Photoacoustic imaging has attracted increasing research interest in recent years, due to its unique merit of combining light and sound. Enabling deep tissue imaging with high ultrasound spatial resolution and optical absorption contrast, photoacoustic imaging has been applied in various application scenarios including anatomical, functional and molecular imaging. However, the bulky and expensive laser source is one of the key bottlenecks that needs to be addressed for further compact system development. A photoacoustic imaging system based on a low-cost laser diode (LD) is one of the promising solutions. In this paper, we report a custom-made fingertip laser diode system enabling both pulsed and continuous modulation modes with shortest pulse-width of 40 ns, largest driving current of 13 A, and highest modulation frequency of 3 MHz, which is suitable for both time and frequency domain photoacoustic imaging. To the best of our knowledge, this may be the most compact laser source reported for photoacoustic imaging enabling both two modulation modes. Owing to its super-compact size, the proposed LD system could pave the pathway to a low-cost photoacoustic sensing and imaging device, even wearable photoacoustic biomedical sensors.