Laser produced plasmas (LPPs) offer a compact and affordable route to soft X-ray (SXR) illumination of biological samples for microscopy in the water window (WW), the spectral region between 2.34 and 4.38 nm. The radiance of an LPP source scales with laser repetition rate and individual plasma radiance. The latter is optimised by maximizing conversion efficiency from laser light to SXR radiation while also reducing the emission area of the plasma. This is the first detailed study reporting plasma emission area and its contribution to radiance improvement for a range of solid metal target materials. Based on a 6 ns 1064 nm laser, radiance across the water window region is optimised by illuminating a molybdenum target with 38 mJ to 77 mJ of laser energy, creating a plasma emission area of $65\mathrm{\mu }{\mathrm{m}}^2$ to $115\mathrm{\mu }{\mathrm{m}}^2$. An estimate of the absolute radiance is provided for comparison with bending magnets at synchrotrons.

激光产生的等离子体（LPP）为生物样品的软X射线（SXR）照明提供了一种紧凑且价格合理的途径，用于在水窗（WW）（光谱范围介于2.34和4.38 nm之间）进行显微镜检查。LPP源的辐射度与激光重复率和各个等离子体的辐射度成比例。通过最大化从激光到SXR辐射的转换效率，同时减小等离子体的发射面积，可以优化后者。这是第一个详细的研究，报告了等离子体发射区域及其对一系列固体金属靶材对辐射改善的贡献。基于6 ns 1064 nm激光，通过用38 mJ到77 mJ的激光能量照射钼靶，优化了整个水窗区域的辐射，从而产生了等离子发射区。$\mathrm{65岁}\mathrm{\mu }{\mathrm{米}}^2$ 至 $115\mathrm{\mu }{\mathrm{米}}^2$。提供了绝对辐射的估计值，以便与同步加速器上的弯曲磁体进行比较。