720 nm diode lasers enhancing cancer diagnostics
Fig. 1: Micro-module with high-power 720 nm emitting diode laser for quantum-interference applications.
Fig. 2: Power-current characteristics of high-power diode laser sources emitting at 720 nm.
Fig. 3: Emission spectra of high-power diode laser sources emitting at 720 nm.
With ongoing research in the field of quantum technologies, new applications arise, and existing schemes can be significantly improved. For example, quantum interference can be utilized in a concept referred to as “sensing with undetected photons” to enable hyperspectral imaging of human tissue in the mid-infrared spectral range. Compared to conventional imaging techniques, this approach reduces measurement time from hours to minutes. However, it also imposes high demands on high-power laser sources emitting at 720 nm. Additionally, diode lasers at emission wavelengths around 720 nm are extremely challenging to manufacture due to internal strain in the active zone.
At FBH, we have developed diode lasers emitting at 720 nm to fulfill the demands in quantum technologies. Beyond enabling these applications, the compact size and high efficiency of diode lasers allow for a high degree of miniaturization. Fig. 1 shows an example of a miniaturized diode laser module with watt-level output power at 720 nm. To address varying requirements, different diode laser types have been fabricated. All devices make use of FBH’s in-house deeply etched grating technology to realize distributed Bragg reflector (DBR) gratings for narrow-band emission at 720 nm.
For high-power operation, two devices are of special interest: the hybrid master oscillator power amplifier (MOPA) system and the distributed Bragg reflector tapered laser (DBR-TPL).
In a hybrid MOPA, a DBR ridge waveguide laser (DBR-RWL) serves as a master oscillator, providing several milliwatt optical power and a narrow spectral width of the emission. Coupled into a tapered amplifier (TPA), the optical output power is raised to the watt level. Fig. 2 shows the power-current characteristic of the MOPA, where the pump current through the TPA is varied. At maximum, more than 4.4 W of optical output power is reached. After the amplification a narrow spectral width below 10 pm is maintained, as illustrated in Fig. 3.
The DBR-TPL is a monolithic alternative to the hybrid MOPA. While the setup is simpler, its maximum output performance is slightly lower. This device achieves more than 1.9 W of optical output power, as shown in Fig. 2. Its emission spectrum at maximum output power, shown in Fig. 3, indicates a spectral width below 10 pm.
The diode laser sources presented here are unique worldwide, achieving the highest power for narrow-band diode lasers at 720 nm to date. Their development represents a significant advancement in quantum-based sensing applications for cancer diagnostics.
This work is sponsored by the German Federal Ministry of Education and Research (BMBF) within the projects “Sim-QPla” (FKZ 13N15943) and “QEED” (FKZ 13N16381).
Publications
N. Werner et al. „High-Power Semiconductor Laser Systems at 720 nm: Tailored Laser Light Delivery for Quantum Technologies”, High-Power Diode Laser Technology XXIII, SPIE (2025).
F. Mauerhoff et al. “GaAs based edge emitters at 626 nm, 725 nm and 1180 nm”, IEEE JSTQE, vol. 31 (2025).
P. Hildenstein et al. “Compact Quantum Light Source for Mid-Infrared Spectroscopy: Design, Simulation and Experimental Validation”, Sensing with quantum light (2024).