Concentration, Dharana, gives the ability to focus awareness on any given object, gross or subtle.
To hold the mind still is known as concentration. The pure, exclusive throught "I AM He', Pure Consciousness, is called contemplation. When the very thought of contemplation subsides, this is known as absorption (samadhi).
Upanisads
Sakti Kriya utilizes the trinity of prana (breath), mantra (sound), and pasyanti (light) to develop concentration power. It is also known as kundalini-in-action. This trinity is a powerful tool to focus and calm the mind. It serves as a bridge to cross from the outer world into the inner world.
Nada Prasyanti Variation 1 (Sound Light)

The light is limitless and the cosmic sound is continuous. Feel the expansiveness of consciousness as the energy permeates the body, mind, and spirit.

OM is the mantra for the Universal Energy.
AH is the mantra for sahasrara cakra (crown energy center) which represents Universal Consciousness.