ABSTRACT
We propose a device to compensate for group-velocity mismatch (GVM) effects that limit the efficiency-bandwidth product in nonlinear frequency-mixing devices. Integrated wavelength-dependent delay lines are introduced periodically in a waveguide containing a series of quasi-phase-matching (QPM) gratings. Appropriate choice of the time delays can compensate for GVM. We have demonstrated a two-stage device in a periodically poled lithium niobate waveguide. Two approximately 150-fs-long pulses generated 6 ps apart by second-harmonic generation in two QPM gratings were resynchronized by a fixed delay line, and their relative phase was fine controlled by temperature tuning. This technique, which can be iterated to more than two segments, permits optical frequency mixers with a higher efficiency-bandwidth product than would be possible in a single grating short enough to avoid GVM effects.
ABSTRACT
We demonstrate continuously tunable compensation of linear chirp on a first-harmonic pump pulse to produce a near-transform-limited second-harmonic output pulse through the use of a chirped, fanned, periodically poled lithium niobate quasi-phase-matching grating. Compensation of positive and negative chirps is possible through reversal of device orientation. The device is simple and monolithic and can be applied to compensation of a higher-order phase with minor modification.
ABSTRACT
The frequency of sister chromatid exchanges (SCEs) in the centromere of chromosomes involved in a whole-arm translocation t(1:19) was evaluated in altogether 911 metaphases of translocation carriers (n = 5) and of normal controls (n = 6). Comparison of the two groups reveals no significant differences in the SCE rate (x2 = 3.06, nf = 1). The question as to whether the possible increase of the SCE rate at the translocation point could be detected by light microscopy is discussed. Parameters included in the discussion are the ratio of the SCE frequency at the translocation point to the SCE frequency at any of the possible breakage points in the centromeric region and the number of possible breakage points in the centromeric region.
Subject(s)
Chromosome Aberrations/diagnosis , Crossing Over, Genetic , Lymphocytes/cytology , Sister Chromatid Exchange , Chromosome Disorders , Fluorescence , Humans , Metaphase , Translocation, GeneticABSTRACT
Seven carriers of a balanced reciprocal whole-arm translocation of chromosomes 1 and 19 were found in 19 members investigated in three generations of one family. The apparent lack of a carrier of an unbalanced form of the translocation and of a history of miscarriages are discussed.
