Abstract
We report the absorption spectroscopy of 4He1H+ at 4.3 μm by velocity modulation. The light source is CW mid-infrared difference frequency generation (DFG) generated in periodically poled lithium niobate (PPLN) nonlinear crystal by mixing a Nd-YAG laser and a Ti-Sapphire laser. The Nd-YAG laser is stabilized onto 127I2. The Ti-Sapphire laser is scanned near 852 nm. The discharge cell is full of HeH+ generated in 99 % helium and 1 % hydride, total pressure is about 2 torr . The experimental setup of velocity modulation consists of function generator, power amplifier, and high frequency transformer. The two electrodes of discharge cell are connected to AC sine wave source about 15 kHz, and the voltage is about 1 kV. We find the background arising from emission of the discharge too large to search the signal of HeH+ spectroscopy. We still try to find out the solutions to diminish the background of the emission.