🔬 DIY SPDC Entangled-Photon Lab Shopping List

This list covers the core components—lasers, crystals, optics, detectors—along with reputable vendors (academic/industrial, no affiliate marketing). Everything on this list is buildable by a well-equipped hobbyist with good alignment skills.

1. Pump Laser (≈405 nm diode)

• A 405 nm diode laser with adjustable current & temperature. Tech grade (a few mW) is enough.
  • Available from hobby/laser-specialist stores (e.g., eBay or AliExpress “405 nm laser diode module”). Choose TEC-stabilized for beampoint stability.

2. SPDC Crystal – β‑BBO

• Type-I or Type-II β‑BaB₂O₄ (BBO) crystal, AR-coated for 405→810 nm.
  • Newlight Photonics (USA): BBO crystals cut and AR-coated, mounted 5×5 mm, ideal for lab setups :contentReference[oaicite:1]{index=1}.
  • Thorlabs (NJ, USA): Offers 1 in mounted β‑BBO for SPDC at 405 nm, Type-I/II, with rotation mounts and detailed specs :contentReference[oaicite:2]{index=2}.
  • EKSMA Optics (Lithuania/EU): Offers a variety of BBO crystals (mounted/unmounted, custom coatings) starting ≈$400 :contentReference[oaicite:3]{index=3}.
• Optional: Paired-crystal setup (two Type-I rotated 90°) for polarization entanglement :contentReference[oaicite:4]{index=4}.

3. Optics & Mounts

• AR-coated long-pass filter (OD ≥ 7) to block pump and pass 810 nm.
  • Thorlabs catalog includes suitable filters with datasheets.
• λ/2 waveplate, polarizing beam splitters (PBS), mirrors, irises, lenses—available via Thorlabs or local optics labs.
• Precision kinematic mounts, rotation stages (e.g., Thorlabs RSP1), and posts for alignment :contentReference[oaicite:5]{index=5}.

4. Single‑Photon Detectors (SPAD or single-photon module)

• Single‑photon avalanche diodes (SPADs) or photon-counting modules:
  • Hamamatsu: scientific‑grade SPAD modules, <7 cps dark count, built-in temperature control :contentReference[oaicite:6]{index=6}.
  • PicoQuant (Magellan Photonics): PDM series with timing resolution <50 ps, active areas 20–100 µm, fiber coupler options :contentReference[oaicite:7]{index=7}.
  • Wooriro InGaAs/InP SPAD for 1100–1600 nm (if you want NIR entangled photons) :contentReference[oaicite:8]{index=8}.
  • Axiom Optics “SPAD23” array for timing-critical experiments or camera style setups :contentReference[oaicite:9]{index=9}.

5. Timing Electronics

• Time-correlated single-photon counting module (e.g., PicoHarp, HydraHarp).
• PicoQuant or similar pulsed laser controllers and detection integration modules.

6. Misc & Enclosure

• Optical breadboard or rail system with posts.
• Black hose or tubes for dark-path alignment.
• Safety goggles rated for 405 nm UV/blue.

💡 Tips

• Use dark enclosure, baffles, and pinholes to minimize background.
• Walk-off in BBO: expect a few % conversion—longer crystals help (Type-I easier to align) :contentReference[oaicite:10]{index=10}.
• Paired-crystal entanglement increases brightness and Bell–test visibility :contentReference[oaicite:11]{index=11}.

Putting It All Together

1. Mount laser → focus onto AR filter into BBO → align entangled cones.
2. Place polarizers/PBS in each arm, coupling into SPADs or fibers.
3. Use long-pass filter to block pump before detectors.
4. Record coincidences and measure polarization correlations.

This builds a classic SPDC entanglement setup similar to Veritasium’s—but with scientific-grade parts you can actually source. Let me know if you'd like diagrams or exact part numbers!