

[10] Frede et al. , Opt. Express (2007) 15, 459-465

[11] Vahlbruch et al., Class. Quantum Grav. (2010) 27, 084027

[12] Abadi et al., Nature Physics, 2011, 7, 962–965

Low frequency and power noise with NPROs

Experimental setup used to characterize eight different NPRO lasers (see reference [2]). Bild vergrößern
Experimental setup used to characterize eight different NPRO lasers (see reference [2]).

NPROs are laser diode pumped, monolithic ring-oscillators that are available with output powers of up to 2 W (Mephisto family, Coherent). The non-planar beam path in combination with an internal Faraday rotation of the polarization direction and polarization dependent losses cause a linear polarized, single directional operation of the ring laser. The monolithic design reduces vibrations of the resonator mirrors and hence leads to very high frequency stability. Furthermore, a low-noise design of the pump light electronics reduces the power noise of the laser. A specific resonator design leads to a single frequency operation in the fundamental Gaussian mode.

Comparison of the relative power noise of eight different NPRO lasers with operating noise eater. An average of the performance without noise eater is shown as well (see reference [2]). Bild vergrößern
Comparison of the relative power noise of eight different NPRO lasers with operating noise eater. An average of the performance without noise eater is shown as well (see reference [2]). [weniger]

In addition to their low-noise performance the commercial versions of NPROs have fast, large-range actuators for frequency and power control. They also feature an optional internal feed-back control system to reduce the power noise at the relaxation oscillation frequency which – depending on the model – lies between 100 kHz and 1 MHz. A detailed comparative noise characterization of eight commercial NPRO lasers by Kwee et. al. [2] showed a high unit-by-unit reproducibility and a stable operation of one units for 3.5 months.

Power amplification for gravitational-wave detectors

As GWDs need more light power than NPROs can deliver, two concepts were used in the first generation of GWDs: a master-oscillator power-amplifier design for LIGO [3] and injection-locked master-slave systems for GEO600 [4], Virgo [5] and TAMA300 [6]. Both concepts increase the power and preserve the frequency stability of the NPRO master laser. Even though the NPRO's frequency noise is among the lowest of commercially available Nd:YAG lasers, GWDs require a reduction of this noise by several orders of magnitude. This is achieved by nested feed-back control loops which use the NPRO's frequency control actuators (a fast actuator up to 100 kHz and a long-range slow actuator). An overview of the laser stabilization for GWDs can be found in reference [7].
 
The first generation of GWDs was operated continuously for 24 hours a day, seven days a week for more than 10 years. During this time the different NPRO master lasers (different vendor and different output power levels) worked stably and reliably.

 
Zur Redakteursansicht
loading content