coated with positive-type photoresist (AZ-1350) and exposed[23] T. Kobayashi, T. Kawakami, and Y. Furukawa, ''Thermal diagnoto mercury light for 1 minute after prebaking at 90°C for 20 sis of dark lines in degraded GaAs-AlGaAs double-heterostructure minutes. Then, the lasers were operated at 20"C, 5 mW/facet for lasers," Japan. J. Appl. Phys., vol. 14, pp. 508-515, Apr. 1975. 20 minutes. After this, they were syringed in the acetone solution, with ultrasonic vibration, for 3 minutes. The photoresists coated on three lasers were completely dissolved, but in two lasers, no matter what, only part of the photoresist coated at the emitting area could not be dissolved. Note that remaining photoresist was observed on either, but not both, mirrors of the laser. The actinic absorbance of the photoresist decays suddenly in light with a wavelength above 0.5 pm, so 0.8 pm radiation from a laser is transparent to the photoresist. We have certified that photoresist baked at 150°C for 20 minutes could be dissolved completely in the acetone solution, but not 180°C for 20 minutes. Thus, we concluded that a temperature rise of about 150°C did take place at the mirror surface at least in two lasers. Similar results have been presented by 0. Matsuda et al. at the 26th Nat.Conv. Japan. SOC. Appl. Phys., Spring 1979 (in Japanese). Y. Nannichi, J. Matsui, and K. Ishida, "Rapid degradation in double-heterostructue lasers-11: Semiquantitative analyses on the propagation of dark line defects," Japan. J. Appl. Phys., vol. 14, pp. 1561vol. 14, pp. -1568vol. 14, pp. , Oct. 1975.
Influence of Optical Feedback on Laser Frequency Spectrum and Threshold ConditionsJENS HENRIK OSMUNDSEN AND NIELS GADE Abstruct-The steady state behavior of the external cavity operated laser has been analyzed, taking into account multiple reflections.The effect of optical feedback is included in the phase and gainconditions by a factor which is shown to have a simple geometrical representation. From this representation it is easily seen how the laser frequency spectrum and the threshold gain depend on external parameters such as distance to the reflection point and the amount of optical feedback.Furthermore, by inserting a variable attenuator in the external cavity and measuring the threshold current versus transmittance we have simultaneously determined the photon lifetime and the absolute amount of optical feedback. For the laser considered we found the photon life-