Robert W. Schirmer

HIGH-REFLECTIVITY, WIDE-BANDWIDTH OPTICAL PHASE CONJUGATION VIA FOUR-WAVE MIXING IN POTASSIUM VAPOR

We report on a high‐reflectivity (up to 670%) wide‐bandwidth (up to 230 MHz) phase‐conjugate mirror formed using backward‐four‐wave mixing with continuous‐wave pump beams in a 2‐mm potassium vapor cell. The reflectivities and bandwidths are significantly larger than have been measured previously, and the bandwidth is ten times greater than is predicted theoretically. The reflectivity‐bandwidth product is more than an order of magnitude improvement over those previously achieved with other continuous‐wave phase‐conjugate systems.

Nonlinear mirror based on two-photon absorption

ing solar UV band 300-320 nm. The recent development of red diode lasers has made frequency doubling to this UV band possible. Despite the low power of the lasers, secondharmonic generation using a nonlinear crystal in a resonant buildup cavity offers an efficient way to generate ultraviolet radiation. By this method, 18 pW1 and 35 pW2 at 369 nm, and 260 pW at 344 nm3 have recently been generated. In this paper we report a compact laser system to generate continuous wave radiation around 3 I 7 nm. Presently, there are 15 mW AlGaInP diode lasers available around 635 nm. With these lasers some difficulties have to be solved before they can be used with a resonant buildup cavity; the spectrum is generally multimode with broad lines (100 MHz) and the output beam profile is elliptical. To overcome these problems without loosing optical power we have used a diode laser (BlueSky Research PS010) that is equipped with a virtual point source microlens.4 The microlens produces a circularized, diffraction-limited output beam. In addition, this closely mounted (30 pm) microlens provides weak optical feedback and thus results in a single-longitudinal-mode output with narrowed linewidth. We measured the instantaneous linewidth of the laser to be 2 MHz. The setup of the frequency doubling system is shown in Fig. 1. The whole mechanical structure measures only 5 X 7 X 30 cm3. Rubidium dihydrogen phosphate (RDP) is used as the nonlinear crystal because of its noncritical phase-matching around 630 nm.5 The buildup cavity is formed by four mirrors in a bow-tie ring configuration. Optical feedback from the cavity is used to lock the laser frequency to a cavity resonance. The error signal that controls the phase of the feedback light is generated by the polarization method.6 The transmission (1.5%) of the input mirror is matched to the cavity losses and a power buildup factor of about 55 is achieved. When 10 mW of the fundamental power was coupled into the cavity (35% reflected) the generated UV radiation was 31 pW. The result agrees well with the theoretical value. By changing the temperatures of the diode laser and the RDP crystal the output wavelength can be adjusted between 315 and 318 nm. ica, Washington, DC, 1994), postdeadline paper CPD 18. S. W. Connely and J. J. Snyder, Proc. SPIE 2383,252 (1995). R. S. Adhav and R. W. Wallace, IEEE J. Quantum Electron. QE-9,855 (1973). T. W. Hansch and B. Couillaud, Opt. Commun. 35,441 (1980). 4.

Quantum Noise in Optical Phase Conjugation Performed in an Atomic Vapor

Many researchers have studied the noise properties of optical amplifiers and have shown that all nonlinear optical amplifiers introduce noise into the amplified beam.1 In our research, we have conducted a theoretical and experimental investigation of the quantum noise generated by a phase-conjugate mirror (PCM) obtained using four-wave mixing in potassium vapor. An ideal PCM will generate light that exhibits excess quantum noise that is inherent to the phase conjugation process.2 Additional noise can be introduced as a result of fluctuations (e.g., collisions) in the nonlinear medium, as has been predicted for the nonlinear process of two-beam coupling in an atomic vapor.3 These sources of noise determine the fundamental limit on the smallest signal that can be phase-conjugated.

Spectral Modification of Ultrashort Pulses Propagating through an Atomic Vapor

Extensive research has been performed on the temporal behavior of resonant short pulses propagating through an atomic vapor.1 In our studies, we have investigated experimentally and theoretically the modification of the spectrum of pulses propagating through an atomic vapor under conditions in which the pulse duration is much shorter than any of the relaxation times of the atomic system. We observe novel features in the spectrum of the transmitted pulse under conditions in which the area of the incident pulse is of the order of unity or greater.