Observation of photon bunching near the threshold of laser diode

Ren Fang Chang, Robert W. Detenbeck, Victor Korenman +2 more

Yujiang Qu, Surendra Singh

Second-harmonic generation (SHG) has been predicted to be very sensitive to photon bunching. Because of its two-photon nature SHG would be more efficient with bunched than with random or antibunched photon sequences of the same mean intensity. We use this phenomenon to demonstrate the bunching of photons in time. The fundamental beam, derived from a laser operating near threshold, was focused into a 90° temperature phase matched nonlinear crystal. The operating point of the laser was varied in the neighborhood of threshold, and a feedback loop stabilized its intensity at each operating point. It is well known that the character of laser light changes in passing the threshold of laser action. Underlying photon sequences are bunched below threshold and random above threshold.

Andreas Jechow, Michael Seefeldt, Henning Kurzke +2 more

Two-photon excited fluorescence (TPEF) has become a standard technique in modern microscopy but it is still affected by photo-damage of the probe owed to high excitation intensities. This work reports on utilizing the photon bunching effect in thermal light to enhance the efficiency of TPEF under continuous wave excitation. A super-luminescence diode (SLD) was used as thermal light source and compared it to coherent excitation from a DFB diode laser emitting at the same wavelength. The degree of second order coherence g(2)of both sources was measured. The SLD showed photon bunching with g(2)= 1.90±0.2 as expected for thermal light, while the DFB diode laser emitted coherent light exhibiting no photon bunching at g(2)= 1.

Anders Smith, John A. Armstrong

Peng Kian Tan, Christian Kurtsiefer

We demonstrate an optical ranging technique using stationary light implemented on a semiconductor laser diode operating below threshold, with the required time-of-flight information extracted from thermal photon bunching. In contrast, conventional ranging techniques require a light source to be timing modulated in intensity, phase, or frequency, with which to correlate the reference and probe-to-target beams. This reference-probe correlation provides for time-of-flight information from which the target distance can then be measured. Presently, quantum ranging schemes derive timing correlation information from spontaneous parametric down-conversion sources which need not be timing modulated [1] , [2] . However, such light sources are complex and expensive to construct.

Anders Smith, J. Armstrong