Incoherent superpositioning of radiation from a single-mode fiber bundle with 200 mW output power per fiber allows to realize power densities of 2 MW/cm2. The total power being directly scalable with the number of fibers. With special optics for imaging the fiber-bundle endface onto the target instead of simply focusing it is possible to control the power density within that spot. Coherent superpositioning allows to further increase the power density and to direct the beam to a spot within the field of the incoherent superposition. Such systems could be useful for all kinds of applications requiring high-brightness radiation like cutting and welding or laser projection, printing plates, lithography, etc.
Laser diodes with diffraction-limited beam quality offer high power densities of the order of 107 - 108 W/cm2, but are limited in output power to some watts. Scaling to higher powers has to be realized by superposition of a number of laser diodes. Coherent superposition allows us to further increase the power density in the far field. This is realized by injection locking of three slave laser diodes (Toshiba TOLD) 9140, 20 mW, 690 nm) by one master laser diode (TOLD 9140) and superpositioning of the three slaves lasers by a lens array. The feedback of the slaves into the master is suppressed by two Faraday isolators. For superpositioning the light of the slaves while maintaining the high beam quality, the light of each diode is coupled into an optical single-mode fiber. Phase shifts due to mechanical or thermal disturbances of the single-mode fibers for frequencies up to 1 kHz are compensated by a single-mode optical fiber piezoceramic phase modulator and an electronic control circuit. A phase stability with a maximum phase error smaller than 6 degrees is kept over an hour. The power-density distribution in the focal plane of the focusing lens shows a peak power 2.6 times that of the incoherent superposition and a modulation corresponding to the Fourier transform of the nearfield distribution of the lens array.
Laser diodes with diffraction limited beam quality offer high power densities of the order of iO - 108 W/cm2, but are limited in output power to some Watts. Scaling to higher powers without using a solidstate laser converter has to be realized by incoherent superposition of the outputs of a number of laser diodes. For that the radiation of single-mode laser diodes is coupled into single-mode fibers which at the other end are shaped into a bundle of hexagonal symmetry. The radiation leaving the fiber bundle is collimated with an array of achromats and focused with an additional lens onto the target. With 19 fibercoupled 690-nm diodes (TOLD 915 1, 20 mW at the fiber end) a total cw power of 338 mW in a spot of 19.4 jim diameter (at I/Is = l/e2of a nearly Gaussian cross section) was achieved. The peak power density was 263 kW/cm2, which is approximately 1 .7 times that of a single fiber. Optimizing the filling factor should further increase the power density.
Keywords: single-mode lasers diodes, single-mode fibers, scalable system. incoherent coupling
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.