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Laser Diode Fundamentals
Published in Joachim Piprek, Handbook of Optoelectronic Device Modeling and Simulation, 2017
including the unitless slope efficiency ηs and the threshold current efficiency ηth=(I−Ith)/I. Note that ηs is different from the differential slope efficiency dP/dI and from the averaged slope efficiency P/(I−Ith), which are both given in W/A and not used here. However, this popular analytical model is somewhat ambiguous when the laser experiences relevant self-heating, which causes a sublinear P(I) characteristic as shown in Figure 26.7. Most parameters in Equation 26.8 change as the internal laser temperature rises with increasing current. The threshold current rises together with the threshold carrier density due to declining material gain. The slope efficiency declines due to increasing carrier leakage and/or rising internal absorption.
Light Emitters
Published in David R. Goff, Kimberly Hansen, Michelle K. Stull, Fiber Optic Reference Guide, 2002
David R. Goff, Kimberly Hansen, Michelle K. Stull
Laser optical output is approximately proportional to the drive current above the threshold current. Below the threshold current, the output is from the LED action of the device. Above the threshold, the output dramatically increases as the laser gain increases. Figure 5.19 shows the typical behavior of a laser diode. As operating temperature changes, several effects occur. First, the threshold current changes. The threshold current is always lower at lower temperatures and vice versa. Slope efficiency, the second important parameter, also changes. The slope efficiency is the number of milliwatts or microwatts of light output per milliampere of increased drive current above threshold. Most lasers show a drop in slope efficiency as temperature increases. Figure 5.19 shows that the 50°C curve is not as steep as the curve at the lower temperatures which translates to lower slope efficiency.
Primer on Photonics
Published in Paul R. Prucnal, Bhavin J. Shastri, Malvin Carl Teich, Neuromorphic Photonics, 2017
Paul R. Prucnal, Bhavin J. Shastri, Malvin Carl Teich
The threshold of a real laser is determined by the rate of pumping required to counteract cavity round trip losses. One important consequence of the existence of a threshold is that traditional lasers can never approach perfect efficiency in converting electrical power into optical power, since they must continuously dissipate enough power to keep the gain population inverted in an excited state. The slope of the output optical power solution above threshold is referred to as the slope efficiency, usually stated in terms of Watts/Amp or a quantum efficiency (photons per electrons). Ref. [30] contains a thorough reference on the physical analysis and design of integrated lasers.
Liquid-crystal-based resonant cavities as a strategy to design low-threshold electrically-tunable lasers
Published in Liquid Crystals, 2022
J. Ortega, C. L. Folcia, J. Etxebarria
However, in practice some complication arises: If the reflectivity of the CLC mirrors is very high, the laser performance will be very poor, since most of the amplified radiation inside the cavity cannot escape, and will be eventually absorbed or scattered due to the distributed losses inside the cavity. This pernicious effect can dramatically reduce the slope efficiency of the laser as described in reference [33]. Nevertheless, the existence of a birefringent layer inside the cavity provides a mechanism for the light to escape from the cavity: When the phase retardation of the nematic layer is near but not exactly a full-wave plate, a small proportion of the reflected light is transformed from the reflecting circular polarisation state to the one with opposite handedness, which can escape from the cavity. It is this outgoing radiation what is finally observed as laser emission. Close to the full-wave retardation, the quality factor of the laser is only slightly reduced, still allowing for efficient resonant modes. In general, laser occurs at the wavelength for which the trade-off for both competing effects is the optimum. Furthermore, as can be seen in Figure 2, the laser takes place typically at two or three competing modes simultaneously for a given field.
500 Hz ultraviolet dye laser with pulse energy 1.7 mJ and potential for PLIF imaging
Published in Journal of Modern Optics, 2020
Zhigang Zhou, Deying Chen, Rongwei Fan, Xudong Li, Zhaodong Chen, Tong Luo, Zhiwei Dong, Yugang Jiang
The pulse energies of the fundamental and frequency-doubled dye laser are shown in Figure 4. The energy of the fundamental dye laser increases linearly with the pump laser as shown in Figure 4(a), in which a tunable dye laser is observed when the pump energy surpasses the threshold of 2.4 mJ. The pulse energy of the fundamental laser at 566 nm is 8.1 mJ when the pulse energy of the pump laser is 29 mJ, with a slope efficiency of 31.8% by linear fitting. The pulse energy of the frequency-doubled dye laser at 283 nm versus the output energy of the fundamental laser is shown in Figure 4(b). The energy of the frequency-doubled dye laser is 1.7 mJ at 283 nm when the fundamental pulse energy is 8.1 mJ at 566 nm, with an average output power of 0.85 W at 283 nm. The slop efficiency of frequency doubling is 24.0% by linear fitting. Both the efficiency of fundamental and frequency doubling are comparable to dye lasers at a 10 Hz repetition rate which indicates the saturation effect is suppressed effectively.
Laser emission at the second-order photonic band gap in an electric-field-distorted cholesteric liquid crystal
Published in Liquid Crystals, 2019
J. Ortega, C. L. Folcia, J. Etxebarria
where , , are the lasing, pumping and threshold energies per pulse, respectively, and is the slope efficiency of the laser. From the fitting, we obtained μJ/pulse (0.46 MW/cm2) and %. The laser figure of merit is, therefore, comparable to that of the LWEM of the first-order PBG reported in other works [17,23,24]. This conclusion is at first sight somewhat unexpected, but is in accordance to our theoretical prediction, and supports the viability of high-order modes for practical purposes.