We demonstrate quantum interference control of injected photocurrents in a semiconductor using the phase stabilized pulse train from a mode-locked Ti:sapphire laser. Measurement of the comb offset frequency via this technique results in a signal-to-noise ratio of 40 dB (10 Hz resolution bandwidth), enabling solid-state detection of carrier-envelope phase shifts of a Ti:sapphire oscillator.

We demonstrate precise linearization of ultrabroadband laser frequency chirps via a fiber-based self-heterodyne technique to enable extremely high-resolution, frequency-modulated cw laser-radar (LADAR) and a wide range of other metrology applications. Our frequency chirps cover bandwidths up to nearly 5 THz with frequency errors as low as 170 kHz, relative to linearity. We show that this performance enables 31-mum transform-limited LADAR range resolution (FWHM) and 86 nm range precisions over a 1.5 m range baseline. Much longer range baselines are possible but are limited by atmospheric turbulence and fiber dispersion.

As the bandwidth and linearity of frequency modulated continuous wave chirp ladar increase, the resulting range resolution, precisions, and accuracy are improved correspondingly. An analysis of a very broadband (several THz) and linear (<1 ppm) chirped ladar system based on active chirp linearization is presented. Residual chirp nonlinearity and material dispersion are analyzed as to their effect on the dynamic range, precision, and accuracy of the system. Measurement precision and accuracy approaching the part per billion level is predicted.

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We demonstrate carrier-envelope phase stabilization of a mode-locked Ti:sapphire laser by use of quantum interference control of injected photocurrents in a semiconductor. No harmonic generation is required for this stabilization technique. Instead, interference between coexisting single- and two-photon absorption pathways in the semiconductor provides a phase comparison between different spectral components. The phase comparison, and the detection of the photocurrent that it produces, both occur within a single low-temperature-grown gallium arsenide sample. The carrier-envelope offset beat note fidelity is 30 dB in a 10-kHz resolution bandwidth. The out-of-loop phase-noise level is essentially identical to the best previous measurements with the standard self-referencing technique.

Photon-number fluctuations 1.3 dB below the semiclassical shot-noise limit are observed in the output of a semiconductor microcavity laser. Although the laser oscillates in a single longitudinal mode, photon-number squeezed light is realized through nonclassical correlations between two orthogonally polarized, transverse laser modes. ͓S1050-2947͑97͒50705-0͔PACS number͑s͒: 42.50. Dv, 42.55.Sa When the direct generation photon-number squeezed light from an optical source was first demonstrated ͓1͔, this macroscopic quantum effect was scarcely measurable due to the debilitating effect of high optical losses. Shortly thereafter, the laser emerged as a natural solution to this problem.Yamamoto and co-workers demonstrated that the laser, previously thought to be limited to coherent-state output, can naturally emit photon-number squeezed light ͓2͔. In particular, the semiconductor laser features the essential elements necessary to realize photon-number squeezed output, including high-efficiency operation at high pump rates and pumpnoise suppression through the drive current. Laser pump noise, which limits the low-frequency intensity noise on the output of a laser at high pump rates, can be suppressed below shot noise ͓2,3͔, resulting in photon-number squeezed output. Recently, the collimated output of cryogenically cooled semiconductor quantum-well lasers demonstrated large ͑4.5 dB͒ squeezing near levels expected from the device efficiency ͓4͔, and previous measurements suggest that the squeezing may reach limits associated with a laser's optical efficiency ͓5͔. Indeed, during the past decade considerable progress has been made in understanding the quantum-noise processes of conventional semiconductor lasers ͓2,4-6͔ and photon-number squeezed light has reached the predicted device efficiency limits. Despite this progress in the generation of photon-number squeezed light from conventional semiconductor lasers, the photon-number fluctuations previously observed from electrically pumped microcavity semiconductor lasers have been limited to an order of magnitude above shot noise ͓7͔.Nevertheless, the microcavity laser has been proposed as an ideal source for photon-number squeezed light, with several important benefits over conventional semiconductor lasers. Microcavity devices are characterized by a cavity length matched to the wavelength of light. This extreme reduction in mode volume, potentially enhanced by cavity quantum electrodynamic effects ͓8͔, results in a significant enhancement of the fraction of spontaneous emission into the lasing mode. Ultimately suppression of all emission into nonlasing modes can result in squeezed output for all laser pump rates ͓9͔ ͑i.e., high efficiency without the need for stimulated emission͒. While this effect is not achieved in present devices, the small volume contributes to submilliampere threshold currents. The benefit of a low threshold is that the high pump rates necessary to generate squeezed output may be achieved at room temperature without damage to the laser. Typical se...

The optical frequency sweep of an actively linearized, ultrabroadband, chirped laser source is characterized through optical heterodyne detection against a fiber-laser frequency comb. Frequency sweeps were measured over approximately 5 THz bandwidths from 1530 nm to 1570 nm. The dominant deviation from linearity resulted from the nonzero dispersion of the fiber delay used as a reference for the sweep linearization. Removing the low-order dispersion effects, the residual sweep nonlinearity was less than 60 kHz rms, corresponding to a constant chirp with less than 15 ppb deviation across the 5 THz sweep.

What is to the authors' knowledge the first experimental demonstration of a nonresonant cw Raman laser pumped by a tunable external-cavity diode laser (ECDL) is presented. The ECDL is phase-frequency locked to a high-finesse Raman laser cavity containing diatomic hydrogen (H(2)) by the Pound-Drever-Hall locking technique. The Stokes lasing threshold occurs at a pump power of 400 +/- 30 muW, and a maximum photon conversion efficiency of 12.0 +/- 1.3% is achieved at 1.6 mW of pump power. A 40-nm tuning range of the cw Stokes emission, 1174-1214 nm, is obtained by tuning of the wavelength of the ECDL pump source.