Diode laser direct modulation heterodyne interferometer

Abstract

A new type of heterodyne interferometer was made through direct modulation of a diode laser wavelength. A measurement accuracy of better than lambda/50 and repeatability of lambda/100 were obtained. This interferometer shows promise for use in testing wavefront aberrations, especially in optical disk systems.

Static wavelength scanning using tunable external cavity laser diode

“…4, we observed a continuous interference signal S͑t͒ that exhibits a partially sinusoidal waveform in the linear region of the triangular wave. 14 The modulation frequency in Fig. 4 was 1 kHz, and we were able to observe a stable interference signal up to this frequency.…”

Out-of-plane vibration analysis with a transmission holographic-optical-element-based electronic speckle pattern interferometer

“…In this work a 532 nm Verdi laser was used to record the holograms and a 763nm near infrared distributed feedback (DFB) diode laser was used for reconstruction. Phase shifting can be implemented by modulating the wavelength of the near infrared diode laser in an unbalanced interferometer 8,9 . There are no commercial holographic recording materials available which are sensitive at 763nm to record a hologram.…”

Moving ahead with phase

“…As stated earlier, one of the ways by which the phase shifts can be realized is by varying the injection current and/or the temperature of the active regions in the laser diode. By doing so, the laser diode frequency can be changed [24][25][26][27][28]. An increase of current, however, gives rise to an increase of the power of the laser diode, which violates the assumption of constant intensity in the phase extraction algorithm [25].…”

“…An increase of current, however, gives rise to an increase of the power of the laser diode, which violates the assumption of constant intensity in the phase extraction algorithm [25]. Tatsuno and Tsunoda [26], have shown that the use of a photodiode can minimize this problem; while Ishii et al [24] have proposed a numerical approach to minimize the variation in intensity. Another approach that has been suggested [27] uses an amplitude stabilizer with the objective to stabilize the laser diode source.…”