Electro-Optics - Applied Optics Fundamentals and Device Applications - page 62

Microlens

FIGURE 2.36
Six-VCSEL array coniguration (current

Copper base

configurations contain nine).

As a starting point, we consider the optical output needed to achieve
a luminous intensity comparable to that of the arc discharge lamp
(25,000 lm). A single-VCSEL array will deliver 70 W at 976 nm. With
1 W = 680 lm at 550 nm, and a correction factor of 7 (assuming a camera QE
of 35% at 550 nm and 5% at 976 nm), the equivalent single-VCSEL output
at 976 nm is about 6800 lm. A 9-VCSEL device will deliver about 61,200 lm
of focused light onto its target. It can be expected that the VCSEL will
improve lighting by more than one f-stop, and the source can be used at
extended distances.
The arrays are connected serially and mounted on a copper base (Figure
2.36). For 150-ms operation, the heat released is about 95 J. The specific heat
of copper is 0.385 J/g°K; therefore, for 100 g of copper submount, the tempera-
ture increase is only 2.5°C, which allows passive cooling.
Nebolsine et al. [85] developed estimates for shaped charge jets and
radiometric characterization with video cameras. The approach was to
determine illumination levels for a laser illuminator needed to overcome
the jet luminosity and provide sufficient exposure for imaging. This gen-
eral concept was used to evaluate candidate laser technologies for suit-
ability in system design. The VCSEL approach provides flexibility, in that
it can be utilized in a range of timing and illumination test scenarios. The
pulse length can be essentially CW, with minimal cooling requirements;
while the illumination brightness can be increased through the addition
of more arrays in the package configuration.

2.11.3 Spectral Matching Considerations

The monochrome spectral response curve for the Vision Research Phantom
V7.3 high-speed video camera used in the author's laboratory is shown
as the dark curve in Figure 2.37. While light sources such as the Luminys
6.5-K lamp exhibit broadband spectral content (Figure 2.38), similar to the