Individual Collimating Lenses
Heatsink Diode Bar
Mounted Bar Assembly x 5
Diode Bar Diode Bar Diode Bar Diode Bar Diode Bar
P Ceramic Backplane Single Optic
N
Pyroelectric Detectors - Lithium tantalate
- Spectral range 2 ... 25 µm P N Ceramic Backplane 5-Bar Stack
Figure 1 top: current manufacturing method used by northrop grumman cutting Edge optronics (ngcEo) for lensed QcW diode arrays. Bottom: proposed manufacturing method for high density stack (hDs) arrays for the liFE programme. ngcEo offers commercial products with up to 20 bars per stack, and signifi cantly larger stacks could be produced for the liFE programme Source: Feeler et al, Proceedings of SPIE Volume: 7916
diodes used for the same application.’ Feeler believes that if the laser diode industry
were to invest in its manufacturing techniques and use lessons learned from the semiconductor industry, the industry could make laser diodes at the right price and performance for future fusion power plants. Today’s laser diode manufacturing techniques
have several drawbacks. They are currently made in a labour-intensive way that cannot be scaled up easily. The material cost of the heatsinks is of the same order of magnitude as the material cost of the laser diode bars and the use of individual collimating lenses cannot likely be scaled to meet fusion power plant cost targets. To solve some of these problems, NGCEO has developed a process for making non-lensed high-density stacked (HDS) arrays with a bar-to-bar pitch of 150µm that is well-suited to the requirements of laser fusion power plants. The proposed process is shown in Figure 1 for a fi ve-bar stack, but NGCEO has fabricated non-lensed versions
parameter
Bar power (W) Bar pitch (µm)
Intensity (kW/cm2 )
HDS array size (# of bars) Power/HDS array (kW)
of this type of array containing anywhere from two to 20 bars. A lensed version of this type of array, with one large optical element collimating each HDS array, is a natural progression of existing technologies and would meet the stated requirements of fusion power plants. According to Feeler, the industry needs to eliminate modularity, use more automation (as seen in the semiconductor industry), and increase the power density of the diodes. ‘If we can get more power out of each diode bar then we will need fewer bars,’ he says. ‘Maximum peak power is currently around 300 to 400W, but there is no technical reason why we should not achieve the 1,000W needed by power plants.’ But changing manufacturing techniques
requires a lot of investment, and Feeler admits that, while the research has been done and the company is theoretically ready to make those changes, there is currently little motivation to do so. ‘At the moment, there is nothing pushing us to invest in our capacity at these extreme
2011 (commercially available) 300-400 150 ~ 25 20 6
LIFE Requirements Power requirement – demo fusion engine HDS arrays required Target price / array
Target price / packaged bar
~ 2020 500 100 ~ 50 100 50
~ 100 GW ~ 2 million $250-$1000 $2.50
the laser diode industry still has a way to go before meeting the requirements for laser-driven power plants such as liFE Source: Feeler et al, Proceedings of SPIE Volume: 7916
www.electrooptics.com
Extensive Detector Range
Single-channel Multi-channel
Multi-element detector
➤
Detector with built-in micromachined
InfraTec GmbH headquarters
Dresden - GERMANY
InfraTec - Infrared Sensor and Measurement Technology Ltd. Chesterfield - UK
Call us at +44 1246 267562 E-Mail:
sensor@InfraTec.co.uk Internet:
www.InfraTec.co.uk
MARCH 2011 l ElEctro optics
17
See us at
mtec 6-7 April 2011 Birmingham, UK
booth 1219
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