Conversion of Electrical Input Delivered to the Pump Source to Useful Pump Radiation

We define as useful radiation the emission from the pump source that falls into the absorption bands of the laser medium. The pump source efficiency η_P is therefore the fraction of electrical input power that is emitted as optical radiation within the absorption region of the gain medium. The output of a laser diode or a diode array represents all useful pump radiation, provided the spectral output is matched to the absorption band of the gain medium. Typical values of ηp for commercially available cw and quasi-cw diode arrays are 0.3 to 0.5.
For flashlamp or cw arc lamp-pumped systems, the pump source efficiency may be defined as

........(1)

where P_λ is the spectral output power of the lamp within the absorption bands of the gain material, Pin is the electrical power input, and P'_λ is the radiative power per unit wavelength emitted by the lamp, and the integral is taken over the wavelength range λ₁ to λ₂, which is useful for pumping the upper laser level. The output characteristics of arc lamps and their dependency on operating parameters. The measurement of η_p for broadband sources is somewhat involved and requires either a calorimetric measurement of the power absorbed in a sample of the laser material or integration over the source emission spectrum and the absorption spectrum of the gain material. Typical values are η_p = 0.04–0.08. These numbers are typical for a 5 to 10mm thick laser material. The magnitude of η_P is dependent on the thickness of the active material because as the thickness increases, radiation at the wings of the absorption band will start to contribute more to the pumping action.