Two-photon resonant parametric four-wave mixing and a newly developed variant called seeded parametric four-wave mixing are used to detect trace quantities of sodium in a flame. Both techniques are simple, requiring only a single laser to generate a signal beam at a different wavelength which propagates collinearly with the pump beam, allowing efficient signal recovery. A comparison of the two techniques reveals that seeded parametric four-wave mixing is more than two orders of magnitude more sensitive than parametric four-wave mixing, with an estimated detection sensitivity of 5 x 10(9) atoms/cm(3). Seeded parametric four-wave mixing is achieved by cascading two parametric four-wave mixing media such that one of the parametric fields generated in the first high-density medium is then used to seed the same four-wave mixing process in a second medium in order to increase the four-wave mixing gain. The behavior of this seeded parametric four-wave mixing is described using semiclassical perturbation theory. A simplified small-signal theory is found to model most of the data satisfactorily. However, an anomalous saturationlike behavior is observed in the large signal regime. The full perturbation treatment, which includes the competition between two different four-wave mixing processes coupled via the signal field, accounts for this apparently anomalous behavior.
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机译:两光子共振参数四波混合和一种新开发的称为种子参数四波混合的变体用于检测火焰中的痕量钠。两种技术都很简单,仅需单个激光器即可产生不同波长的信号光束,该信号光束与泵浦光束共线传播,从而实现有效的信号恢复。两种技术的比较显示,种子参量四波混合比参量四波混合灵敏度高两个数量级,估计检测灵敏度为5 x 10(9)atoms / cm(3)。通过级联两种参数四波混合介质来实现播种参数四波混合,这样,在第一高密度介质中生成的一个参数场便可以用于在第二介质中按顺序播种相同的四波混合过程。增加四波混频增益。使用半经典摄动理论描述了这种种子参量四波混频的行为。发现简化的小信号理论可以令人满意地对大多数数据进行建模。但是,在大信号方案中观察到异常饱和类似的行为。完全扰动处理(包括通过信号场耦合的两个不同的四波混频过程之间的竞争)解释了这种明显的异常行为。
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