We present a direct comparison between resonant terahertz (THz) and nonresonant impulsive stimulated Raman scattering (ISRS) excitation of phonon-polaritons in ferroelectric lithium niobate. THz excitation offers advantages of selectively driving only the forward propagating phonon-polariton mode to exceedingly high amplitudes, without complications due to nonlinear processes at the high 800 nm pump fluences used in Raman excitation. At peak-to-peak THz electric field strengths exceeding 1 MV/cm, the ferroelectric lattice is driven into the anharmonic regime, allowing experimental determination of the shape of the potential energy surface.Ultrafast control over a crystalline lattice is of interest in developing a basic understanding of how light can influence material properties, as well as potential practical applications such as the development of ultrafast switches and a variety of optoelectronic applications [1][2][3][4]. Strong THz radiation, with frequencies resonant to the modes of interest, has been promoted as a preferred means of lattice control [1] over two common routes: displacive excitation [5,6] and nonresonant Raman excitation of vibrations [7][8][9]. In typical displacive-type excitation, energy is deposited into the material's electronic subsystem, transiently distorting the lattice. Such excitation may coherently drive many modes simultaneously, but potentially leaves large amounts of (unwanted) incoherent thermal energy. Nonresonant ultrafast Raman excitation, termed impulsive stimulated Raman scattering (ISRS) [7-9], can coherently excite lattice modes without the excess thermal energy, but it is an inefficient process and thus extremely high-fluence laser pulses are required to a

A 29‐year‐old male presented with a two‐week history of a tender lesion on his right thigh. The lesion was a 1.5 cm erythematous nodule with overlying hemorrhagic crust. Histopathologic examination of a biopsy specimen revealed a highly cellular neoplasm with irregular vesicular nuclei, prominent nucleoli, and scattered mitotic figures. The cells within the lesion were rounded, ovoid and spindle shaped cells with perivascular growth. The architecture and staining pattern of the lesion were most consistent with a diagnosis of malignant myopericytoma, an exceedingly rare malignancy.

J Cutan Pathol. 2018;45:97-98.wileyonlinelibrary.com/journal/cup 97 Fluorescent in situ hybridization (FISH) can be a helpful adjuvant test in categorizing atypical melanocytic proliferations into benign or malignant based on aberrations (gains or losses) in loci on chromosomes 6, 9 and 11. 5,6 The reported sensitivity and specificity is 86% and 97%, respectively. Notably, FISH studies are negative in up to 10% to 20% of melanomas, which makes exclusion of melanoma in this case not feasible by FISH alone. 5 FISH analysis of 5-FU induced melanocytic atypia has not been previously described.5-FU alters DNA synthesis and repair, but its effects on melanocytes has not been evaluated. The significance of a negative FISH in this setting is unclear.This case illustrates the difficulty when lesions are biopsied in a treatment field during or immediately following topical 5-FU therapy. The histopathologic features were consistent with melanoma; however, melanoma was not considered clinically until therapy was near completion. Prominent pagetoid scatter and subepidermal clefting has not been described in 5-FU treated melanocytic lesions and these findings are found in melanoma. This raises the question as to whether this lesion was a melanoma not clinically apparent prior to therapy, was a benign nevus or lentigo that transformed during therapy, or a therapy-induced pseudomelanoma as the FISH studies showed no aberrations. We originally considered the lesion to be pseudo-melanoma. This case was sent for expert consultation and interpreted as malignant melanoma to a depth of 0.2 mm, as a single dermal nest was found in deeper levels. The lesion was ultimately treated as a superficially invasive melanoma because of the architectural features and the patient had a 1-cm wide local excision to ensure complete removal.The true nature of the lesion remains unclear, as both melanoma and a melanocytic lesion with 5-FU-induced atypia remain in the differential diagnosis.