Page 139 - High Power Laser Handbook

108 Diode Lasers Semiconductor Laser Diodes 109

Parameter Value Dimension
L 1.5 mm
R 0.01
f
R r 0.99
λ 970 nm
I 280 mA
th
η 0.93
i
α int 2 1/cm
V 1.35 V
to
R 0.05 Ohm
s
Table 5.1 Typical Values for Laser Parameters

where L is laser cavity length; R and R are the reflectivities from front
r
f
and rear facets, respectively; λ is the lasing wavelength; h is Plank’s
constant; c is the speed of light; and e is electron charge. For a typical
100-mm-wide, 970-nm laser (with parameters given in Table 5.1), the
PCE is 63 percent at 2.5-W output power (2.65-A current). The remain-
ing 37 percent of the power is waste heat and is distributed according
to Fig. 5.7.
Equation (5.1) is only valid for the linear portion of the light ver-
sus current (L-I) characteristic. At higher power, self heating leads to
rollover and additional losses. In general, lasers become less efficient
at higher temperatures. Temperature dependences are usually
described by two phenomenological parameters T and T , which
0
1
6%
10%
Internal quantum efficiency
Internal loss
9%
Threshold current
Excess turn-on voltage
5%
Electrical resistance
Rear facet loss
63% 9% Wall-plug efficiency
0.1%

Figure 5.7 Distribution of total power from a laser diode. In this case,
63 percent of the input power generates useful light, while the remaining
37 percent results in waste heat from the indicated sources.