shg

SHG is an acronym that can refer to several terms in different fields. The two most common meanings are Second Harmonic Generation in optics and Self-Help Group in social development. The term may also appear in other contexts, but these are the most widely used in scientific and development literature.

Second Harmonic Generation refers to a nonlinear optical process in which two photons of the same frequency interact with a non-centrosymmetric material to produce a new photon with twice the energy, i.e., at twice the frequency (half the wavelength) of the original light. The efficiency of SHG depends on the material’s second-order nonlinear susceptibility, phase matching, the intensity of the input beam, and the interaction length within the crystal. Common SHG media include crystals such as lithium niobate, beta barium borate, and potassium titanyl phosphate. Practical applications include frequency doubling of laser light, enabling visible output from infrared sources, and use in imaging and spectroscopic techniques such as SHG microscopy and nonlinear optical spectroscopy. SHG is a coherent process whose signal scales with the square of the input field and requires careful control of phase relationships.

Self-Help Group refers to small, voluntary associations of local people—often women—formed to save money and provide mutual credit. SHGs typically consist of 10–20 members who meet regularly to contribute savings, create a pooled fund, and extend small loans to members. They can be linked to formal financial institutions to access larger credit and to government or NGO programs that support microfinance and poverty reduction. Benefits include increased financial inclusion, social empowerment, and collective bargaining, while challenges can include governance, repayment risk, and the need for capacity building. In some countries, SHGs are a key element of development strategies and bank-linkage programs.